Science Focus 1

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Kerry Whalley Geoff Phillips Greg Rickard Stewart Monckton Peter Roberson

Sydney, Melbourne, Brisbane, Perth and associated companies around the world

Pearson Education Australia A division of Pearson Australia Group Pty Ltd Level 9, 5 Queens Road Melbourne 3004 www.pearsoned.com.au/schools Offices in Sydney, Brisbane and Perth, and associated companies throughout the world. Copyright © Pearson Education Australia (a division of Pearson Australia Group Pty Ltd) 2004 First published 2004 Reprinted 2005 All rights reserved. Except under the conditions described in the Copyright Act 1968 of Australia and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright owner. Designed by Polar Design Edited by Kay Waters Prepress work by The Type Factory Set in Melior 10 pt Printed in China National Library of Australia Cataloguing–in–Publication data: Whalley, Kerry. Science focus 1. For secondary school students. ISBN 0 12 360444 3. 1. Science - Textbooks. I. Roberson, Peter. II. Rickard, Greg. III. Title. IV. Title : Science focus one. 500

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Solids, liquids and gases

UNIT

2

2.1 The particle model 2.2 Changes of state

UNIT

3 6 9 12 15 18 24 27 32

34

Science focus: Observation and discovery 2.3 Expansion 2.4 Density Chapter review

Mixtures and their separation

61

3.1 3.2 3.3 3.4

Types of mixtures Separating insoluble substances Separating soluble substances Water supply and sewage Chapter review

Cells

4

4.1 4.2 4.3 4.4

The microscope Plant and animal cells Specialised cells Groups of cells Science focus: Stem cells Chapter review

UNIT

5.1 5.2 5.3 5.4

Energy Heat Light Sound Chapter review

Classification

6

6.1 6.2 6.3 6.4 6.5

Being alive From kingdom to species Animal classification Plants and other kingdoms More on keys Chapter review

Forces

7 35 41 46 48 54 60

3

UNIT

2

UNIT

Safety—before we start What is science? Observing Equipment Reporting Measurement Working scientifically Using a Bunsen burner Chapter review

62 69 74 79 85

UNIT

UNIT

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

Heat, light and sound

5

moving Science focus: Flying high 7.5 Forces in water 7.6 Magnetic forces Chapter review

Earth and space

8

86 87 94 99 103 108 111

7.1 Forces: what are they? 7.2 Balanced and unbalanced forces 7.3 Friction: slowing down and getting 7.4 Gravity

UNIT

Being a scientist

1

iv v viii 1

8.1 The solar system Science focus: Early astronomy 8.2 The Sun 8.3 Earth’s movement in space 8.4 The Moon Chapter review

Our planet Earth

9

UNIT

Acknowledgements Introduction Verbs Curriculum grids

9.1 9.2 9.3 9.4 9.5

Our Earth Rocks and minerals Types of rocks Weathering and erosion The atmosphere Science focus: Global warming 9.6 Weather Chapter review

Index

112 113 118 129 137 145

147 148 155 161 171 176 181

182 183 188 191 196 201 204 208 213

215 216 228 231 235 239 245

246 247 251 256 264 269 276 279 285 287

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We thank the following for their contributions to our text book:

National Safety Council of Australia Ltd: figure. 1.1.3 a-f.

Anglo-Australian Observatory/David Malin Images: figure 8.0.1.ANTphoto.com: Kelvin Aitken, figure 6.1.9.

National Science Foundation: Josh Landis, figure. 5.2.3 b.

Arts Centre, Concert Hall: figure 5.4.11. Australia Picture Library: figures SF2.1, 3.2.4, 4.4.4, 5.1.2 a&i, 5.1.4b, 6.1.2, 6.1.8, 6.3.4, 6.3.13, 6.3.16, 6.3.17, 6.4.4, 6.4.5, 6.4.6, 6.5.5, 7.0.1, 7.3.4, 9.2.4, 9.3.3, 9.3.5, 9.3.7, 9.3.14, 9.4.4. Bureau of Meteorology: figures 9.4.1, 9.6.6 a-h. Calder Park Racing Promotions Pty. Ltd: figure 1.2.1a. Cambridge University Press: illustration from Edward Arnold, Science Scene 1, 1990, figure 1.4.3. CSIRO: Science Image Online: figures 1.2.1b, 9.5.6, SF9.1, SF9.2; CSIRO Minerals, figure 3.2.7. Daniela Ciminelli © Pearson Education Australia: figures 1.6.7, 5.3.3, 5.3.4, 6.5.11. Dorling Kindersley: figures 2.2.1, 2.2.3, 2.2.5, 4.1.2, 4.1.15; Spike Walker, figures 4.1.16, 5.1.2f, 5.2.10 a&b, 9.2.1, 9.2.2, 9.2.5, 9.2.6, 9.2.7, 9.3.4, 9.3.6, 9.3.8, 9.3.10. Getty Images: figures 6.1.5, 7.2.1. Great Barrier Reef Marine Park Authority: figure SF9.5. Jeramey Jannene © 2003: provided with courtesy, figure 6.2.1. João Estêvão © 2004: provided with courtesy, figure. 6.3.20. Karly Abery © Pearson Education Australia: figures 1.2.1d, 2.1.1, 2.1.3, 2.1.4, 3.1.3, 3.1.7, 3.2.1, 3.3.5, 4.2.2, 7.3.5. Lisa Piemonte © Pearson Education Australia: figure. 3.1.10. Melbourne Water: figure. 3.4.4. NASA: Kennedy Space Center, figures 1.2.1e, SF7.3, 8.4.1, 9.5.2; JSC, figure 5.3.2; GRIN/James McDivitt, figure. 7.4.1; JPL/Caltech, figures 8.1.6, 8.1.8, 8.1.10, 8.1.15, 8.1.17, 8.1.19, 8.1.21, 8.2.2, 8.4.2, SF8.7; JPL/Space Science Institute, figure. 8.1.13.

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Newspix: Gary Graham, figure. 9.3.9. NOAA: Sanctuary Collection /Scot Anderson fig. 6.3.7; Corps Collection /Commander John Bortniak, figure. 8.2.5. NSW Fire Brigades: provided with courtesy, figure 5.3.13. Photolibrary.com: figures SF2.3, 3.0.1, 3.1.9, 3.3.1, 3.3.6, 4.0.1, 4.1.1, 4.1.3, 4.1.5, 4.1.6, 4.1.8, 4.1.9, 4.1.11, 4.1.12, 4.2.1, 4.2.6, 4.2.8, 4.3.2, 4.3.3, 4.3.7, SF4.4, 5.0.1, 5.1.1, 5.1.3, 5.2.5, 5.2.6, 5.3.5, 6.1.4, 6.2.2, 6.3.2a, 6.3.8, 6.3.14, 6.3.21, 6.4.7, 6.4.8, 7.3.1, 7.5.3, 7.6.1, 8.1.2, 8.1.4, 8.1.11, 8.4.5, 8.4.7, SF8.1, SF8.2, SF8.4, SF8.5, SF8.6, 9.2.3, 9.2.8, 9.3.2, 9.6.7, 9.6.9, SF9.4. Picture Desk, The: figure. 2.2.4. Ralph Kiesewetter © 2004: provided with courtesy, figure. 6.3.19. Richard Thrift © 2004: provided with courtesy, figure. 6.3.11. Steve Axford © 2003: provided with courtesy, figure. 6.3.5. United Media Syndicate, Inc © 1974: figure.1.6.1. University of Queensland /Chris Stacey © 2003: figure. SF 7.4. U. S. Geological Survey: figure. 6.3.2b; Robert E. Wallace © 2004, figures 3.4.1, 9.1.3. Walter & Eliza Hall Institute: provided with courtesy, figure. SF4.5. West Australian, The: provided with courtesy, figure. 7.5.1.

Every effort has been made to trace and acknowledge copyright. However, should any infringement have occurred, the publishers tender their apologies and invite copyright owners to contact them.

The Science Focus series has been written for the NSW Science syllabus, stages 4 and 5. It includes material that addresses the learning outcomes in the domains of knowledge, understanding and skills. Each chapter addresses at least one prescribed focus area in detail. The content is presented through many varied contexts to engage students in seeing the relationship between science and their everyday lives.

Coursebook The coursebook consists of nine chapters with the following features. Chapter opening pages include: • the key prescribed focus area for the chapter • outcomes presented in a way that students can easily understand • pre quiz questions to stimulate interest and test prior knowledge. Chapter units open with a ‘context’ to encourage students to make meaning of science in terms of their everyday experiences. The units also reinforce contextual learning by presenting theory, photos, illustrations and ‘science focus’ boxes in a format that is easy to read and follow.

Each PFA has one special feature which uses a contextual approach to focus specifically on the outcomes of that PFA. Student activities on these pages allow further investigation and exploration of the material covered.

Each unit ends with a set of questions. These begin with straightforward ‘checkpoint’ questions that build confidence, leading to ‘think’, ‘analyse’ and ‘skills’ questions that require further thought and application. Questions incorporate the syllabus ‘verbs’ so that students can begin to practise answering questions as required in examinations in later years. The extension questions can be set for further exploration and assignment work and include a variety of structured tasks including research, creative writing and internet activities suitable for all students. Extension questions cater for a range of learning styles using the multiple intelligences approach, and may be used for extending more able students.

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Key numeracy and literacy tasks are indicated with icons. Practical activities follow the questions. These are placed at the end of the unit to allow teachers to choose when and how to best Prac 1 incorporate the Unit 1.2 practical work. Cross references to practical activities within the units signal DYO suggested points for practical work. Some practical activities are ‘design-your-own’ (DYO) tasks. Chapter review questions follow the last unit in each chapter. These cover all chapter outcomes in a variety of question styles to provide opportunities for all students to consolidate new knowledge and skills.

The use of the Aboriginal flag in the coursebook denotes material that is included to cover Aboriginal perspectives in science.

Companion Website The companion website contains a wealth of support material for students and teachers, which has been written to enhance the content covered in the coursebook.

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Online review questions Auto-correcting chapter review questions can be used as a diagnostic tool or for revision at school or home, and include: • multiple choice • matching • labelling • fill in the blanks. Results can be emailed directly to teacher or parents.

Destinations A list of reviewed websites is available— these relate directly to chapter content for students to access. Technology applications These are activities that apply and review concepts covered in the chapters. They are designed for students to work independently, and include: • animations and Quicktime Video to develop key skills and knowledge in a stimulating, visual way • drag and drop activities to improve basic understandings in a fun way • technology activities to enhance the learning of content in an interactive way.

Homework Book

Teacher resource centre

The homework book provides a structured program to complement the coursebook. These homework activities: • cover various skills required in the syllabus. • offer consolidation of >>> key content and HOMEWORK BOOK interesting extension activities. • provide revision activities for each chapter, including the construction of a glossary. • cater for a multiple intelligences approach through varied activities. • have ‘Worksheet’ icons in the coursebook to denote when a homework activity is available.

A wealth of teacher support material is provided and is password protected and includes: • a chapter test for each chapter, in MS Word to allow editing by the teacher. • Coursebook answers. • Homework Book answers. • Teaching programs.

Kerry Whalley Geoff Phillips Greg Rickard Stewart Monckton

Worksheet 1.3 Observing and measuring

Teacher resource pack Material in the teacher resource pack consists of a printout and electronic copy on CD. It includes: • curriculum correlation grids mapped in detail to the NSW syllabus. • chapter-based teaching programs. • contextual teaching programs. • Coursebook answers. • chapter tests in MS Word. • Homework Book answers.

Worksheet 4.6 Sci-words

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Verbs Science Focus 1 uses the following verbs in the student activities. Account

state reasons for, report on

Identify

recognise and name

Analyse

identify components and the relationships among them; draw out and relate implications

Investigate

plan, inquire into and draw conclusions

Justify

support an argument or conclusion

Apply

use, utilise, employ in a particular situation

List

Assess

make a judgement of value, quality, outcomes, results or size

write down phrases only without further explanation

Modify

change in form or amount in some way

Calculate

determine from given facts, figures or information

Outline

Clarify

make clear or plain

sketch in general terms; indicate the main features of

Classify

arrange or include in classes/categories

Predict

Compare

show how things are similar or different

suggest what may happen based on available information

Construct

make; build; put together items or arguments

Present

provide information for consideration

Contrast

show how things are different or opposite

Produce

provide

Draw

draw conclusions, deduce

Propose

Demonstrate

show by example

Describe

provide characteristics and features

put forward (e.g. a point of view, idea, argument, suggestion) for consideration or action

Design

provide steps for an experiment or procedure

Recall

present remembered ideas, facts or experiences

Discuss

identify issues and provide points for and/or against

Recommend

provide reasons in favour of

Distinguish

recognise as being distinct or different from; note differences between

Record

store information and observations for later

Evaluate

make a judgement based on criteria; determine the value of

Research

investigate through literature or practical investigation

Examine

inquire into

Select

choose one or more items, features, objects

Explain

relate cause and effect; make the relationships between things evident; provide the ‘why’ and/or ‘how’

Specify

state in detail

State

provide information without further explanation

Summarise

express concisely the relevant details

Use

employ for some purpose

Gather

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collect items from different sources

Science Focus 1

A fully mapped and detailed correlation of the stage 4 curriculum outcomes is available in the Science Focus 1 Teacher Resource Pack.

Stage 4 Syllabus Correlation

chapter

1 23456789

outcomes

Being a Scientist 4.1

Solids, Liquids and Gasses

Mixtures and their Separation

Cells

Heat, Light Classification and Sound

Forces

▲

▲

4.2

▲

4.3

•

▲ ▲

▲

•

4.4

▲

▲

4.5

▲

•

4.6

•

4.7

Our Planet Earth

▲

•

▲

Earth and Space

•

• •

4.8

• •

4.9

•

•

4.10 4.11

• • • • • • • • • • • •

4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19 4.20 4.21 4.22 4.23

• • • • • • • • • • •

• • • • • • • • • • •

• • • • • • • • • •

• • • • • • • • • • •

• • • • • • • • • • •

• • • • • • • • • • •

• • • • • • • • • • •

• •

• • •

4.24

•

4.25

•

4.26

• •

• •

•

4.27 Note:

•

• • • • • • • • • • • •

•

▲ indicates the Key Prescribed Focus Area covered in each chapter. Chapters may also include information on other Prescribed Focus Area’s..

1

Being a scientist Key focus area:

4.13, 4.14, 4.2

Outcomes

>>> The nature and practice of science By the end of this chapter you should be able to: identify pieces of equipment commonly used in science use equipment to safely and efficiently perform simple tasks collect and record data and display it in tables, graphs and diagrams with the correct units follow procedures and write reports for simple experiments

Pre quiz

describe ways to reduce the risk of accidents while working in a laboratory.

1 Identify some of the dangers you may meet in the science laboratory. How might you avoid them?

2 What do you think science is? 3 Name as many types of science equipment as you can.

4 What should a report about a science experiment tell the reader?

5 A metre is one of the metric units used in science. Identify some more.

6 Who invented the Bunsen burner?

7 What does the word ‘variable’ mean?

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1

UNIT

context

1.1 In science you will need to deal with many potential dangers. You will work with intense heat, acids and other corrosive substances. It is particularly dangerous if any chemicals get splashed into your eyes. Other chemicals are poisonous and can make you extremely ill or can kill. Broken glass and equipment pose the risk of cutting you or of fragments entering the eye if they shatter.

Fig 1.1.1

Before we can start any science we must agree on a set of laboratory safety rules. These rules will assist us in reducing any dangers.

The figure below shows some situations where students are doing something potentially dangerous. Can you identify the dangers? What rules would you make to prevent these dangers happening?

What’s wrong?

In the figure below, the students are doing the right thing. Can you identify what they are doing right? What’s right?

Fig 1.1.2

When working in a science laboratory always look for unsafe activities and report these immediately to your teacher.

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Safety–before we start

UNIT

1.1

[ Questions ]

Checkpoint

Skills

1 Copy the following into your workbook. Modify any incorrect statements so they become true. a It is OK to pour all substances down the sink after an experiment. b Running and pushing people in the laboratory is never allowed. c It is OK to eat and drink in the laboratory. d Spilt chemicals can be left unattended. e The teacher must always be told if something goes wrong. f All solid objects should be put in the bin and not down the sink. g Safety glasses are optional when we use chemicals in the laboratory. h Chemicals should never be tasted or smelled. i To investigate a reaction in a test tube, look straight down the tube. j Always point test tubes away from yourself and others. k It is good science to mix unknown chemicals together.

9 Without using any words, design a simple two-colour sign to tell people that: a there is a slippery surface ahead b crocodiles are in the waterways c you should not eat centipedes d earmuffs must be used in this area e fruit is good for you

2 Describe four dangers that you might have to deal with in a science laboratory.

Think 3 Compare the dangers that appear in science with the dangers that appear in other subjects such as: a design and technology b food technology c PDHPE 4 Explain why safety rules in science might be different to the rules in other classes. 5 Identify five injuries that can happen in a science laboratory if simple safety rules are not obeyed. 6 Suggest a way of reducing the risk of those injuries occurring. 7 Eye injuries are common in science laboratories. Describe two ways that eye injuries could occur and suggest how to minimise the risk of these injuries. 8 Make a list of ten safety DOs and ten DON’Ts in the laboratory.

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10 Design a series of simple signs to inform students of the science safety rules. The signs must be in two colours only and use only a few words.

[ Extension ] Skills 1 Construct a time line showing the dates for the invention of the following: a steam locomotive b aeroplane c jet aircraft d refrigerator e telephone f television g electric light bulb h telegraph i X-ray machine j satellite k computer l personal computer m record player or phonograph n CD player o VCR p DVD player q laser

Investigate 2 Find and draw the symbols commonly used to label these types of chemicals: a flammable b corrosive c explosive

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3 Define these terms: a toxic b spontaneous combustion c caustic d flammable

7 Select two scientists from the table, one from each group.

4 Draw what you think would be good symbols for the terms used in question 3. 5 Find and draw the signs commonly used for the following: a an information sign showing that this is a wheelchair toilet b a warning sign that eye protection should be worn 6 What do you think these signs or labels mean?

a

c

e

UNIT

1.1

b

d

a Describe his or her work. b Explain why the scientist’s work was an important development for science or society in general. c Identify dates that were important in the scientist’s life. Record reasons why these dates were important. d Present your information as either a poster, a Powerpoint presentation or a diary as if written by the scientist.

Group A International

Group B Australian

Marie Curie

Karl Kruszelnicki

Galileo Galilei

William Bragg

Robert Gallo

Frank Macfarlane Burnet

Stephen Hawking

John Cornforth

Alfred Nobel

Peter Doherty

Rosalind Franklin

Howard Florey

Isaac Newton

Fred Hollows

William Herschel

Mark Oliphant

Luc Montagnier

Andy Thomas

Charles Darwin

Sister Elizabeth Kenny

Albert Einstein

Barry Marshall

Ernest Rutherford

Tim Flannery

Thomas Edison

Sir Gustav Nossal

James Watson

David Unaipon

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Fig 1.1.3

5

UNIT

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context

1. 2 Scientists ask questions about how the physical and living world around us works. These might be: • Why does water turn white when it goes down a waterfall? • How do ants breathe? • How are rainbows formed? • What affects the rate at which fruit rots? • Why are sunsets red? • Why are dead cockroaches always on their back?

Physics

Biology

Chemistry

Geology

Astronomy

Ecology

Science—asking questions The answers to these questions could be found in textbooks, encyclopaedias or on the Internet. Sometimes the questions that scientists ask have never been asked before and that is when scientists need to find the answers themselves by performing experiments. An experiment is simply a test on a small part of the The branches of science world. Science covers many areas. So many in fact that it is often Scientists need to be easier to split science into able to use all of their five branches or disciplines. Some of senses to make correct the important branches are observations. illustrated in Figure 1.2.1. Physics asks questions about how The main sense a and why things move and the scientist uses is sight. forces and energy involved. They will also use Biology is a branch that asks hearing, smell, taste about living things. Chemistry investigates materials, and touch, although chemicals and chemical reactions sometimes it will be far and how they can be used. too dangerous to use Geology studies rocks, the some of these. Tasting is Earth, earthquakes, volcanoes particularly dangerous and fossils. Astronomy asks about the planets, in science. stars and the universe. In a way, a scientist Ecology studies how living things is like a detective trying affect each other and the environment in which they live. to solve a puzzling case.

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The branches of science

Fig 1.2.1

Clues must be gathered through careful observation of all the evidence. The various clues can then be linked together until a conclusion can be drawn about the case. In science we don’t always get it right the first time—sometimes more experiments and Prac 1 p. 8 observations are required.

UNIT

1. 2

UNIT

1.2 [ Questions ]

Checkpoint 1 Identify and name the five senses that we can use to make observations. 2 List four of the main branches of science.

Think 3 We can use all our senses to make observations but sometimes it is too dangerous to use some of them. Complete the table below.

Experiment

Senses that you would use

4 Identify which branch or discipline of science these scientists would be working in: a Johanna is studying the eating habits of a cheetah. b Yianni is developing a new plastic. c Josh is measuring the growth rate of an apple tree. d Brigid is studying the movement of the planets. e Lauren is studying the crystals embedded in a rock. 5 ‘Scientia’ is the Latin word for knowledge. Describe the sort of knowledge that scientists research.

Sense that would give the most information

Senses that you would NOT use

Testing the ability of strong acids to clean a sheet of metal Testing how long milk takes to go off Testing how long it takes for six tomatoes to ripen Studying lava flowing from a volcano Testing a new pesticide

[ Extension ] Create 1 Design a game suitable for primary students to teach them about the branches of science. 2 Create a website that explains the branches of science. Hyperlink the main and sub-branches to show the relationship between different areas of science.

Investigate 3 Research what these sub-branches of science study. a botany b microbiology c palaeontology d acoustics e seismology 4 Identify whether these sub-branches of science belong in physics, chemistry, biology, geology or ecology. a optics: the study of light b entomology: the study of insects c vulcanology: the study of volcanoes d zoology: the study of animals

5 Scientists use a lot of abbreviations. Identify what the following abbreviations stand for. a mL f HIV+ b CSIRO g mm c HAZCHEM h NASA d kg i UNESCO e µ j π

Action 6 Interview 20 people to find out what they know about the branches of science. To do this: a Prepare a list of six questions to ask your subjects. b Present the information collected in the form of a table.

Surf 7 Find out more about the branches of science by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 1 and clicking on the destinations button.

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What is science?

UNIT

1. 2

[ Practical activity ] The mysterious case of the stolen sausages

After a beautiful sunny morning, the weather on this fateful day has turned terrible, with torrential downpours of rain and howling wind. You arrive home at 3.17 p.m. and are surprised to notice that the neighbour’s lawn has been mowed. You are surprised, since from experience you know that wet grass is very hard to cut. You enter the house. The sausages that you left defrosting on the kitchen table are gone! You enter the lounge room. The front window has been shattered! Pieces of broken glass lie everywhere. There is now nothing interrupting the view of next door’s garden and lawn. Mum’s favourite vase on the mantelpiece is lying in pieces Prac 1 Unit 1.2

on the floor. You remember that every time your neighbour dropped in she always said, ‘Why don’t you get rid of that old vase … it’s so ugly!’. The curtains are all messed up and the carpet is soaking wet and marked and smudged with mud! Some strands of blond hair are stuck on the windowsill. But what’s this? A small stone has been placed in the middle of the coffee table … the calling card of the sausage burglar? Later that night you notice that Fritz, the golden retriever, hasn’t touched the food in his bowl. Your mission is to discover all the details of this mysterious case … who, when, why and how!

Questions 1 State what you want to know about the case. Scientists call this the ‘aim’. 2 List the observations you have made. 3 Identify the suspects in this case. 4 Explain what evidence there is to link them to the crime scene. 5 In conclusion, identify: a who you think stole the sausages b who or what broke the window c when it probably happened d who or what broke the vase e the order it all happened in. In the above case, you have used many of the skills a scientist needs. To have successfully solved the case you needed to: • be clear about what you were trying to find out • make an educated guess of what you hoped to find out • make careful observations of what happened • take careful measurements if possible • infer reasons about why the investigation went as it did • draw logical conclusions about what was found out.

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The clues!

Fig 1.2.2

UNIT

context

1. 3 Every one of us is a scientist already, since we are constantly observing and interacting with the world around us. To be a good scientist we must use these observations to think about what is happening.

Observation: Inference: Prediction:

Observations—qualitative vs quantative Scientists make two types of observations. Sometimes observations are qualitative, being written down in words only. Qualitative observations would be made about the noise a bird makes, the taste of ice-cream or the fact that bubbles appear when the top of a soft drink bottle is unscrewed. Other observations are quantitative. These observations involve measurements and are stated as numbers. Examples are the temperature of a room recorded as 25°C, the time being 12.45 pm or the volume of a liquid in a Prac 1 can of Coke being measured as 375 mL. p. 11

Inferring and predicting From your observations, you can make an inference, or logical explanation, about what happened and why it happened. You may then be able to predict how it could work in the future. Predictions must be

UNIT

1. 3

logical and based on the observations made in your earlier experiments. You make observations, inferences and predictions every day, probably without knowing it:

[ Questions ]

Checkpoint 1 Copy the following into your workbook and modify any incorrect statements so they become true. a A qualitative observation is one where numbers are involved. b If we use a thermometer, we are making qualitative observations. c The colour of a leaf is an example of a quantitative measurement.

The dog barked. That possum is back again. The barking will frighten it away.

Sometimes the same observation can lead to different inferences and predictions: Observation: Inference: Prediction: or: Observation: Inference: Prediction:

The leaves are turning brown. The tree is dying. I will have to get a new one. The leaves are turning brown. It is a deciduous tree that loses its leaves in autumn. It will get new leaves in spring.

A calendar may assist you in deciding which is correct. d An inference is a logical explanation about what happened in an experiment. e A prediction is a logical guess about what might happen in the future. 2 List four observations about samples of: a sugar b water c talcum powder d a $1 coin e the gas we breathe out

Think 3 Label each sentence below as an observation, inference or prediction. a The missing fish were eaten by the cat. There will be no fish left in the pond after a while. The cat is on the edge of the fishpond. b One Olympian is bigger than the other. The bigger Olympian will win the event. One can lift a heavier weight than the other can.

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Observing c The fish will be a big one. I’ve caught a fish. The line is taut and the fishing rod is bending. Fig 1.3.1

4 The gas we breathe out contains carbon dioxide. Identify this statement as an observation or prediction.

Analyse 5 Jill is doing the wrong thing in the diagram below. Before Jill passed out, she wrote down everything that she saw, heard and smelt in this experiment.

6 While in hospital, Jill made some inferences and predictions about the experiment. Identify which are inferences and which are predictions. a A chemical reaction happened between the copper and the acid. b The dissolved copper turned the liquid green. c The reaction caused the brown gas. d A different acid might not produce brown gas. e A different metal might not dissolve. f Brown gas makes people pass out. g More copper would have made more brown gas. h Stronger acid would give us more brown gas. 7 Without looking up from this page: a Identify how many separate windowpanes there are in this room. b Describe the colour of your parents’ eyes. c Describe the colour and type of shoes your teacher is wearing today. d Accurately draw the Australian flag. e Identify how many kangaroos there are on the $1 coin. f Draw a map showing how to get from the laboratory to your locker. 8 Below is a drawing of fossilised dinosaur footprints. Describe any observations that can be made about: a the size of each footprint b the spacing of the footprints

Describe any observations that Jill would have made.

copper

acid

Fig 1.3.2

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Fig 1.3.3

something something smells! smells!

9 State inferences that can be made about: a the number of creatures present b the speeds of the creatures

UNIT

1.3 One scientist inferred that the larger dinosaur chased and ate the smaller one. 10 Identify where on the diagram you think: a the large dinosaur entered the picture b the small dinosaur began to run c the larger dinosaur caught the smaller one d the larger dinosaur first saw the smaller one e the smaller dinosaur realised it was being hunted 11 State an inference about whether the larger dinosaur was carnivorous (meat eating) or herbivorous (plant eating). 12 Are you sure which dinosaur was the largest? Have you made an observation or inference here?

[ Extension ] Investigate 1 At home (or out of class), write a description of your teacher with sufficient detail to allow another person to identify them in a line-up. Include the clothes they were wearing when you last saw them. 2 Go outside and feel the weather. Write a description of what it is like without using any of the words normally used to describe weather, like rain, wind, temperature etc.

13 Describe what you think happened to the dinosaur with the smallest feet. Is this an observation or an inference? 14 Infer what else could have happened to this dinosaur.

UNIT

1.3

[ Practical activity ] The burning question!

1 Melt a little of the wax at the bottom of the candle and use it to stick the candle to the lid or petri dish.

Aim To observe a burning candle Prac 1 Unit 1.3

Method

Equipment A candle, gas jar or beaker, metal or plastic lid or petri dish, matches, access to electronic scales

2 Weigh the candle and lid or dish on the electronic scales. Record your result. 3 Light the candle. 4 Use all your senses (except taste) to write as many observations as you can. (Michael Faraday, the nineteenth-century scientist, made 53!) 5 Now cover the candle with a gas jar or beaker. 6 Record more observations. 7 Weigh the candle and lid again.

Questions 1 How many different observations did you make? For each observation, state whether it was qualitative or quantitative. 2 Compare the two weights. If they were different, explain why.

Fig 1.3.4

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UNIT

context

1. 4 When we do a job we usually use equipment to make the job easier. It is the same in science. We use equipment to help us carry out experiments and to make more accurate observations. Some equipment is used to take accurate measurements in an experiment.

Thermometers are used to measure temperature. Stopwatches and electronic timers are more accurate than normal watches and clocks, and can be used for better timing. Other equipment magnifies very small objects that might normally be difficult to measure. Microscopes magnify extremely small objects, while telescopes magnify objects that are far away. Microphones and electronic amplifiers allow us to hear sounds that can otherwise not be heard.

Everyday laboratory equipment In the school science laboratory, you will use a lot of equipment. As with all equipment there are special rules for using each item. Your teacher will instruct you on how to safely use each one. Some that you will use are shown in Figure 1.4.1. Worksheet 1.1 Science equipment wordfind Worksheet 1.2 Identifying science equipment

Scientific drawing Diagrams of scientific equipment must be easy to draw and easy to read. You need not be an artist but you do need to follow conventions so that your

250

spatulas

230

thermometer

210 190 170 150

beaker

130

measuring cylinder

110 90

test tube

conical flask

70

watch-glass

50 30

to measure out materials

clamp

bosshead

or to take accurate measurements

or to run experiments in

test tube rack with drying posts

safety glasses

retort stand tongs

clay triangle

Fig 1.4.1

12

or for holding things

Laboratory equipment

or for keeping us safe

diagrams can be understood by another scientist. Scientists draw their equipment as a cross-section: they ‘split’ the equipment down the middle. The drawings are simple lines and curves, normally without any shading or colouring. Figure 1.4.2 shows how scientists draw some of the most common equipment used Prac 1 in the laboratory. p. 14

UNIT

1. 4

Fig 1.4.2

UNIT

1. 4 Drawing scientific equipment

Pyrex

Pyrex

[ Questions ]

Checkpoint 1 Identify the glass-like substance from which many pieces of science laboratory equipment are made. (Hint: the name is often printed on the sides of beakers and flasks.) 2 Copy the following and modify any incorrect statements so they become true. a A clay triangle is used to hold a watch-glass over a Bunsen burner. b Beakers are used for accurate measurement of liquids. c Conical flasks are useful for chemical reactions. d Test tubes are used for heating small amounts of liquids. e Thermometers are used to stir liquids.

Think 3 Identify a piece of equipment that you would use to: a measure the temperature of boiling water b measure out exactly 55 mL of salt water c support a thermometer in a beaker d transfer a small amount of solid onto a balance e pour a liquid into a conical flask 4 Identify a piece of equipment that you would need to make a good set of observations in the following: a A plant is to be grown from seed. b Yeast releases a lot of heat when it is used in the fermentation of grapes. c Germs are being studied in a hospital. d The planet Mars is to be studied. e The speed of an athlete in a 100 m sprint is to be studied. 5 Describe the similarities between: a a beaker and a flask b a beaker and a measuring cylinder c tongs, a peg and a clamp d a clay triangle and a gauze mat e a test tube and an evaporating dish

filter paper and funnel

test tube

beaker

conical flask

6 Name a piece of equipment that would assist the following scientists in making their observations. a A microbiologist wants to study extremely small bacteria that have been causing infections. b A chemist is measuring the heat generated by a chemical reaction. c A physicist wants to accurately measure the time it takes for a stone to drop 2 m. d A botanist wants to measure the growth rate of a young tree. e An electrical engineer wants to measure the current flowing in an electrical circuit. f An astronomer wants to study the surface of the Moon. 7 State where the following special safety equipment is located in your school laboratory. a fire blanket b fire extinguishers (is there more than one type?) c gas control switch d electrical master switch e eyewash f broken glass container g bucket (maybe with sand or another chemical to soak up spills) h first aid cabinet i warning and safety signs

Skills 8 Draw a diagram representing a: a beaker b conical flask c test tube

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Equipment

9 Draw a plan or bird’s-eye view of the laboratory you are in, showing the location of all the special safety equipment. An example is shown in Figure 1.4.3.

[ Extension ] Investigate

main gas tap

1 Research what these pieces of equipment look like and how they are used. Draw a scientific diagram of each. a pipette f Geiger counter b burette g vernier calliper c micrometer h barometer d mortar and pestle i sphygmomanometer e ammeter and j thermistor and voltmeter thermocouple

fire extinguisher bucket of sand

sink

teacher’s bench

2 Ask your teacher for a scientific supply catalogue. a Draw four pieces of equipment that are not commonly used in the school laboratory. b Describe the use of each piece of equipment in part a.

emergency exit cleaning cloths in cupboard

Action

sink emergency exit

3 Visit a pharmacy and ask the chemist what equipment they use to make their preparations. Compare the equipment the chemist uses to what is available in the school laboratory.

first aid cabinet

Fig 1.4.3

Create 4 Use animation software to animate different pieces of laboratory equipment showing how they are used.

UNIT

1. 4

[ Practical activity ] What is it?

Prac 1 Unit 1.4

Measuring equipment

Pouring equipment

Storage equipment

Aim To draw, classify and name common laboratory equipment

Equipment to run chemical reactions in

Equipment A range of scientific equipment

Method 1 Divide a new page in your science workbook into a table with eight sections, as shown opposite. 2 Every piece of equipment you have been provided with must be drawn under one of the headings. Draw each piece: a as realistically as you can b in the proper scientific way Write the name of each piece of equipment under the diagram.

14

Safety equipment

Holding equipment

Cleaning equipment

Mixing equipment

UNIT

Scientists need to record their information accurately so that others can repeat their experiments. To do this, they write a scientific report. A report is not a story and it is not a set of instructions. It tells the reader what happened.

A report should contain subheadings for the following sections: • aim • hypothesis (optional) • equipment or materials • method • results and observations • discussion or analysis • conclusion.

Aim This is what you intended to do in the experiment.

Hypothesis (optional) Scientists always have an idea of what they think may happen or what they might find out in an experiment. Their ‘educated guess’ is called a hypothesis.

Equipment or materials All important equipment and chemicals needed in the experiment must be included. The sizes of the various pieces of equipment must also be included.

Method This is a detailed list of what was done in the experiment. To allow another scientist to be able to repeat the experiment, you must include what quantities were used and the exact order in which the experiment was performed. A diagram of the experiment (with all the equipment connected, not separate) can be very useful.

Results and observations

Headings and units (for example g, kg and t) are necessary.

Discussion or analysis This is where scientists discuss: • any problems encountered in the experiment and what was done to overcome those problems • what you think your results show about the experiment • what you have found about the experiment from other sources such as textbooks, the Internet or encyclopaedias. It can also include: • graphs • ideas for further experiments.

Conclusion This is where scientists summarise what they have found out in the experiment. The conclusion should be short and must relate to the aim.

1. 5 UNIT

context

1. 5

Prac 1 p. 17

[ Questions ]

Checkpoint 1 In your own words, describe what is meant by the term ‘aim’. 2 Explain how a hypothesis is different to an inference. 3 State the meaning of the word ‘tabulated’. 4 Identify two things that must always be included in result tables. 5 State two things that graphs must have on their axes.

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You must include a complete list of measurements and observations you took in the experiment. It is usually clearer if the measurements are displayed in a table.

15

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Reporting

Date?

Apparatus? Materials?

No label What weights?

What length?

Spacings should be equal, and increase by the same amount

Points are too big No units

How was it measured?

Put units in headings

A diagram would help here

What was actually found out here?

Units changed

Units changed The conclusion does not match the aim

Tony’s report

Fig 1.5.1

Analyse Tony wrote the above report on an experiment he ran on the flexibility and stretch of a fishing line. 6 Describe Tony’s conclusion.

16

10 Describe two things that need to be added to Tony’s results table. 11 State one thing that needs to be added to the graph in the report.

7 Identify which section in Tony’s report on the flexibility of fishing line is missing.

12 Explain whether the aim and the conclusion match.

8 Tony’s hypothesis was excellent. Explain why.

13 Propose a better conclusion for this experiment.

9 In the report the reader needs to guess some things if they are to repeat the experiment. List the things that the reader may need to guess in order to do the experiment.

14 For the detective investigation in Unit 1.2, state: a the aim c your results or observations b your hypothesis d your conclusion

[ Extension ] 1 Design and carry out an experiment to see what type of soap solutions make the biggest soap bubbles. Use the headings of aim, hypothesis, method, results and conclusion in your report. Identify the variables that you are using and explain how you control them. DYO

[ Practical activity ]

5 Add another drop of water, being careful to keep it the same size, and estimate the area covered. 6 Repeat for three drops. 7 Predict the size for 4, 5 and 6 drops. 8 Check your predictions by counting the squares for 4, 5 and then 6 drops on the slide.

Questions 1 Compare the actual area to your predicted area and comment on your prediction. 2 Describe any pattern you see connecting the number of drops with the area covered.

Spreading puddles Aim To measure the area of water droplets Prac 1 Unit 1.5

4 Estimate the area covered by the drop by counting the squares on the graph paper underneath. Count half-covered squares as full and less than half-covered as empty.

Equipment Glass microscope slide, eyedropper, graph paper

3 Predict the size for 7, 8, 9 and 10 drops. 4 Present your results as a line graph, with area on the vertical axis and the number of drops on the horizontal axis.

Method 1 Construct the table below in your workbook. Number of drops

1

2

3

4

5

6

7

8

9 10

Predicted area (squares) 100

Actual area

2 Collect a clean glass slide, an eyedropper and a piece of graph paper and place the graph paper under the slide. 3 Drop one drop of water onto the slide. How big is the drop?

Area (squares)

UNIT

1. 5

UNIT

1.5

80 60 40 20

Fig 1.5.2

eyedropper

0

1

2

3

4 5 6 7 Number of drops

8

9

10

Fig 1.5.3 5 State a conclusion for this experiment.

graph paper

glass microscope slide

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UNIT

context

1. 6 Measurements are extremely important in science. They improve the accuracy of our observations and allow us to see any patterns that may exist.

Scientists use units from the metric system for their measurements. Grams are used for measurements of small masses, like the mass of a coin or a mouse. Kilograms or tonnes are used for heavier objects. Centimetres, metres and kilometres are used for length, and seconds, minutes and hours for time. Worksheet 1.3 Observing and measuring Worksheet 1.4 Metric units of measurement

A mistake is something that can be avoided with care. Errors are not mistakes, but are slight changes in measurements that cannot be avoided regardless of how careful you are. A reading error is always made when we need to guess the measurement because it falls between markings.

Whoops! In 1999 NASA sent three space probes to land on and explore the surface of Mars. All three failed. One is thought to have failed because NASA scientists did not write the units down for a series of measurements. One group of scientists thought the measurements were in older imperial units, while another group thought they were metric. This caused the calculated altitude of the spacecraft to be below ground level, so the spacecraft crashed into the surface!

Measurement

Commonly used metric units

Abbreviations

Length, height and distance

millimetre, centimetre, metre, kilometre

mm, cm, m, km

Mass (sometimes incorrectly called weight)

milligram, gram, kilogram, tonne

mg, g, kg, t

Time

second, minute, hour

s, min, h

Speed

kilometres per hour, metres per second

km/h (sometimes shown on roadsigns as kph), m/s

Volume of a liquid

millilitres, litres, megalitres

mL, L, ML

Temperature

degrees Celsius, kelvin

°C, K

Fig 1.6.1

18

How do I take accurate measurements?

What do you notice about the American spelling of centimetres?

UNIT

1.6 70 mL

70 mL

65

65

60

60

55

55

50

50

30°C

20°C

10°C

reading = 67 mL

Fig 1.6.4 Fig 1.6.2

Prac 1 p. 22

We cannot always be sure of measurements exactly—for example, is the temperature shown here 23.4°C, 23.5°C or 23.6°C?

Another important error is caused by not having your eye directly in line with the measurement. This is called parallax error. Parallax error—who is reading it correctly, A, B or C? B

A

0

5

10

15

Fig 1.6.3

C

20

25

30

35

A common problem when using measuring devices is called zero error. This is when the device reads some value even though nothing is being measured. An example is a weighing scale that measures 0.12 kg when nothing is on it.

reading = 66 mL

The meniscus in a measuring cylinder—for water the meniscus curves up at the edges, and for mercury it curves down at the edges.

Curvy water Liquids in narrow tubes such as measuring cylinders often have a curve at their surface. This curve is called a meniscus and it gives us a problem when we need to measure the volume. Measure from the bottom of the meniscus if it curves downwards. Measure from the top of the meniscus if it curves upward.

To minimise errors, scientists need to follow these rules or conventions: • Always read measuring devices from directly in front. • Always check that the measuring device has the correct starting point, such as zero. • Always write down measurements as soon as they are taken. Do not try to remember measurements. • Always write down the units of the measurements. • Always use correct abbreviations for units. • If possible, write all measurements in a table. • Do not use fractions such as 1/2 or 1/4 in measurements. Use decimals instead. For example, 9.5 kg is acceptable, 91/2 kg is not. • If you are working in a group, always make sure you have a copy of the results before you leave the laboratory. • Always measure quantities in metric Prac 2 p. 23 units.

An important measuring device: the beam balance A beam balance is often used in the school laboratory to measure the mass of an object. The mass is a measure of how much matter there is in an object and is sometimes incorrectly called weight.

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Measurement

Fig 1.6.7

0

100

200

300

400

500

600

0

10

20

30

40

50

60

70

80

90

100

1

2

3

4

5

6

7

8

9

10

0

Fig 1.6.5

An electronic balance

A laboratory beam balance is used for measuring mass.

Fig 1.6.6

A beam balance reading 200 + 70 + 3.5 = 273.5 g

0

100

200

300

400

500

600

0

10

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30

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50

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0

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UNIT

1. 6

20

[ Questions ]

Mass is usually measured in the laboratory in grams, abbreviated as g, or kilograms (kg). For increased accuracy an electronic balance is sometimes used.

Prac 3 p. 23

Checkpoint 1 Copy the following, and modify any incorrect statements so they become true. a Metric units are never used by scientists for measurements. b The kilometre is an example of an imperial unit. c Seconds could be used to measure the distance a sprinter runs. d There is 375 ML in a normal soft drink can (be careful). e Mistakes are the same as errors.

2 Draw a picture or cartoon showing each of the rules for taking measurements. 3 State a reason for each of the above rules for taking measurements. 4 State the correct metric unit for mass. 5 State two important types of errors. Give examples of each.

Think 6 Select a unit of measurement and a device that you would use to measure the following quantities. a b c d e

14 Read these measuring devices and state their measurements. Fig 1.6.9

the temperature of a fishpond the height of a person the length of a bull ant the mass of a teaspoon of sugar the volume of a glass of orange juice

a

7

b

c

d

6

40

300

30

200

20

100

10

5 30

4 3

7 Identify what is wrong with these measurements. a Mass of a mouse = 1501⁄4 g b The car was travelling at 100. c The wind speed was 10 miles per hour. d A full bottle of soft drink contained 1.25 mL. e Evan’s height = 168 m. 8 Natalie took note of the speedometer reading every 5 seconds as her mum’s car accelerated. At the start, the speed was 0 km/h. The speed was 20 km/h after 5 seconds, then 30, 50, 60 and 80 km/h every 5 seconds after. Collate these results into a table. 9 Identify which of the abbreviations are correct for each measurement unit. a gram: gm gms G g b kilogram: kilo kg Kg KG c millimetre: mms mm Mm mL d litre: lt mL lit L e kilometres per hour: kph km/h km/hr kil/h f minutes: min m mins ms g degrees Celsius: deg C deg °C C h hour: hr h Hr H I seconds: sec secs S s

20

e

f

2

0

100

200

300

400

500

600

0

10

20

30

40

50

60

70

80

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100

0

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9

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600

0

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100

0

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8

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g

h

60

30

j

0

300

i

16

17

900

0

18

100 200

800 700 600

11 Describe what will happen to the needle of a beam balance if too much sliding mass is added.

20

Fig 1.6.8

200

k

50 40

12 Describe the difference between an error and a mistake.

100 15

45

10 Sometimes people use an incorrect term for mass. Name this incorrect term.

Skills

UNIT

1.6

500

300 400

l 10 0

55 0 50

5

10

45 15 40 20 35 30 25

13 Rob’s poorly recorded results for an experiment are shown here. Draw up a table and present the results as they should look.

21

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Measurement

[ Extension ] Investigate

Action

1 Identify whether NASA made an error or a mistake in its failed 1999 missions to Mars. Explain your reasoning.

3 Describe how you would find out each of the following. Then use your method to measure them. a the mass of a Smartie or an M&M without using any weighing device b the thickness of a piece of A4 paper with a normal ruler DYO c the number of your heartbeats in a minute

2 Fred measured the mass of some substances that could not be held in the pan of a beam balance. He needed to put the substances in containers instead. Complete the table of his results.

Type of empty container Folded piece of paper Watch-glass

Mass of container

Type of substance that was added

Mass of container + substance

1.2 g

Salt

34.5 g

13.7 g

Crystals

Beaker

UNIT

Prac 1 Unit 1.6

275.0 g

195.1 g

[ Practical activities ] Taking measurements

Questions

Aim To measure various items with a range of measuring devices

1 Compare all the results on the paper from each group and state any differences.

Equipment

2 If you got all different measurements, does this means that everyone is wrong?

Access to a range of instruments and pieces of equipment that all show different quantities.

Method 1 Construct a table similar to the one below, in your workbook. 2 Write your measurement in your table and on a piece of paper next to each piece of equipment.

Name of piece of equipment

22

18.6 g

Water

1. 6

Mass of substance

What is being measured

3 Identify any results that were significantly different from the rest. 4 State a conclusion for this experiment. 5 Suggest reasons why scientists may not get exactly the same results.

My measurement

Unit it is measured in

UNIT

1.6 How massive? Prac 2 Unit 1.6

Aim To correctly use a beam balance to find the mass of various objects

5 Repeat this step for all the sliding masses until you finish with the lightest sliding mass.

Equipment

6 When you have successfully got the pointer at 0, record the measurement in your table and on the paper next to each balance.

Access to beam balances and objects to weigh, 50g mass

Method

Questions

1 Construct a table in your workbook with the headings ‘Object being weighed’, ‘Mass’ and ‘Units’.

1 State the reading that should be on a beam balance when nothing is in its pan.

2 At each balance, move all the sliding masses to 0.

2 State the mass that you obtained for the 50 g ‘standard’ mass.

3 The arm should now be balanced and reading 0. If this does not happen, adjust the balance screw on the edge of the arm. 4 Add the object to be measured and slide the heaviest sliding mass until the arm drops below 0. Then pull the sliding mass back one notch.

3 Explain why a 50 g ‘standard’ mass might not be exactly 50 g in an experiment. 4 Describe three errors that might be present in these measurements.

Observations and predictions Prac 3 Unit 1.6

0.7

Aim To find the mass of various lengths of spaghetti

0.6 0.5

4 lengths of uncooked spaghetti, beam balance, ruler with 1 mm markings

0.4

Method 1 Break three lengths of spaghetti each into three pieces of different sizes, so that you end up with nine different lengths. 2 Construct a table in your workbook or set up a spreadsheet with the headings ‘Length’ and ‘Mass’. 3 Measure the length and mass of each piece of spaghetti and record it in your table.

Mass (g)

Equipment

0.3 0.2 0.1 0 10

4 Use this information to draw a line graph and draw a line of best fit through your points or generate the graph using your spreadsheet.

20

30 40 50 Length (mm)

Line of best fit for mass of spaghetti versus length

5 On your graph mark a length that you did not measure.

60

Fig 1.6.10

6 Use the graph to estimate its mass. 7 Get another length of spaghetti and break it at the length you chose in step 5. 8 Measure and record the mass of the spaghetti you used in step 7.

Questions 1 Explain what a line of best fit is. 2 For steps 5–8, compare your predicted value with the actual value. 3 State a conclusion about the link between mass and length of spaghetti.

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UNIT

context

1.7 The work of scientists rarely starts with an experiment but normally with observations made in everyday life or even possibly by accident. Their observations lead them to ask questions like ‘What caused that?’ or ‘Why did that happen?’. They then design experiments to answer their questions.

Joe noticed that when he washed dishes he sometimes made lots of froth and at other times made almost none. Joe has a problem. Let’s see how he solves it scientifically.

only change one factor at a time. These factors are called variables and are anything that may affect an experiment. Joe thought about it carefully and came up with a list of factors that could affect the amount of froth produced: • the amount of detergent used • the amount of water in the sink • the speed of the water coming from the tap • the temperature of the water. These were his variables.

From their observations, scientists can then make a hypothesis. This is a prediction or ‘educated guess’ about what they may find in an experiment or what might have caused the observations.

Prac 1 p. 26

Joe had noticed that more froth was produced when faster tap water was added and when more detergent was used. He thought that these variables would have a great effect but didn’t think the temperature of the water in the sink would have any effect at all. This was his hypothesis.

Scientists only change one factor or variable at a time. Otherwise they would not be able to work out which variable caused the effect. All the other variables must be kept exactly the same or constant. Joe then designed and ran two experiments that he thought could solve his problem:

Fig 1.7.1

•

Experiment 1: He put 3 drops of detergent in the sink each time. He ran hot water in very slowly at first, then repeated with hot but faster water. He repeated the experiment with very fast but equally hot water. Each time he filled the sink half-way.

•

Experiment 2: He put 1 drop of detergent in the sink and turned the tap on high until the sink was half full. He then repeated the experiment with 2 drops of detergent, then 3 then 4.

What affects froth production?

Be fair! Things happen due to lots of different factors. But which factor has the biggest effect and which ones don’t have any effect at all? Any test that a scientist carries out must be a fair one. To be fair, we need to

24

To make sure you design an effective experiment you should know: • the problem you are trying to solve (the aim) • exactly what you are going to measure • what you are going to change • what you are going to keep the same • anything else that might affect the experiment but you cannot control, Prac 2 p. 26 eg air pressure.

UNIT

1. 7

[ Questions ]

Checkpoint

UNIT

1.7 Skills 10 For both of Joe’s experiments: a State an aim. b List a detailed method using numbers to set the order. c Construct a results table. 11 Joe then wanted to test whether the temperature of the water had any effect on the froth. For this new experiment: a State Joe’s aim. b State a list of equipment he would need. c List a detailed method. d Construct a results table he could use.

1 State five points that you should know for an effective experiment. State an example of each point. 2 Explain what is meant by the term ‘variable’. 3 Explain why only one variable should be changed at a time.

Think 4 List some variables that may affect: a the number of visitors to a swimming pool b the growth of a plant c the time taken to cook a potato d the number of times you go to the toilet in a day e how long a detention a student receives f your test results for this topic

Analyse 5 List Joe’s four variables in the above experiment. 6 Identify the variable that Joe didn’t think was important. 7 List other variables that Joe didn’t identify. 8 Explain whether any of the variables that you listed in question 7 might be important to the experiment. 9 Describe a method that Joe could use to measure the froth of the detergent.

[ Extension ] Investigate 1 Nikki liked sweet coffee so she always added lots of sugar. She often noticed, however, that a lot of it remained undissolved at the bottom of the cup. a Describe three variables that you think would affect the amount of sugar dissolved in a cup of coffee. b List the variables in order from the most important to the least important. c Choose one important variable and describe a method to test it. 2 George heard an old tale that if you want an avocado to ripen quickly, you should place it in a brown paper bag with a banana! He thought this sounded weird and wanted to see if it was true. Describe in detail how he could test whether the tale was true or not. You may like to perform this experiment to see if your method works.

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scientifically Working Scientifically

UNIT

1. 7

[ Practical activities ] Froth production

Prac 1 Unit 1.7

Aim To interpret another student’s experiment and correctly write a report Equipment

PART 2 1 Test one of the variables that Joe did not test. 2 Once again, write up the experiment.

DYO

Questions

Dishwashing detergent with dropper, ruler, access to tap, large beaker/bucket/ice-cream container, thermometer

Method

1 State the variables that Joe tested. 2 Explain why Joe kept the variables the same in both experiments. 3 List three other variables that could have been tested.

PART 1 1 Repeat one of Joe’s experiments.

4 Describe which variable you think would have the most effect.

2 Write up the experiment, following the rules for writing a report.

Answering a question with an experiment Prac 2 Unit 1.7

During the Easter holidays, Clare noticed that when you drop a ball it never bounces back to the height you dropped it from. Why didn’t the ball come back as high?

Aim To identify variables and design a simple experiment

DYO

Equipment Tennis ball, metre ruler

Fig 1.7.2

Method 1 Identify all the variables that you think will have some effect on the bounce. 2 Decide which variable you are going to keep the same. 3 Describe, in as much detail as you can, an experiment that would test Clare’s sister’s statement. You will need to collect at least five different measurements. 4 Perform the experiment. 5 Construct a table for your results. 6 Make suggestions on how you could improve your experiments.

Questions 1 Identify which variables: a affected the bounce height b did not significantly affect the bounce height

Clare asked her sister about this and she replied, ‘The ball never gets back as high because it loses some energy. What’s more, once you get to a certain height of drop it never bounces any higher’. Clare decided to test her sister’s hypothesis.

26

2 State two conditions that would combine to produce: a a high bounce b a low bounce

UNIT

context

1. 8 One of the most important and dangerous pieces of equipment you will use in the laboratory is the Bunsen burner. Its correct use is essential for your safety.

This flame has a blue colour and is sometimes difficult to see, but can be heard. At the very base of the flame, there is a small cone of unburnt gas. The hottest part of the flame is just above this cone. The Bunsen burner flame

light blue dark blue

barrel

Prac 2 p. 30

Fig 1.8.2

hottest part of the flame cone of unburnt gas

gas hose

collar

air hole (gas jet inside)

Worksheet 1.5 The Bunsen burner Prac 3 p. 31

base

People in science Fig 1.8.1

A Bunsen burner

The collar controls the amount of air that enters the burner and controls the heat and colour of the flame. Prac 1 p. 29 It is very important that before lighting the Bunsen burner the collar is turned so that the air hole is shut. This causes very little air to mix with the gas, and so the gas does not burn well. It produces an easily visible, pale-yellow flame that is relatively cool. It is also a dirty flame because it leaves a layer of carbon on anything that is heated in it. This flame is called the safety flame because it is the coolest flame and is the easiest to see. If the collar is turned so that the air hole is open, a lot of air will enter. The gas will burn efficiently with no smoke and will be extremely hot (about 1500°C).

Robert Bunsen (1811–1899) Robert Bunsen, whose name we all associate with the Bunsen burner, was a German chemist in the 1800s. Bunsen invented many different pieces of laboratory apparatus, but the Bunsen burner was not one of them. It appears that Bunsen’s laboratory assistant, Peter Desdega, developed it, possibly from earlier designs by Michael Faraday. This presents a few questions: Who should get the credit? Who does the work in science? Bunsen worked on explosive arsenic compounds which almost killed him, and he lost one eye when a glass container exploded. Working with the German physicist Gustav Kirchhoff, Bunsen discovered two new elements—cesium and rubidium. A bachelor all his life, Bunsen developed a number of personality quirks, including not bathing!

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Using a Bunsen burner Other equipment often used with a Bunsen burner Prac 4 p. 32

Fig 1.8.3

evaporating dish

clay triangle Bunsen burner

tripod and gauze mat

retort stand, bosshead and clamp

bench mat

crucible and lid

UNIT

1. 8

[ Questions ]

Checkpoint 1 Sketch a labelled diagram of a Bunsen burner. 2 Describe how hot the blue Bunsen burner flame is. 3 Copy the following, and modify any incorrect statements so they become true: a The blue flame of a Bunsen burner is called the safety flame. b Yellow flames are ‘dirty’ flames. c The yellow flame is the hottest flame of the Bunsen burner. d The tip of the blue cone is the coolest part of the Bunsen burner flame. e There is no flame at the very top of the barrel. 4 Describe what you should do if: a you smell gas in the laboratory

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b a hissing sound is heard coming from a Bunsen burner that is not lit c you need to leave a Bunsen burner to collect some extra equipment

Think 5 Explain why the gas should be turned on after the match is lit. 6 Explain why you should not use a piece of burning paper to light a Bunsen burner. 7 Identify which flame is the hottest and how it is achieved. 8 Identify which flame is called the safety flame, giving reasons for your answer. 9 Explain the purpose of the airhole in a Bunsen burner.

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10 Explain why the rubber gas hose should be as flat as possible on the bench.

UNIT

1.8 [ Extension ]

11 Explain why the blue flame is noisier than the yellow. 12 Identify one thing that each of these students is doing wrong. Fig 1.8.4

Investigate 1 Research some of the achievements of Robert Bunsen. 2 Explain what natural gas is and where it comes from. 3 Identify the red material at the tip of a match and why it burns so easily.

Surf 4 Find out more about Bunsen burners by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 1, and clicking on the destinations button.

13 List five safety rules that you should follow when using a Bunsen burner for heating.

UNIT

1. 8

[ Practical activities ] Lighting a Bunsen burner

Prac 1 Unit 1.8

Aim To correctly and safely light a Bunsen

7 Carefully draw and colour a diagram of the yellow flame, looking carefully to see if there is any change in colour from the base of the flame to the top. Turn the collar so that the air hole is now half-open.

burner

8 Now open the air hole completely.

Equipment

9 Once again, carefully draw a coloured diagram of the blue flame and note any other features.

Bunsen burner, bench mat, matches, safety glasses

Method 1 Put on the safety glasses.

Questions

2 Place the burner on a bench mat.

1 State your observations about the flame when the air hole is half-open.

3 Connect the rubber tube to the gas jet on your bench, making sure the tube is reasonably flat on the bench.

2 Identify the colour of the flame when the air hole is open completely.

4 Turn the collar so that the air hole is closed.

3 Explain whether the air hole should be open or shut when lighting a Bunsen burner.

5 Light a match. Never use other materials, such as burning pieces of paper, to light a Bunsen burner. 6 Turn on the gas. At the same time, place the flame of the match just near the top of the burner. The burner should now light. If you lit it correctly, the flame should be yellow.

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Using a Bunsen burner

PART 2: Matches that won’t light!

Investigating the flame Prac 2 Unit 1.8

Method

Aim To investigate the flame of a Bunsen burner Equipment Bunsen burner, bench mat, matches and safety glasses, old and ‘bald’ gauze mat, pin, tongs, small piece of broken white porcelain

1 Set up the Bunsen burner. 2 Place a pin carefully straight through an unlit match, a little under its head. 3 Balance the pin on the top of the Bunsen burner so that the match head is in the centre of the barrel. 4 Light the burner as usual.

PART 1: Flame temperature

5 Quickly turn the collar so that you get a blue flame.

Method 1 Set up and light the Bunsen burner. 2 Set it to yellow. 3 With tongs, hold the gauze mat vertically in the flame so that it touches the top of the burner.

Holding the gauze mat

flame

inner cone of cold unburnt gas

Fig 1.8.5

pin safety match

Fig 1.8.6

The match head should be just above the top of the Bunsen burner

Questions 1 State whether your match lit up. 2 Predict the relative temperature of the flame at its centre. 3 Describe any observations you made about the pin, particularly at its edges. 4 Compare the heat at the centre with the heat at the edges of a Bunsen burner. 4 Now set the flame to blue and repeat the experiment. 5 Carefully draw diagrams of any heat markings that you see.

Questions

Method 1 Hold a small piece of porcelain in a pair of tongs.

1 If the wire glows red, state your inference about the flame at that point.

2 Hold the porcelain in a blue flame and record your observations.

2 Discuss whether the yellow flame is hot enough to make the gauze mat go red.

3 Hold the porcelain in the yellow flame and record what you see.

3 Describe the markings caused by the blue flame.

4 Copy the table on page 31 into your workbook and then complete it.

4 Sketch a diagram of a flame and label where the flame is hottest and where it is ‘coolest’.

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PART 3: Dirty and clean

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Air hole Noise of flame

Colour of flame

Coloured diagram of flame

Coloured diagram of gauze mat held in flame

UNIT

1.8 What happened to the porcelain held in the flame?

Closed Half-open Open

Questions 1 Describe what happened to the porcelain in the yellow flame and the blue flame.

How hot is hot? Prac 3 Unit 1.8

Aim To accurately measure an amount of water and heat using different flames Equipment Bunsen burner, bench mat, matches and safety glasses, tripod and gauze, 100 mL measuring cylinder, 250 mL beaker, stopwatch or clock with second markings

Method 1 Set up the equipment for boiling water as shown here.

2 State which flame could be called ‘dirty’. 3 Identify whether the ‘dirty’ flame was cool or hot.

2 Accurately measure 80 mL of tap water using the measuring cylinder and pour it into a 250 mL beaker. 3 Time how long it takes for the water to boil when using a blue Bunsen burner flame. Boiling will be obvious when the water begins to bubble vigorously. 4 Repeat the experiment with a yellow flame only.

Questions 1 Redraw the equipment in the correct scientific way. 2 State how long it took for the beaker of water to boil in each case. 3 Identify in which case the beaker boiled first. 4 Identify the flame colour that was the hottest. 5 Explain how you can tell which flame is the hottest.

bosshead

6 Explain how you can control the heat and colour of a Bunsen burner flame.

clamp thermometer

7 Explain why it is important to use the same quantity of water in each part of the experiment.

retort stand beaker gauze mat tripod Bunsen burner

box of matches

heat-proof mat

Fig 1.8.7

Equipment set up for heating water

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Using a Bunsen burner

How to heat a test tube Prac 4 Unit 1.8

Chapter review

Aim To safely heat a liquid in a test tube Equipment Bunsen burner, bench mat, matches and safety glasses, test tube, test tube rack, wooden tongs or peg

Method 1 Adjust a Bunsen to get a blue flame. 2 Fill the test tube to about 1/3 the way with water. 3 With tongs, hold the test tube near its top. 4 Point the test tube away from people, including yourself. 5 Heat the tube carefully near the bottom. 6 Move the tube in and out of the flame until the water starts to bubble. 7 Put the hot test tube in the test tube rack. 8 Record your observations.

[ Summary questions ] 1 Copy the following, and modify any incorrect statements so they become true: a Spatulas are used for stirring. b Goggles do not need to be worn when using chemicals. c Measuring cylinders are used to heat water in. d A gram is a unit used in the measurement of mass. e The air hole should always be shut when lighting a Bunsen burner. f The gas should always be turned on before the match is lit. g The air hole must be closed to produce the yellow flame. h Burning paper can be used to safely light a Bunsen burner. 2 Identify the branch or discipline of science in which these scientists would be working. a Amelia is calculating the fuel needed to launch a rocket. b Ying is looking down a microscope at a flu virus. c Olivia is watching ants at work. d Mike is developing a new plastic. 3 Scientists run experiments to obtain information. Apart from experiments, list other sources of information that scientists can use.

Fig 1.8.8

Heating a test tube – move the test tube in and out of the flame.

Questions 1 Explain why pointing test tubes at people is dangerous. 2 Outline why test tubes must always be kept moving in a flame. 3 Explain why tongs need to be kept near the top of the test tube and not the bottom. 4 Explain why test tubes should never be laid flat on a bench.

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4 State four observations about: a orange juice b an ice cube c the paper you write on in your workbook d dirt 5 Name a piece of equipment would you use to: a measure out roughly 100 mL of water b heat a small amount of liquid c heat strongly a small amount of solid d find the mass of a small stone e find the boiling point of water 6 List what you need to include in a good experimental report. 7 State the metric units you could use for measurements of: a mass (sometimes incorrectly called weight) b time c length or distance d temperature e speed f volume of a liquid

8 Identify which unit you would select to measure the following quantities. a the volume of water in Sydney Harbour b the mass of a car c the length of a rat d the mass of a dog e the volume of water in a bathtub

12 Compare the advantages and disadvantages of using a blue flame and a yellow flame on a Bunsen burner. 13 Draw and label the equipment that you would need: a to boil 200 mL of water b to boil 20 mL of water c to evaporate water from sea water

9 List the four most important steps in lighting a Bunsen burner, in the correct order.

[ Thinking questions ] 10 How observant are you? From memory: a Draw the shape of STOP and GIVE WAY traffic signs. b State the maximum speed shown on your parents’ car speedometer. c Identify whether your earlobes hang or are attached. d Identify whether the person sitting next to you is right- or left-handed. e State the number of pages in this textbook. 11 Collate the following into observations, inferences and predictions. a I’ve eaten something that was off. My stomach is not feeling well. I’ll vomit soon. b The plant required sun and water to grow. The plant will grow and fruit. The seed has a small leaf shoot breaking it in two.

14 Graeme noticed that his heart was beating fast after a cross-country run. He wanted to know what happened to his heartbeat before, during and after exercise. Design an experiment to find whether the number of heartbeats increases when you exercise and what it does if exercise stops.

[ Interpreting questions ] 15 In the case of the missing sausages, each observation was important in solving the case. The detective needed to infer something from each. Complete this list of observations in the case and state the logical inference that could be made from each:

Observation a

Vase was broken

b c

Window had been broken for a while Blond hair on carpet

d

Thief is hungry

e

Stone on the table

f

Next door’s lawn was mowed

g

Fritz was not hungry

h i

Inference

Someone entered via the window Curtains were all messed up

16 Describe each of the observations in question 15 as qualitative or quantitative. Worksheet 1.6 Being a scientist crossword Worksheet 1.7 Sci-words

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Solids, liquids and gases Key focus area:

4.2, 4.7.1, 4.7.2, 4.7.3

Outcomes

>>> The nature and practice of science By the end of this chapter you should be able to: explain the similarities and differences between solids, liquids and gases using observations and the particle theory use correct terms to describe what happens when a substance changes state, and explain how energy is involved use the particle model to explain dissolving, diffusion and expansion

Pre quiz

use densities to predict whether solids will float or sink, and how gases and liquids will arrange when mixed.

1 What’s the best way to get out of quicksand?

2 What causes the ‘fog’ on stage and in movies?

3 How can a steel ship float when a steel bolt sinks?

4 Why is gas, rather than liquid, used in shock absorbers?

5 Why does your breath produce ‘clouds’ on a cold day?

6 What is a model used for? 7 Does a scientific model always stay the same?

2

3.1 UNIT

UNIT

context

2.1 You get up in the morning and have a hot shower. Outside there is a mist in the air and frost has made the grass icy. Someone puts the kettle on and steam sprays upwards as it boils. Ice, water and steam are substances that we see and use almost every day.

Although they look and act completely differently from each other, they are just different forms of exactly the same thing—water—and contain exactly the same types of particles—water particles. Why then can you dive into a swimming pool but not into a big block of ice? Why is a steam burn more serious than one caused by boiling water? How can we explain this when we cannot see the individual particles of water? We use a model.

The particle model

Fig 2.1.1

Liquid water and solid ice are really the same substance.

Models in science We cannot see individual particles of water, but we do know how water (and ice and steam) behaves. In science, a model is an idea that explains certain behaviour. A model might not match exactly what is really going on, but it can be used to help us understand and predict what will happen in other situations, just like a model of a planned building or aircraft helps designers better understand the real thing. To better understand different forms of water and other substances, we use the particle model.

The word ‘substances’ is used a lot in science. It can be used to describe just about anything without being too specific. For example, if you don’t know what is made when two chemicals are mixed, you could answer ‘a substance’ and know you are correct! Instead of ‘substance’, we could try another word that can be used just as generally—matter. The annoying thing about substance and matter is their dictionary definitions. Look up ‘matter’, and you will very likely read that ‘matter is what all substances are made of’. Look up ‘substance’, and you get something like ‘anything made of matter’! One definition of matter is: ‘what everything in the universe is made of’. Another is: ‘anything that has mass and takes up space’. Now that the term ‘matter’ has been introduced, we can use it to say that there are three main states of matter—solids, liquids and gases. Ice, water and steam are all water, but in different states, or phases. There are other states as well that occur in special circumstances. The particle model of matter explains these states in terms of the packing and movement of the particles in a substance.

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The particle model

Viscosity and quicksand

solid

Fig 2.1.2

liquid

Particles in solids, liquids and gases vibrate, but those in liquids and gases are able to change position.

Solids In a solid, the particles are strongly bonded to each other. The particles in a solid move or vibrate, but not much when compared to liquids and gases. Solids have definite shape, do not flow, and are very difficult (virtually impossible) to compress. Solids do, however, have the potential to expand if heated but less than liquids and gases. The heat energy makes the particles Prac 1 p. 39 move or vibrate faster. Fig 2.1.3

gas

Viscosity describes how easily a liquid flows. Water, which flows easily, has a low viscosity, while honey, which does not flow as easily, has a high viscosity. Quicksand is an unusual substance because its viscosity increases when you try to move it quickly, making it harder to move through. If you are ever unfortunate enough to fall into quicksand, try floating and move very slowly to save yourself.

can flow to take the shape of the bottom of a container. Like solids, they are very difficult to compress—they are virtually incompressible. What do these have in common?

Prac 2 p. 40

Fig 2.1.4

What do these objects have in common?

Liquids The particles in a liquid are weakly bonded to each other, but it doesn’t take much to break these bonds (which is just as well when you jump into a swimming pool). The particles in a liquid move around more than those in a solid. Liquids have no definite shape, but

36

Fig 2.1.5

Liquids take the shape of their containers

UNIT

2.1 Brownian motion

Gases There are no bonds between the particles in a gas. The particles in a gas have much more energy than those of a solid or liquid, and fly around, bouncing off each other. Gases have no fixed shape. Even a small amount of gas will spread (or diffuse) to completely fill a container. Unlike solids and liquids, gases are compressible. This is because gases have large amounts of space in between the particles. It is this property that makes them useful in vehicle shock Prac 3 p. 40 absorbers.

When Robert Brown used a microscope to look at pollen grains suspended in water in 1827, he observed that the pollen grains were constantly moving around as if they were being jostled by something. The particle model explains this so-called Brownian motion as being caused by water particles, which vibrate and are able to move, bumping the pollen grains. Worksheet 2.1 The story of Robert Brown

pollen grain

Fig 2.1.7

Individual water molecules can’t be seen, but their effect on a pollen grain can be observed.

Dissolving

Diffusion may be demonstrated by removing a dividing plate between two gas jars, where one gas jar contains a different gas from the other.

Fig 2.1.6

As will be discussed in Chapter 3, dissolving can be explained in terms of particles of solute (e.g. sugar) spreading very thinly throughout particles of solvent (e.g. water). Dissolving can be explained using the particle model.

Fig 2.1.8

Evidence for the particle model In order for a scientific idea or model to be accepted, evidence is needed. This evidence needs to be based on good scientific research and experiments. After a scientist ‘discovers’ a new idea, they must work hard to collect all the evidence they can to prove their idea. This means that a scientist should be objective. To be objective means to rely on the evidence collected. A scientist must also repeat their experiments to show that it was not just luck that led to their discovery. When enough evidence has been collected the scientist must then prove to other scientists that what they have discovered is correct. The whole process can take years of work. The following is some of the objective evidence that was used to prove that the particle model is a good one.

solvent particles

solute particles

Smells Your nose is capable of detecting just a few particles of a substance when they dissolve in your nasal membranes. Car exhaust, cooking smells from a barbeque and perfume are small particles which spread by diffusion to our nasal membranes where

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The particle model nerve (to brain) particle dissolves in moist nasal membrane

Role play moist nasal membrane

A role play is another type of model that can help us explain something that is hard to see. In this role play you will experience the movement of particles. Organise a role play in which the class members act as particles which together represent a solid, then a liquid and finally a gas. After completing the role play write a description of the movement of the class members for each state of matter.

nose

nostril

Fig 2.1.9

It may need only one particle of a substance for a smell to be detected by the nose.

they are detected. Particles may also diffuse through solids and liquids; for example, an ink stain may spread through paper or clothes.

UNIT

2.1

11 Explain why an architect constructs a model of a building before it is built. Prac 4 p. 40

[ Questions ]

12 Identify a food or drink that contains: a both solid and liquid material b both a liquid and a gas c only solid d only liquid 13 Draw your own version of the particle model. Draw it as three layers, with solid at the bottom, changing into liquid and finally gas at the top.

Checkpoint Models in science

14 The particle model predicts that only gases can be compressed. Explain how.

1 Define the term ‘model’ as used in science.

The particle model 2 State your own definition of ‘matter’. 3 Describe what is meant by the term ‘phase of matter’.

Solids, liquids and gases 4 List five different examples each of a solid, a liquid and a gas. 5 Draw a diagram to compare the particles in solids, liquids and gases.

15 Describe what you think happens to the bonds (attractions) between particles as heat changes a material from solid to liquid to gas. 16 People might classify sugar and soft plasticine as liquids because they take the shape of their container. Clarify the definition of a solid so that people cannot make this mistake. 17 Explain how the fragrance of a perfume travels throughout a room.

Evidence for the particle model

18 Describe Brownian motion.

6 Define the term ‘objective’.

19 Copy and complete the following table to summarise the properties of substances.

7 Explain how Brownian Motion was first discovered.

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8 Describe what happens to the particles in a solid when it dissolves. Solid

Shape

definite

Think

Ease of compression

very low

10 Explain why, when trying to prove a new scientific model, a scientist should repeat their experiments a number of times.

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Property

9 Explain why diffusion is evidence for the particle model.

Bonds between particles Movement of particles

Liquid

weak medium

Gas

UNIT

2.1 Analyse 20 There must be some bonds or attractions, however weak, between the particles in a liquid. Explain why. 21 Explain why a liquid (brake fluid) is used in brake lines to transfer pressure to a car’s brakes from the foot pedal, while gas is used in shock absorbers. 22 Explain why foam rubber can be compressed, when solids are supposed to be incompressible.

23 Identify which of the following statements are objective (that is, they are based on evidence). a If I go outside with wet hair I will catch a cold. b I know it is raining outside because I can see the rain. c The X-rays showed that I have a broken arm. d Many people say that exercise is good for you.

[ Extension ] Create 1 Design a device that uses foam balls and an air blower with a variable speed control (say, a vacuum cleaner on reverse) to model the motion of particles in liquids and gases.

Investigate 2 Explain the difference between a fluid and a liquid. 3 Compare ‘true’ and amorphous solids, using examples of each. 4 Research the viscosity of liquids. Explain how temperature affects the viscosity of honey. 5 Explain what surface tension is and how it enables some insects to walk on water.

UNIT

2.1

6 Find out about capillary action and design an experiment to demonstrate it.

Surf Find out more about the following science applications by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools selecting chapter 2, and clicking on the destinations button. 7 Research solids, liquids and gases, and investigate ‘plasma’, the fourth state of matter. Compile a summary of the states of matter and their properties by using only labelled diagrams. 8 Oooze! Find out how to make a substance that acts like a liquid and a solid.

[ Practical activities ]

Fig 2.1.10

Plasticine particle models Prac 1 Unit 2.1

Aim To build a model showing the arrangement of particles in various solids

Equipment Plasticine

Method 1 Use the plasticine to make 16 identical balls. 2 Investigate the different ways you can pack several of the balls together in regular patterns. One way is shown opposite. 3 Sketch the different packing arrangements you come up with.

spheres arranged in a ‘body-centred cubic’ pattern

Questions 1 How many regular arrangements did you find? 2 State in which phase of matter you would most likely find regular packing patterns if you could see them.

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The particle model

Prac 2 Unit 2.1

‘Silly putty’ —solid or liquid?

3 Remove the lump of ‘silly putty’ and wash it under cold water.

Aim To determine whether ‘silly putty’ is a solid or a liquid

Questions

WARNING: Handle borax with care—use water to wash any spills. Check the relevant materials safety data sheet (MSDS).

Equipment Saturated borax solution, small container (e.g. film canister), white PVA glue, plastic spoon, small (100 mL) beaker

Method 1 Use the plastic spoon to measure out identical quantities (e.g. 2 spoonfuls each) of water and PVA glue into the 100 mL beaker. Mix thoroughly.

1 Roll your ‘silly putty’ into a ball. Describe how the ‘silly putty’ bounces. 2 Sit a ball of ‘silly putty’ on a flat bench top. Describe what it does over 5 minutes. 3 Put your ‘silly putty’ in a small container (e.g. a film canister). Describe how the silly putty changes shape over time. 4 Assess all your observations and decide which state of matter silly putty belongs in.

2 Use the plastic spoon again to measure out exactly the same amount (e.g. 2 spoonfuls) of borax solution. Add it to the water/glue mixture and stir rapidly.

Compressibility

Diffusion of food dye

Aim To compare the compressibility of a gas with that of a liquid

Equipment A plastic syringe (no needle attached), water, rubber stopper

Method 1 Draw some air into the syringe. 2 Press the opening of the syringe hard against the rubber stopper as shown, and try to compress the air by pushing the plunger.

syringe

2 Use particle diagrams to explain what happened with both substances.

Method 1 Almost fill a beaker or test tube with cold water. 2 Add a drop of food dye and let the mixture stand for several minutes, sketching what you observe every 30 seconds or so. 3 Repeat steps 1 and 2 using hot water. Fig 2.1.12

1 Explain why the spread of colour cannot be explained by gravity alone. 2 Explain how temperature affected your observations. 3 Explain the process of diffusion in this experiment in terms of particles.

one or two drops of food dye water

solid rubber stopper

40

Food dye, eye dropper, test tube or beaker

Questions Fig 2.1.11

Questions 1 State which substance you were able to compress.

Equipment

2

3 Now draw some water into the syringe and repeat step 2.

Aim To investigate diffusion in liquids Prac 4 Unit 2.1

1

Prac 3 Unit 2.1

test tube

UNIT

context

2.2 As discussed in Unit 2.1, substances can exist in three different states: solid, liquid and gas. Many of their uses rely on them changing from one state to another. Purifying water relies on a change of state from liquid to gas and back again, as does the formation

Applying a model

of rain. The burning of a candle relies on the wax changing from a solid to a liquid and then to a gas. Understanding how things change state is therefore very important.

Fig 2.2.1

Changing states of matter: solid state (ice), liquid state (water), gaseous state (steam)

In this unit we will use the particle model to help explain how substances change from one state to another—that is, from solid, to liquid, to gas and back again. Being able to use a model to explain how or why something happens is a very important skill. In each of the following sections, remember to keep thinking about what the particles are doing.

Solid to liquid To change a solid (e.g. ice) to a liquid (e.g. water), heat energy must be added to make the particles vibrate more. This causes solids to expand. Adding more heat energy eventually ‘loosens’ the bonds between the particles and a liquid is formed. This change is called melting. Another example is when a solid wax candle produces pools of liquid wax due to heat energy provided by the flame. The temperature at which a particular solid changes into a liquid is called the melting point. The melting point of water is 0°C, while the melting point of wax is around 60°C.

Liquid to solid The reverse of melting is solidification or freezing. When a liquid loses energy, the vibration of particles lessens and the bonds between particles are again strong enough to keep them in fixed positions. Liquid candle wax will naturally lose energy to the surrounding air and solidify when its temperature falls below about 60°C. Water will not freeze until it reaches 0°C.

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Changes of state

Liquid to gas To change a liquid into a Refrigerators gas, heat must be added to Refrigerators work by pumping a completely break the bonds liquid with a low boiling point, such as freon, through a between particles. When heat network of tubes in their walls, is added to a liquid, small close to food. The freon absorbs bubbles of gas will form heat energy from the food, lowering the temperature of the within the liquid. When food. The energy absorbed by enough heat is added, these the freon causes it to evaporate, gas bubbles become large but it is pumped to a condenser where it is converted back to enough to float to the surface liquid for another circuit. When and boiling occurs. When the freon is condensed, heat is a liquid boils, bubbles of also removed and is transferred to a grid of black wires at the gas escape into the air. rear of the refrigerator, where it This is called evaporation is allowed to dissipate into the or vaporisation. The room. Have you ever noticed the warm air at the rear of a fridge? temperature at which a liquid boils is called the boiling point. The boiling point of water is 100°C. A liquid does not have to boil in order for evaporation to occur—boiling just speeds up the process. A puddle of water will eventually evaporate on a dry day as Prac 1 particles at the surface absorb enough p. 45 energy from the air to escape the liquid.

Hot water freezing faster?

that a tub of People living in cold climates may tell you faster freeze will night cold a hot water left outside on A possible be? this can How . water cold of tub a than evaporation answer: because more water is lost due to , so a tub frozen be to water less is there tub, hot in the of cold tub a e befor freeze of hot water may actually . water. You might like to check this at home

Gas to liquid The opposite of evaporation is condensation. Condensation occurs when gas particles lose energy and turn into liquid. When you breathe out on a very cold day, the water vapour in your breath (which is a gas) condenses to form tiny droplets of water which are suspended in air and appear fog-like. A similar thing happens when you breathe on a window and water droplets condense on the glass.

larger bubbles

Boiling occurs when bubbles of gas escape from the liquid.

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Fig 2.2.2

DYO

Fig 2.2.3

Condensation

UNIT

2.2 Solid to gas A much less common change is when a solid absorbs heat and changes directly to a gas without melting and going through the liquid phase. This is called sublimation. An example of sublimation is when dry ice (frozen carbon dioxide) sublimes to form carbon dioxide gas. Dry ice is used on stage and in movies to produce the effect of fog. The word ‘sublimation’ may also be used to describe the action of a gas changing directly into a solid. Sublimation in action

Teacher demonstration Iodine sublimation CAUTION: Iodine gas is poisonous—exercise caution and use a fume cupboard. Check the MSDS. Safety glasses must be used. Seal the test tube with a rubber stopper after heating and leave inside the fume cupboard. Watch your teacher gently heat the test tube in a fume cupboard until a small amount of purple gas is produced. Observe what happens as the iodine cools.

Fig 2.2.4 Fig 2.2.6

test tube

speck of iodine fume cupboard Bunsen burner

heat-proof mat

Fig 2.2.5

Sublimation of iodine

Questions 1 Describe the iodine at the start of this demonstration and any changes in state that occurred 2 Identify whether any liquid iodine formed. 3 Describe the coating on the side of the test tube as the contents cooled. 4 Explain how you know that the purple substance produced after heating was a gas.

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Changes of state Summary Figure 2.2.7 summarises the different changes of state. Worksheet 2.2 States of matter

solid

Think 11 State the scientific term used to describe when: a a liquid changes into a gas b a gas changes into a liquid c a solid changes directly into a gas

evaporation (vaporisation)

liquid

solidification (freezing)

gas

condensation

lose heat sublimation

Fig 2.2.7

9 Explain why it is unusual to find substances that undergo sublimation. 10 Identify two substances that sublime.

gain heat

melting

Solid to gas

Changes of state

12 Identify which of the following is likely to be closest to the melting point of steel. A 0°C B 60°C C 100°C D 1500°C 13 Identify which of the following is likely to be closest to the melting point of oxygen. A 200°C B 0°C C 20°C D 100°C 14 Explain what would happen to an unlit wax candle on a 40°C day. 15 State another term for ‘evaporation’.

UNIT

2.2

[ Questions ]

Checkpoint Solid to liquid 1 Identify which change of state the term ‘melting’ refers to. 2 Describe what is meant by ‘melting point’. 3 Describe what happens at the melting point of water and identify at what temperature it happens.

Liquid to solid 4 Identify the two names given to a change of state from liquid to solid. 5 Identify the freezing point of wax.

Liquid to gas 6 Define the terms ‘boiling’ and ‘evaporation’. 7 Describe what happens to the particles when water boils.

Gas to liquid 8 Explain what is occurring in Figure 2.2.3.

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16 State the opposite term to: a melting b condensation 17 Describe three changes of state that may occur in the home. 18 Explain how heat is transferred when a solid sublimes. 19 List the advantages of dry ice compared with water ice when producing fog for a stage effect.

Analyse 20 Draw a change of state diagram based on a triangle with solid, liquid and gas at the corners. On each side of the triangle, indicate the name of the process of the change in state, in each direction (e.g. melting). 21 Kevin notices that when his pool is heated to 27°C, the water level falls by about 10 cm each week. a Explain how this can happen when 27°C is a lot lower than the boiling point of water, 100°C. b Predict what would happen if the pool was: i not heated ii heated to a higher temperature, say 30°C

UNIT

2.2 [ Extension ] Investigate

Surf

1 Prepare a list of melting points and boiling points for several substances.

4 Find out more about dry ice and sublimation by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools selecting chapter 2, and clicking on the destinations button. Produce a brochure with a set of rules for handling dry ice safely.

2 Investigate the history of the thermometer, and the three different temperature scales (Celsius, Fahrenheit, Kelvin). 3 Describe ‘snap freezing’ and ‘freeze-drying’.

UNIT

2.2

[ Practical activity] Ice to water to steam temperature graph Fig 2.2.8

Aim To investigate what happens Prac 1 Unit 2.2

to the temperature of water as it changes state

Equipment

thermometer

Ice cubes, heat-proof mat, water, gauze mat, beaker (250 mL), measuring cylinder (100 mL), thermometer (0°C to 110°C) or temperature probe, Bunsen burner, tripod

Method 1 Mix several ice cubes with 100 mL of water. 2 Place the thermometer in the ice/water mixture and record the temperature once every minute for 3 minutes.

ice + water gauze mat

3 Light the Bunsen burner and keep the air hole opening in the same position throughout the experiment. 4 Heat the ice/water mixture, and continue to record the temperature at 1-minute intervals until the water boils. Measure the temperature for 3 more minutes after boiling starts, but stop boiling if the water level falls below 50 mL.

tripod Bunsen burner

heat-proof mat

5 Record your measurements in a table.

Questions 1 Present the results in a graph showing temperature on the vertical axis and time in minutes on the horizontal axis. 2 Explain why you had to keep the air hole opening fixed during the experiment. 3 Explain why your graph did not quite start at 0°C.

4 Identify any level sections in your graph. Explain why level sections may occur. 5 Imagine you were able to capture the steam produced when all the water has evaporated and measure its temperature as you continued to heat it. Describe the temperature graph that would be observed.

45

Science focus: Observation and discovery Prescribed focus area: The nature and practice of science When we study matter, the particles are so small that we cannot see the individual particles. It is through observation and experiment that we have been able to reach our present understanding of matter. Although we cannot see the particles, there has always been evidence available for those who are observant enough to notice it, and interested enough to try and understand what they see. One of the most useful techniques that scientists use to help them understand things that are difficult to observe directly is to create a model. A model is based on information collected gained from observation and experiments. A model is a way of showing or explaining what we observe and measure in science. It allows us to show our findings in a way that others can understand. A model might not match exactly what is really going on, but it is useful if it helps us predict and understand what will happen in a certain situation. By early in the nineteenth century, experiments on the behaviour of different states of matter had led to the kinetic theory of matter. Part of this theory stated that all the tiny particles of matter constantly move, which we now know to be true. The model of tiny particles of matter that developed was all based on deduction, (making conclusions based on evidence) rather than on direct observation of the particles themselves.

Fig SF2.1

Models for the three states of matter. This model predicts the behaviour of the particles in solids, liquids and gases.

Solid

46

Liquid

These models of a new space plane being built in Japan will be tested in a wind tunnel. Scientists will use the information collected from the models to predict and explain what will happen when they make a real space plane.

Fig SF2.2

Gas

A scientist is an observant person who notices things happening and then wonders why they occur. Having made observations, a good scientist will then investigate further, to try and understand what they have observed. One creative and enthusiastic scientist’s search for understanding led to the first observation of molecules in motion. The British botanist Robert Brown led a very

The British botanist Robert Brown was interested in understanding the world around him.

Knowing that the tiny pollen grains were not alive, Brown wondered why they appeared to be moving about. He decided to investigate further and placed a tiny drop of a stain, made from ground dried petals, into a drop of water on a microscope slide. He was surprised to see that the tiny particles of the stain also jiggled about and moved in the drop of water. Brown was unable to provide a full explanation for his observations, but he reported his findings anyway. The motion of tiny non-living objects jiggling about and moving through a drop of water, when viewed with a microscope, became known as Brownian motion.

Fig SF2.3

interesting life. After meeting Joseph Banks, he sailed with Matthew Flinders to Australia and collected vast numbers of specimens of Australian plants. When he returned to England, his studies provided important information about the different types of plants that are found. Brown used a microscope to study plants and was the first to observe and name the large structure found in all living cells, the nucleus. It was while using his microscope to make observations on tiny pollen grains from one of his plant specimens that he made an interesting observation. As he looked through the microscope, the pollen grains sat on the microscope slide in a drop of water. The pollen grains were not alive, yet Brown could see them jiggling and slowly moving about in zigzag paths through the water.

Jiggling pollen grains in a drop of water. In the diagram the blue lines represent the movement of the blue water molecules, while the wiggly red lines show the movement of the pollen grains. Pollen grains

[ Student activities ] 1 a Describe what a model is. b Describe an example of how the particle model can be used to predict the behaviour of each state of matter when a solid is heated. c Investigate and explain what these other scientific terms mean, and when they are used: inference, hypothesis, prediction, theory, law, observation. 2 a Outline the features of a good scientific model that can lead to it becoming accepted without anybody seeing the thing that the model suggests is there. b Discuss this in a group and create a final list of the most important features of a good scientific model. c Present your findings to the class. 3 The inference from ‘Brownian motion’ is that the water molecules moving in the water droplet, although too small to see, are observed because of the jiggling effect

Fig SF2.4

Drop of water on microscope slide

produced by their collisions with the pollen grains. Create a short story, or comic strip, to show how the water molecules bumping into the pollen grains produce ‘Brownian motion’. 4 Brown mounted the pollen grains in water at room temperature. Another experiment that would have been useful would be to place identical pollen grains into a drop of warm water. a Explain why this experiment might have assisted Brown in understanding what he saw. b Predict the result you would expect to observe. c Use a microscope to test your prediction. 5 a Describe the features of Robert Brown’s approach that enabled him to make an important contribution to science knowledge. b Outline how technology might have helped Brown in his work.

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UNIT

>>>

context

2.3 Have you noticed that your watch is tighter on your arm in summer than in winter? This is because the liquid in our body expands as the temperature rises and so our arm gets a little thicker. Solids, liquids and gases all expand (get bigger) when heated. Expansion can be useful and can be used to activate devices such as a fire alarm. It can also cause problems like making train tracks buckle in the heat.

Expansion and particles Solids, liquids and gases do not always change state if they gain or lose heat energy. Whether or not a change of state occurs depends on how much heat is gained or lost. Even if no change of state occurs, a material is still affected—it will expand or contract (get smaller). The particle model can explain expansion and contraction. When a solid or liquid is heated, its particles vibrate more rapidly and push each other further apart, so the substance takes up more space, or has expanded. In a gas, particles move with higher speed and push harder against anything they come in contact with. If the gas were in a balloon, the balloon would expand. If the gas were heated in a steel cylinder, it would be unable to expand, but the pressure it exerted on the walls of the cylinder would increase (due to more energetic particles).

Expansion of solids Different solids expand at different rates. The table above shows how much a 1-metre length of particular solids will expand when the temperature is increased by 1, 10 and 100°C. Notice that steel and concrete expand at the same rate. This allows steel to be used as reinforcement for concrete without the risk of cracking caused by one material expanding at a different rate to the other. Consider what would happen if aluminium bars were used instead of steel.

48

1-metre length expansion table Temperature rise

1°C

Solid

10°C

100°C

Expansion amount in millimetres

Invar (nickel/steel mixture)

0.001

0.01

0.1

Wood (oak)

0.003

0.03

0.3

Pyrex

0.003

0.03

0.3

Glass

0.009

0.09

0.9

Platinum

0.009

0.09

0.9

Steel

0.011

0.11

1.1

Concrete

0.011

0.11

1.1

Iron

0.012

0.12

1.2

Brass

0.019

0.19

1.9

Aluminium

0.025

0.25

2.5

concrete slab

steel reinforcing rod

Fig 2.3.1

Reinforced concrete has steel rods to allow it to contract and expand without cracking and to give it more strength.

The steel rods may be heated before the concrete sets, so that after the concrete has hardened, the rods try to contract and this pulls the concrete more tightly together. This is called pre-stressing. Expansion gaps must be left in bridges and railway tracks, otherwise they may buckle as they expand in warm weather. You may also have noticed that power lines sag more on hot days due to expansion.

expansion gap

expansion gap

UNIT

2.3 invar brass invar heat

brass

Expansion gap in a bridge

Fig 2.3.2

Fig 2.3.5

Brass expands more than invar when heated, so how many ways could this bimetallic strip bend?

+ –

battery

cold day

alarm bell

bimetallic strip bends upwards to complete the circuit and turn on the alarm bell

hot day

Why are power lines strung with some sagging?

Prac 1 p. 53

Fig 2.3.4 Fig 2.3.6

Prac 2 p. 53

Fig 2.3.7

By applying the expansion theory we can loosen tight-fitting jar lids. Look at the expansion differences between glass and steel in the expansion table. Notice that steel will expand more than glass when we raise the temperature by 100°C. The ends of a garden hose may be heated by placing them in hot water so they expand and are more easily joined. When the hose ends cool down, they contract and fit together more tightly.

Cracking dishes A cold dish or glass may crack when it’s run under hot water, due to one side expanding faster than the other, forcing the object to crack. Not all expansion is a nuisance. A thermostat in a heater, oven or refrigerator may contain a bimetallic strip that controls a switch. As the name suggests, a bimetallic strip is made of two different metals. The strip bends when heated, because one metal expands a greater distance than the other, just as a runner on the outside of a curved track runs further than a runner in an inside lane.

A bimetallic strip used in a fire alarm Expansion and contraction can be useful when joining two plastic garden hoses.

Prac 3 p. 53

joiner

expanded hose (heated in warm water)

after cooling

Expansion of liquids In general, liquids expand much more than solids when heated. Care must be taken to leave space for liquids to expand into when filling containers such as

49

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Expansion petrol and liquid petroleum gas (LPG) tanks. A car radiator contains water that is used to cool the engine. This water expands when it absorbs engine heat, and may overflow into an expansion chamber. Any further expansion of water in the radiator will cause an overflow into the expansion chamber.

Fig 2.3.8

If water at 4°C didn’t sink to the bottom of lakes and ponds when they freeze in winter, fish and other animals wouldn’t be able to survive. By sinking below the ice layer, water at 4°C is insulated from the surroundings by the ice layer and will not freeze as easily. It’s just as well water behaves strangely compared to other liquids! Fish in ponds prone to freezing survive because ponds freeze from the top down, not the bottom up.

expansion chamber

Fig 2.3.10

radiator

ice layer

Thermometers are used to measure temperature. They contain a liquid—mercury or coloured alcohol— in a bulb connected to a narrow tube that makes the liquid rise noticeably when heated. Clinical thermometers containing mercury have a kink with a constriction (narrowing) at the lower end to prevent the mercury falling back after a patient’s temperature has been taken, allowing more time to read the temperature accurately. Fig 2.3.9

A clinical thermometer

42 41 40 39

constriction 38 37 36 35

mercury in bulb

1°C 2°C 3°C 4°C

Expansion of gases Gases react to changes in temperature more than solids and liquids do. A gas will try to expand if heated, but may be prevented from doing so by its container. Since the particles of a gas will diffuse to completely fill a container, it’s not always quite correct to say that gases contract to take up less space. Instead we say that a gas exerts less pressure when it is cooled or more pressure when it is heated in a container. The expansion of gas may be demonstrated as shown here. The gas (air) in the test tube expands due to heat from the hand and is forced into the beaker.

The unusual behaviour of water Water at 4°C or above will expand like other substances if heated, and water (or ice) at 0°C will contract like other substances if cooled, but between 0°C and 4°C, water behaves quite strangely! As the temperature of water changes from 0°C to 4°C, instead of expanding, the water contracts! When a substance contracts, its particles become more closely or densely packed together (we say the density of the substance has increased). So, water is densest at 4°C and will sink through liquid layers at other temperatures.

50

Fig 2.3.11

UNIT

2.3 Hot air balloons rise to great heights by making use of the fact that hot, expanded gas is less dense than cooler gas. Worksheet 2.3 Expansion graphs

UNIT

2.3

[ Questions ]

Checkpoint Expansion and particles 1 Copy and complete: Substances generally ______ when heated and ______ when cooled. 2 Explain what the particles in a substance do when heated to take up more space.

Expansion of solids 3 Describe what happens to the movement of the particles in a solid as it is heated.

Fig 2.3.12

4 Figure 2.3.13 shows a solid in terms of the particle model. Identify whether Figure 2.3.14, 2.3.15 or 2.3.16 best shows the solid after heating. Fig. 2.3.13

Hot, expanded, low–density air makes this balloon rise.

Before heating

Fig 2.3.14

Expansion of liquids 5 State whether liquids expand more or less than solids when heated. Give a reason for your answer. 6 Describe two uses of expanding liquids.

Expansion of gases 7 Identify what may be used to prevent a gas expanding when heated. 8 State what happens to the pressure as gas is heated inside a container.

Think 9 a Identify two problems that expanding solids can cause. b Explain how each problem is overcome.

Fig 2.3.15

Fig 2.3.16

10 Use the expansion table on page 50 to identify which solid or solids expand: a most when heated d the same as platinum b least when heated e three times more than wood c the same as steel f four times more than pyrex 11 Copy and complete: A gas trapped in a container that is heated will exert more _____ on the walls than in a cold container. 12 State why you think mercury or coloured alcohol is used in thermometers instead of coloured water. 13 Explain why it is more important to have a constriction in a clinical thermometer than in a laboratory one. 14 Describe why a clinical thermometer is usually shaken after use.

>> 51

Expansion

15 Identify the temperatures at which water does the opposite of what other substances do. 16 Describe how the fish in a lake can survive when the lake freezes. 17 Explain why there are ‘lines’ in a concrete footpath. 18 Some barbecue hotplates make sounds when they are first heated or begin to cool down. Describe what causes these sounds.

Analyse 19 Explain what the particles in a gas are doing to cause pressure.

>>> [ Extension ] Investigate 1 Research how a spiral of bimetallic strip can be used as a temperature gauge or how it is used in flashing car indicators. 2 Investigate the expansion of air using an apparatus similar to the one shown in Figure 2.3.17. Fig 2.3.17

20 A light globe is made of glass with a platinum filament. a Use the table on page 48 to state the expansion abilities of both glass and platinum. b Describe what you notice about their expansion abilities. c Explain why the answer to part b is important. 21 Explain why invar is often used to make accurate technical instruments that are used in hot situations.

small balloon

string

weight

22 Identify which type of bimetallic strip would bend most when heated—one made of iron and brass, or one made of iron and aluminium. 23 Draw a diagram to demonstrate how a bimetallic strip can be used in a switch. 24 Identify how much the following materials would expand by. a a 1 metre steel rod heated so that its temperature rises by 100°C b a 1 m plank of wood that increases in temperature by 1°C c a 2 m block of concrete heated so that its temperature goes up by 10°C d a 50 cm iron rod that increases in temperature by 100°C 25 List the following in order from least to greatest expansion when heated: concrete, pyrex, brass, platinum.

Skills 26 Draw a bar graph comparing the expansion of different substances using the information in the table on page 48. 27 Construct a table like the one on page 48, but for a 10-metre length of each material.

52

Surf Find out how different types of thermometers work by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 2, and clicking on the destinations button.

UNIT

2.3

[ Practical activities ]

UNIT

2.3 Fig 2.3.18

Ball and hoop Prac 1 Unit 2.3

Aim To investigate the expansion of metals on heating Equipment Ball and hoop apparatus, tongs, Bunsen burner, heat-proof mat

Method 1 Check that the ball fits through the hoop when both are at room temperature.

An expansion gauge Prac 2 Unit 2.3

Aim To construct an apparatus to compare the expansion of different metals Equipment Metal rod, clamps, pivot, ruler, Bunsen burner, splint, heat-proof mat

Method

3 Use the tongs to carefully place the ball on the hoop. Does it still fit through? 4 Place the equipment onto the heat-proof mat to cool. The brass ball will remain hot for a long time. BE VERY CAREFUL.

1 Assemble the apparatus as shown.

Questions

metal rod

1 Identify the scientific idea or concept that this activity demonstrates.

clamp

retort stand

2 Heat the ball over a Bunsen burner (blue flame) for a minute or so. DO NOT HEAT THE CHAIN.

2 A different the ball did not fit through the hoop at room temperature. Explain what you would do to make it fit.

Bunsen burner

The bimetallic strip

ruler splint Prac 3 Unit 2.3

pivot

Fig 2.3.19 2 Use a Bunsen burner to apply heat to the metal rod.

Aim To investigate the operation of a bimetallic strip Equipment Bimetallic strip, tongs, Bunsen burner, heat-proof mat

Method 1 Hold a bimetallic strip using the tongs and heat it in a Bunsen burner flame until you notice an effect.

3 Repeat using a rod made from a different metal.

2 Repeat the experiment but this time heat the other side of the bimetallic strip.

Questions

Questions

1 Explain why a long splint is better than a short one.

1 Describe what would happen as more heat is applied.

2 Describe what you should do to ensure a fair comparison of different metals using this apparatus.

2 Explain how you can tell which side of the strip is expanding the most.

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UNIT

context

2.4 Which weighs more—a kilogram of lead or a kilogram of feathers? The answer to this old trick question is, of course, that they both weigh the same—1 kilogram! What people may be thinking of when they wrongly answer ‘a kilogram of lead’ is the different density of each substance. The density of substances determines whether they float or sink. If a substance floats on water, then it is less dense than the water it floats on.

Introducing density We used the term ‘density’ in the last section to describe how closely the particles in a substance are packed together; for example, hot air is less dense than cold air because the particles are more spread out. We can extend this idea to compare the densities of different substances by considering how much mass is packed into each cubic centimetre. A technical definition of density is: ‘the mass of a 1-centimetre cube of a substance’. The densities of several substances are shown in Figure 2.4.1.

Each of these cubes has a volume of 1 cubic centimetre (1 cm3)

Fig 2.4.1

Black holes

54

air

foam rubber

wood

oil

water

glass

steel

iron

copper

lead

gold

Astronomers believe that black holes in outer space come in various sizes, some no bigger than a pinhead, but with a mass many times greater than that of our sun, making black holes the densest objects imaginable! The gravitational attraction of black holes is so strong that not even light can escape.

Calculating density Of course, most substances are not easily available in the form of 1-centimetre cubes, so how can we find their densities? To calculate the density of a substance, we need to know two things about a sample of the substance: its mass (e.g. in grams) and its volume (e.g. in cubic centimetres, or cm3 for short). The volume, or space taken up by an object, can be found in one of two ways.

Volume If the object is a rectangular prism, its volume is found by multiplying length x width x height (you may recall the formula V = L x W x H from maths).

H = 2 cm

Volume V =LxWxH =4x3x2 = 24 cm3

W = 3 cm L = 4 cm

If an object is irregular, or ‘odd shaped’, its volume may be found by measuring the rise in water level when it is placed into a measuring cylinder containing enough water to cover the object. Note that 1 mL takes up the same space as 1 cubic centimetre. This method will not work, however, if the object is porous or absorbs any water.

Calculation example Consider a lump of plasticine having a mass of 4.8 grams and a volume of 3 cubic centimetres. To find the density we can use the rule: density = mass ÷ volume So for our lump of plasticine, density = 4.8 ÷ 3 = 1.6 grams per cubic centimetre or 1.6 g/cm3 for short. Another way of writing the rule for density is: density = mass volume or D = m V/ Prac 1 Prac 2 p. 58

Fig 2.4.2

UNIT

2. 4

p. 59

Prac 3 p. 59

Worksheet 2.4 Density calculations

Floating and sinking 110

110

100

100

90

90

80

75 mL

80

70

70

60

60

50

50 mL

An object will float if its density (or average density) is less than that of the liquid it is in. Pure water has a density of 1 g/cm3. This means that for objects placed in water, their density must be less than 1 if they are to float.

50

40

40

30

30

20

20

10

10

lower density than the liquid

same density as liquid

greater density than liquid

Fig 2.4.3

The object in the measuring cylinder at right has a volume of 75 – 50 = 25 mL or 25 cubic centimetres.

Whether or not an object will float depends on how its density compares with the density of the liquid it is in.

Fig 2.4.4

55

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Density Ice is less dense than water, so it will float. Steel is more dense than water, so it will sink in water. Salt water is more dense than fresh water, making it easier to float in the ocean than in a freshwater lake or river. An egg will sink in fresh water, because its average density is just greater than that of the water. Mixing some salt in the water increases the density of the liquid to just greater than that of the egg. The egg’s density is now less than the liquid’s, and the egg floats. Confirm this fact by repeating the experiment at home.

Fish contain a swim bladder that can be used to control the fish’s average density by adding or removing air. This allows the fish to float, sink or stay suspended as it swims. Changes to the temperature or the amount of salt in the water can affect its density, so a fish may need to be able to alter its density just to remain at the same depth. Scuba divers wear inflatable vests that use the compressed air from their tanks to do the same job. Submarines work on the same principle, using compressed air to expel water from ballast tanks, getting lighter in the process.

Fig 2.4.5 hydrometer

Brewing scientifically fresh water

egg

Density of egg is greater than density of liquid

UNIT

2.4

salt water

Density of egg is less than density of liquid

[ Questions ]

weaker beer

Checkpoint Introducing density 1 State which weighs more: a tonne of gold or a tonne of sawdust. 2 Describe what is meant by the density of a substance. 3 State the density of: a water c copper b wood d gold

Calculating density 4 Identify two things we need to know to find the density of an object. 5 State the formula for: a the volume of a prism b density 6 Describe two ways to find the volume of an object.

56

stronger beer

Beer brewers use a hydrometer to measure the density of beer at various stages in the brewing process. Depending on the alcoholic strength of the liquid, the hydrometer floats at different levels. A higher alcohol content causes the brew to have a higher density. The higher the density of a liquid, the higher an object will float.

Fig 2.4.6

Brewers use the term ‘specific gravity’ to refer to density.

Floating and sinking 7 Describe how you could predict whether an object will float or sink in a liquid. 8 Explain why an egg will float in salt water, but not in fresh water. 9 Describe a swim bladder and how it is used. 10 Explain how steel-hulled ships can float when steel is more dense than water.

UNIT

2. 4 16 Calculate the density of each of the following:

Skills 11 A piece of metal has a mass of 6 grams and a volume of 2 cubic centimetres. Calculate the density of the metal. 12 Calculate the volume of a block of glass of length 4 cm, width 2 cm and height 3 cm.

32 g

2 cm

13 Calculate the volume of the brick in Figure 2.4.7.

26.4 g 4 cm

2 cm 4 cm

3 cm

2 cm

Fig 2.4.9

Fig 2.4.10

6 cm 90 g 8 cm

Fig 2.4.7

volume = 50 cm3

Fig 2.4.11 14 Calculate the volume of the stone shown in Figure 2.4.8. Fig 2.4.8

5 cm

7700 kg

20 cm

5 cm

4 cm

Fig 2.4.12

17 Calculate the density of a type of rubber if a sample of it has mass 75 g and volume 50 cm3. 18 Calculate the volume of the object in the measuring cylinder in Figure 2.4.13 if it contains 30 mL of liquid. 19 A type of garden potting mix has a density of 1.2 g/cm3. Calculate the mass of 2 litres (2000 cm3) of this potting mix. 20 Calculate the mass of 4 cubic centimetres of gold. Fig 2.4.13

>> 15 If the mass of the stone in question 14 is 32 grams, calculate its density.

>> 57

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Density

21 The tile shown in Figure 2.4.14 has a density of 2.5 g/cm3. Calculate how much a load of 100 of these tiles would weigh. Fig 2.4.14

4 cm

10 cm

23 A lump of brand A concrete has the same mass as a lump of brand B concrete, but the brand B lump has less volume. State which concrete brand is the most dense. 24 Describe how you could find the density of an oil sample using a beaker, an electronic balance and a calculator. 25 Oil floats on water. Compare the density of oil to the density of water. 26 Perspex has the same density as a type of cooking oil, but a lower density than water. Draw a diagram to demonstrate what would happen if all three are placed in the one beaker.

[ Extension ]

10 cm

Investigate Think

1 Research what Plimsoll lines on ships are used for.

22 Two blocks of wood, one oak and the other cedar, have the same volume, but the cedar block has less mass than the oak. Compare the densities of oak and cedar.

UNIT

2. 4

[ Practical activities ] Density of cubes

Prac 1 Unit 2.4

2 Explain how Archimedes helped the King of Syracuse to determine whether the goldsmith who made the king’s crown used pure gold or not.

Aim To measure and calculate the density of cubes of different substances

3 Copy and complete the table below for each 2 cm cube.

Equipment

Substance

Density kit containing 1-centimetre and 2-centimetre cubes of various substances, scales, ruler, calculator

Aluminium

8

Brass

8

Method

Mass (g)

Volume (cm3)

Density (g/cm3)

8

1 Find the mass of each cube using the scales. 2 Copy and complete the table below for each 1 cm cube.

Substance

Mass (g)

Volume (cm3)

Aluminium

1

Brass

1 1

58

Density (g/cm3)

Questions 1 Explain why 8 is given as the volume of the larger cubes when the side length of each cube is only 2 cm. 2 Identify which of the densities you calculated were similar. Explain this result. 3 List the substances in order of density from smallest to largest.

Density of irregular objects Prac 2 Unit 2.4

Aim To determine the density of various objects by displacing water

Equipment Measuring cylinder (100 mL), various irregular objects small enough to fit in the measuring cylinder, e.g. stone, ball bearing, bolt, plasticine, scales, water

Method

Density of liquids Aim To design an experiment to determine the Prac 3 Unit 2.4

density of various common liquids

Equipment

Measuring cylinder, scales, various liquids (e.g. water, cooking oil, kerosene, salt water, turpentine)

Method 1 Devise a way of finding the mass of, say, 50 mL of each liquid.

1 Find the mass of each object using the scales.

2 Calculate the density of each liquid.

2 Place 50 mL of water in the measuring cylinder.

Questions

3 Hold the measuring cylinder at an angle and gently slide one of the objects into the water. Note the new water level and hence find the volume of the object. 4 Repeat steps 2 and 3 for the other objects. 5 Copy and complete the table shown.

Object

Mass (g)

Volume (cm3)

UNIT

2. 4

1 Explain how you found the mass of the liquid in each case. 2 Draw a diagram to demonstrate where each liquid would float if all the liquids were all placed in the one beaker and allowed to settle into layers. Hint: the most dense layer will be at the bottom.

Density (g/cm3)

Questions 1 Compare your densities with those found from previous experiments or from Figure 2.4.1. 2 List the possible sources of error in this experiment.

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>>> Chapter review c An object will float if it has a higher density than the liquid it is in.

[ Summary questions ] 1 State the three phases of matter. 2 Describe a household example of each of the states of matter. 3 Copy and complete: Matter is something that takes up _____ and has _____. 4 Complete the table below, summarising the different possible changes of state.

To

From

Solid

Solid

Liquid

Gas

melting

Liquid Gas

5 Identify all the changes of state involved when a container of frozen soup is thawed out and boiled. 6 Identify a substance that sublimes. 7 State the opposite term to ‘expansion’.

19 Describe a method you could use to find the volume of a brussels sprout. 20 Calculate the volume of the block of metal shown.

1100 kg

21 Calculate the density of the block of metal shown.

4 cm

5 cm

5 cm

[ Interpreting questions ]

10 Identify two phenomena in this chapter that can be explained by the particle model.

22 Identify at which of the following temperatures water is the most dense. Give a reason for your answer. A 0°C B 1°C C 3°C D 5°C

[ Thinking questions ]

23 Draw a diagram to demonstrate how a bimetallic strip may be used to control the heating element in an electric iron.

8 Copy and complete: Expansion is more noticeable at __________ temperatures or in __________ objects. 9 Explain what a model is and why they are used in science.

11 Identify three other models that are used in science to help us better understand a phenomenon. 12 Compare the bonds between particles in a solid with those in a liquid.

24 Explain how a thermometer works. 26 Sometimes when oil spills from a ship at sea it catches alight. Explain why this is possible given that there is so much water.

13 List which states of matter are compressible.

27 Explain what causes gas to exert pressure when placed in a container.

14 Describe one piece of evidence that supports the particle model.

28 Design an experiment to find the density of a piece of metal that has an irregular shape.

15 Explain why a dish may crack when run under hot water.

29 Using your knowledge of the particle model, draw diagrams to demonstrate the arrangement and motion of particles in a solid, a liquid and a gas.

16 Substance A has a melting point of 10°C. Identify its state at normal room temperature. 17 True or false? a Density is how heavy an object is. b Density describes the amount of mass in a certain volume.

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18 Identify which of the following are possible units for density. (There may be more than one answer.) A grams B cubic centimetres C cubic centimetres per gram D grams per cubic centimetre E kilograms per cubic metre

Worksheet 2.5 Solids, liquids and gases crossword Worksheet 2.6 Sci-words

>>>

3

Mixtures and their separation

Key focus area:

>>> The applications and uses of science

describe the importance and properties of mixtures that contain water describe and use simple techniques to separate mixtures into their parts.

and water are mixed?

3 Is sea water a pure substance or a mixture of substances?

4 How does a washing machine remove most of the water from washed clothes?

5 How would you separate a mixture of sand and salt?

6 When you push the button on the toilet, where does all the stuff go?

Pre quiz

1 What is a mixture? 2 What happens when oil

Outcomes

identify common mixtures

4.5, 4.7.5

By the end of this chapter you should be able to:

>>>

UNIT

context

3.1 There are a great number of mixtures. Soft drinks, Vegemite, coffee, milk, sea water, hair gel, air and sunscreen are a few examples of mixtures that we see every day. A mixture contains two or more chemically pure substances that may be separated using a physical process such as sieving or filtering. When a mixture is made, no new substances are formed—

it’s just that the particles of each substance are spread between the particles of the other substances. Look around your home and you will be surprised at the number of different mixtures that we use every day.

Solutions

solvent particles

Solutions are the most common type of mixture. A solution is formed when one substance (called the solute) dissolves in another (called the solvent). For example, when sugar is mixed with water, the solute is the sugar and the solvent is the water. We say that a sugar solution has been formed. One characteristic of solutions is that they are transparent (though they may be coloured)—no particles of the solute can be seen as they are too small and are spread evenly throughout the solvent. When a solution is made, the solute does not disappear. All of the solute added is still in the solution even though you can’t see it. The total mass of a solution is always equal to the mass of the solvent plus the mass of the solute. This is shown in Figure 3.1.1.

solvent

Fig 3.1.1

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solute

solute particles

Fig 3.1.2

A solution showing the distribution of solvent and solute particles

solution

Mass stays the same in solutions. We say that the mass is preserved.

Soft drink is a solution of sugar, flavourings and gas in water.

Fig 3.1.3

UNIT

3.1 Solutions can also be made by dissolving a liquid in a liquid, or a gas in a liquid. The table below gives some examples of solutions.

Solute

Solvent

Solution

solute particle

Carbon dioxide gas

Water

Soda water

Detergent

Water

Washing up water

Oil

Petrol

Two-stroke motor mower fuel

Germ-killing chemicals

Water

Disinfectant

Nail polish

Acetone (nail polish remover)

No common name

Pen ink stains

Methylated spirits

No common name

How come pizza still tastes good the next day? It seems the tomato paste base of pizzas does more than add to the flavour. Water trapped in tomato fibres does not mix with fat in the toppings (e.g. in cheese). Because the base does not absorb fat from above, the pizza tastes very similar to how it did the previous day.

If one substance can dissolve in another, we say that the substance is soluble. A substance that will not dissolve is called insoluble— for example, sand is insoluble in water.

Prac 1 p. 67

Prac 2 p. 68

Prac 3 p. 68

Concentration When a solvent (e.g. water) Snowy solutions contains a large amount of When a substance is solute (e.g. salt), the solution is dissolved, the freezing point of the solvent is said to be concentrated. The lowered. That’s why salt opposite of concentrated is is often sprinkled on dilute. Adding more solvent roads to prevent ice forming. For the same will dilute a concentrated reason, adding antifreeze solution, while adding more to a car radiator provides solute will make the solution protection—it makes it less likely that the water even more concentrated in the radiator will get If more and more solute is cold enough to freeze. added to a solvent, a point is reached where no more will dissolve. When a solution reaches this point, it is said to be saturated. Caramel is made from a saturated sugar solution.

concentrated solution

Fig 3.1.4

dilute solution

A concentrated and a dilute solution. Note the increased number of solute particles in the concentrated solution.

Suspensions A mixture of water and sand is not a solution, but is called a suspension. In a solution, the sizes of the solute and solvent particles are similar. In a suspension, the particles being mixed are bigger than those in the solution and, though they appear suspended initially, they will settle to the bottom of the container if left long enough. Some medicines are suspensions, as are some types of paint: they separate into different layers and therefore need to be re-mixed before use. The substance that settles out of a suspension is called the sediment. Sediment can be filtered out of a suspension, unlike the solute in a solution, which would pass through the filter.

Fig 3.1.5

A suspension showing the larger particles separating out by gravity

sediment

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>>>

Types of mixtures

Kidney dialysis

Colloids A colloid is in between a solution and a suspension. The particles in a colloid are bigger than those in a solution, but smaller that those of a suspension, and do not settle out as quickly.

When a person with kidney failure undergoes dialysis to clean their blood, a super-fine filter is actually removing soluble wastes from a colloidal solution of blood proteins.

Sols A sol is an emulsion where particles of a solid are spread throughout a liquid. Unlike a solution, a sol is not transparent. Blood plasma is an example of a sol in which solid blood proteins are spread throughout water. Blood is made up of blood plasma and blood cells (these will be studied in more detail later in Science).

dispersion medium

Emulsions

colloid particle

Fig 3.1.6

A colloid showing the relative particle sizes

An emulsion is a colloid in which particles of a liquid are spread throughout another liquid. Milk is an emulsion of liquid fat spread throughout water. Medicinal ointments are other examples of emulsions. Normally oil and water will not mix, but if detergent is added, it helps break up fat and oil drops into small particles that allow an oil/water emulsion to form. A chemical that helps fats form an emulsion is called an emulsifier. Detergent helps emulsify fats, as does bile in our intestines, making fats easier to digest. Many foods contain emulsifiers to stop fats separating into layers. Fig 3.1.8

Some paints are colloids, other are suspensions.

How then can we tell the difference between a solution and a colloid? The main difference is that a solution is clear, but a colloid is ‘cloudy’ due to light reflecting off the larger particles. The substance in which the particles are being spread is called the dispersion medium. It may be a solid, a liquid or a gas.

64

This results in several possible colloid combinations, which are described below.

Milk is an emulsion.

Fig 3.1.7

Brown dams and rivers Why do some dams and rivers always appear brown and never settle out clear? Though some of the brown colour may be explained by suspended soil, there may also be colloidal clay particles present, which do not settle out.

Foams A foam is a colloid made up of a gas mixed with a liquid. Shaving foam and fire extinguisher foam are examples.

Shaving foam is an example of a foam.

Fig 3.1.9

UNIT

3.1 Smoke Smoke is a example of a colloid formed when a solid (carbon) is spread throughout a gas (air).

Gels A gel is a colloid in which liquid particles (e.g. water) are held between the particles of a solid (e.g. gelatine). Jelly is a well-known example of a gel. Gels melt easily when heated.

Smoke is a colloid.

Fig 3.1.11

Mist A liquid spread throughout a gas may form a colloidal mist. Fog is a common example. Fog is a colloid.

Jelly is a colloid.

UNIT

3.1

Fig 3.1.12

Fig 3.1.10

[ Questions ]

Checkpoint Solutions 1 Clarify what is meant by the terms ‘solution’, ‘solute’ and ‘solvent’. 2 Draw a diagram to compare a solution, a solute and a solvent. 3 Choose the correct answer: When coffee powder is mixed with hot water, the water is the: A solute B solvent C solution

Worksheet 3.1 Representing mixtures Worksheet 3.2 Types of mixtures wordfind

4 In a solution, the particles of the solute cannot be seen because: A they are spread too thinly throughout the solvent B they have been destroyed by the solvent C they have been converted to solvent particles

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Types of mixtures 5 True or false? a In a solution, the solvent is always water. b A solute is always a solid. c A substance that is insoluble must be a solid. d When a mixture is made, new substances are not formed.

Concentration 6 Compare a concentrated and a dilute solution by listing their differences and similarities in a table. 7 Draw two diagrams showing a concentrated and a dilute solution, labelling the solute and solvent.

Suspensions 8 Explain why the particles in a suspension sink. 9 Identify the substance that settles out of a suspension in the following examples: a a mixture of chalk and water b muddy water c used engine oil that contains bits of worn metal 10 State two examples of suspensions.

Colloids 11 Explain why a colloid is said to be in between a solution and a suspension. 12 Identify three classes of colloids and the dispersion medium of each. Give an example of each and construct a table to display your answer.

>>> 19 Explain why some medicines need to be shaken before using them. 20 Propose a method to separate the solid from the liquid in a suspension by researching how some suspensions are separated in industry. 21 Outline how a torch could be used to test for a colloid. 22 Explain how detergent changes an oil/water suspension into an emulsion. 23 Classify each of the following as a solution or suspension: glue, saline (salt water), cream, whisky, muddy water, sunscreen 24 Draw a diagram to compare the particles in a solution, an emulsion and a suspension. 25 Explain why is it important that fertilisers are soluble. 26 Describe a method that would enable you to distinguish between a solution and a colloid.

Analyse 27 Copy and complete the following table after referring to Figure 3.1.1.

Mass of solvent (g)

Mass of solvent (g)

100

12

60

90 65

Think 13 Graffiti remover is used to wash paint from a wall. Classify the paint as solvent, solute or solution. 14 Identify two examples of common substances that are: a soluble in water b insoluble in water 15 Which of the following is not a solution? A Coke B salt water C sand in water 16 Describe how a dilute solution is formed. 17 Name a solution in which there are many solute particles and few solvent particles. Define the type of mixture that this represents. 18 Design an experiment to determine whether cordial is a suspension or a solution. In your experiment, you should: a outline a clear aim for the experiment b identify conditions (variables) that will change or should be kept constant c suggest ways of reducing any wastes that might be made in the experiment

66

Mass of solution (g)

180

Skills 28 To test the solubility of an unknown solid, students placed a solid into 200 mL of water. They then decided to see if solubility changed with increasing temperature of the water. The results are shown in the table. Temperature (°C)

25

30

45

55

65

70

75

Amount of solid (g)

17

20

32

40

46

49

52

a Draw a line graph showing the relationship between the amount dissolved and the temperature of the water. c Predict the amount of solid that could be added to water at 35°C and 85°C. d State a conclusion to the investigation.

UNIT

3.1 [ Extension] Investigate 1 a Define an alloy. b Explain why an alloy is a mixture. c Identify some alloys that may be found around the home. d Relate the use of each alloy to its properties, such as lightness or resistance to rust. 2 Using the Internet or other resources, identify the components of a soft drink. Compare the ingredients of diet and normal soft drinks.

Surf Find out more about the following science applications by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools selecting chapter 3, and clicking on the destinations button. 4 Washing powders can come in concentrated form. Investigate how this is done. 5 Salt is used to dissolve ice on roads, making them safer. Create a brochure to explain to drivers why the salt is used and how it works.

Action 3 Determine whether equal amounts of washing powder will dissolve in cold and hot water. a Design a test involving stained material to compare the results of washing in both types of water. b Identify any steps in your method that might be dangerous, e.g. working with hot water, spilling washing powder onto skin. Describe how you could perform these steps safely. c Carry out your test and report on your results. DYO

UNIT

3.1

[ Practical activities ] Testing solubility in water Aim To test the solubility of various substances

Prac 1 Unit 3.1

in water

Equipment Salt, sugar, ground-up coloured chalk, copper sulfate, flour, soil, household and other substances as provided by your teacher, test tubes, test tube holder, water, rubber stopper(s), spatula(s), safety glasses

Method 1 Use a spatula to place a very small amount of a substance into a test tube. 2 Half fill the test tube with water. 3 Place a rubber stopper in the top of the test tube and shake it in an attempt to dissolve the substance.

4 Return the shaken test tube to the test tube rack and observe it. 5 Repeat steps 1 to 4 for the other substances, recording your observations.

Questions 1 Classify all the substances tested as soluble or insoluble. 3 Explain why was it important to use a very small amount of each substance. 4 Identify which substance appeared to be: a most soluble b least soluble

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>>>

Types of mixtures

Temperature and solubility Aim To find out how temperature affects the solubility of two different chemicals

Prac 2 Unit 3.1

Equipment Test tubes, test tube holder, test tube rack, copper sulfate, calcium acetate, spatula, safety glasses

5 Again swirl the test tube and try to dissolve more chemical. 6 Place the test tube in the rack and leave it to cool. Observe what happens as it cools. 7 Repeat steps 1 to 6 using calcium acetate.

Questions

Method 1 Fill the test tubes with cold water to a depth of 5 cm.

1 Describe the effect (if any) of heat on solubility.

2 Use the spatula to add a tiny amount of copper sulfate to a test tube, and gently swirl the test tube to dissolve the chemical.

2 Explain the difference in solubility between copper sulfate and calcium acetate.

3 Continue adding more chemical until a small amount remains undissolved in the test tube. 4 Gently heat the solution for about 10–20 seconds. Do not boil it. Fig 3.1.13

3 Calcium acetate and air have similar solubilities. Use this information to explain the bubbles that are seen as water is first heated. 4 Describe what happens as a saturated solution cools. (You may have to leave your test tube of copper sulfate solution overnight before answering this question.) 5 Draw diagrams to show what happens to the solute and solvent particles as a saturated solution cools.

copper sulfate/water

Bunsen burner

water heat-proof mat

sugar cube

Surface area and solubility Prac 3 Unit 3.1

Aim To examine whether surface area has any

Fig 3.1.14 4 Swirl both beakers for 10 seconds in an attempt to dissolve as much of the sugar as possible.

effect on the rate of dissolving

Equipment Two sugar cubes, two beakers, water

Method 1 Place an equal amount of water (e.g. to a depth of 5 cm) at the same temperature in each beaker.

68

sugar crystals (crushed sugar cube)

Questions 1 The crushed cube has greater surface area (imagine it spread over the bottom of the beaker). Describe what effect increasing the surface area of a solute has on the rate of dissolving.

2 Crush one of the sugar cubes into separate crystals.

2 Describe why all of the crushed cube is used rather than some of it.

3 Place the whole cube in one beaker and the crushed cube in the other.

3 State reasons for keeping water level and temperature the same in both experiments.

UNIT

context

3. 2 The separation of mixtures can give us pure substances. To obtain pure substances, we often need to remove insoluble substances from a mixture. Since each part of a mixture keeps its own properties we can use several methods. This is important as it is used in industry to purify metals, and in other activities, like panning to separate gold from river sand, and wine making to remove sediment from old bottles of wine.

A sieve in action

Fig 3.2.1

Decanting Decanting is a simple method of separation that may be used with suspensions. The mixture is left long enough for most of the sediment to collect at the bottom of a container and the liquid above the sediment is carefully poured into another container. Old wines contains sediment which may be re-spread throughout the wine if a bottle is moved too much during pouring. To avoid this happening, wine is often decanted from the bottle into a decanter before pouring.

Sieving Sieving is useful when there are different-sized particles in a Whale of a filter Instead of teeth, the baleen mixture. If you accidentally add whale has a filtering too many chocolate chips to a device composed of 300 mixing bowl containing flour, plates of whalebone you could sieve the mixture so (baleen) hanging from the roof of its mouth. These that the finer flour passes baleen filter small through the sieve while the plankton called krill from chocolate chips are collected sea water. The whale then uses its huge tongue to on the sieve. Crushed ore may wipe the filter clean before be sieved to collect pieces that swallowing the krill. require further crushing prior to extraction of metals. Another common use for sieving is in fishing nets with various-sized holes to catch legal-sized fish.

Filtration Filtration is just a very fine sieving process. Instead of a sieve, a special filter is used. One type of filter used in the laboratory is filter paper, which contains millions of tiny holes that allow particles in a solution to pass through, but not the larger particles. Filter paper Funnel Residue (solid material left in the filter paper) Filter stand Beaker

Filtrate (liquid that passes through the filter paper)

Fig 3.2.2

The filtering process is used to separate solids from liquids in the science laboratory.

69

>>>

Separating insoluble substances Coffee plungers, tea bags, dust masks, vacuum cleaners, car fuel systems, spa and swimming pool filters are all filters. The substance that is trapped by the filter is called the residue, and what passes through is called the filtrate. Worksheet 3.3 Application of filtering at home

Similarly, a laboratory centrifuge holds special test tubes at an angle so that the heavier particles in a liquid are forced to the bottom of the tubes. Blood can be separated using a centrifuge. Milk and its cream can be separated this way too.

Prac 1 p. 73

Gravity separation If a mixture containing water and particles of different weights is stirred or shaken, the heaver particles will tend to move towards the bottom of the container. This is how panning for gold works—tiny (but heavier) specks of gold sink to the bottom of the pan, so they remain when the lighter gravel is washed off.

Centrifuging Another method involving the movement of particles is centrifuging. The spin drier in a washing machine is a type of centrifuge. When the spin cycle activates, the drum rotates rapidly, forcing the clothes and water against the drum wall. The walls contain small holes that allow water to pass through them and be pumped out, leaving the clothes ‘spun dry’.

wet clothes

spinner

spin

A laboratory centrifuge separating blood into layers

Magnetic separation Scrap iron may be separated from non-magnetic materials using a powerful electromagnet suspended over a conveyer belt. The electromagnet may be turned on and off to release the collected iron.

water forced out through small holes

to basin

A washing machine spin dries clothes using a centrifuge action.

70

Fig 3.2.3

Fig 3.2.4

Fig 3.2.5

Magnetic separation in industry

Prac 2 p. 73

Electrostatic separation

Froth flotation

Industrial chimneys may contain electrostatic precipitators, which remove waste products by charging particles as they move up a chimney. The particles, once charged, are attracted to metal plates (also charged) and are prevented from being released into the atmosphere.

Froth flotation is used in the processing of minerals. During copper production, rocks containing grains of copper must first be crushed and ground to a fine powder—this is called liberation. Once liberation has occurred, the powder is mixed with water and special chemicals in flotation cells. Air is then blown into the mixture to produce bubbles of froth. Chemicals in the mixture stop the bubbles bursting, and help the copper stick to the bubbles. The unwanted part of the powdered rock, called gangue, falls to the bottom of the flotation cells. Copper ore, containing a high proportion of copper, may then be skimmed from the top of the flotation cells.

charged wires

charged particles collect on plate

+ + +

+ + +

+

–

+

–

+

–

– – –

–

Froth flotation of copper ore

charged plate

UNIT

3.2

Fig 3.2.7

– –

smoke

An electrostatic precipitator

UNIT

3.2

Fig 3.2.6

[ Questions ]

Checkpoint Decanting 1 Draw a diagram to clarify how you could decant water from a sand/water mixture.

Sieving 2 Explain a use of sieving and how this process works.

Filtration 3 True or false? a Filtration may be used to separate a solute from a solution. b Filtrate is what passes through a filter. 4 Explain what the residue is in filtration.

Centrifuge 5 Describe how the spinning of a centrifuge causes separation.

Froth flotation 6 Outline the process of froth flotation by placing the following terms in order from first to last: chemicals added, skimming, liberation, air blown in. 7 Define gangue and explain where it comes from.

Think 8 Identify and explain two uses of filtration in your home. 9 Draw a cross–section diagram of the filtration method used in the laboratory. 10 A quarry produces a mixture of small and large crushed rock pieces. Explain the basic method that may be used to separate the small and large pieces. 11 During a heavy downpour, rain washes only the heavier stones from a driveway into a pile at the lowest point of the driveway. Identify and explain which separation method has occurred. >>

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Separating insoluble substances

>>>

Separation method

Brief description

Example

Decanting

Liquid gently poured from one container into another, leaving sediment at the bottom of the original container.

Wine from an old bottle poured into a carafe, leaving sediment behind.

12 Copy and complete the table above to summarise all separation methods in this section. Add as many lines as you need.

17 Propose reasons why the paper element in an oil filter is folded as shown here.

13 Identify some household appliances that contain a centrifuge. Examine other areas in the house where this method of separation could be used 14 Specify a separation method to assist with the following problems: a A container of small metal nuts and bolts is spilt on the grass near a workshop. b An orchardist wishes to separate under-sized fruit before packing fruit for market. c An industrial chimney belches unacceptable amounts of waste into the atmosphere. d An apiarist needs to remove honey from honeycomb before bottling.

paper element

15 Explain why salt can’t be separated from salt water by using filter paper. Clarify your answer using diagrams showing the sizes of water and salt particles. 16 Explain why test tubes in a centrifuge are at an angle and not vertical.

Fig 3.2.8

The inside of a car’s oil filter

[ Extension ] Create 1 Design a simple device to stop leaves entering stormwater pipes after being washed down the spouting of a roof. Specify the separation technique that has been used.

Investigate 2 a Kidney dialysis is an important application of the separation of materials. Explain what the process is and describe the benefits to our society’s health. b Write a letter to a local dialysis centre and invite a representative to explain the process to the class.

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3 Recycling aluminium, glass and plastic containers involves placing them together. Design a method to successfully separate these materials. Compare an industrial method such as a local recycler might use with your class method. 4 Examine the possibility of placing sugar and powered milk into a tea bag so that a cup of tea could be made even more quickly. Design a newspaper advertisement to promote the new product.

UNIT

3.2

[ Practical activities ] Filtration Aim To filter a mixture to obtain a filtrate and

Prac 1 Unit 3.2

UNIT

3.2

a residue

Equipment Crushed (powdered) coloured chalk and copper sulfate mixture, conical flask, beaker (100 mL), funnel, filter paper, stirring rod, safety glasses

Method 1 Place the powdered mixture into the beaker, and add about 50 mL of water.

filter paper

3 Fold the filter paper as shown in Figure 3.2.9 and place it in the funnel. Then place the funnel in the conical flask.

funnel residue

conical flask

4 Tip the water/powder mixture into the filter paper.

2 Use the stirring rod to mix the water and powder as best you can.

filtrate

Fig 3.2.10

Assembled filtering apparatus

Questions 1 Contrast the size of the copper sulfate particles with that of the chalk particles. Explain your observation. 2 Produce a magnified diagram explaining how the filtrate is trapped by the filter paper. Use different symbols for the solute and solvent particles. 3 Recommend a method that might recover the copper sulfate powder from the filtrate.

open out

Fig 3.2.9

Fig 3.2.11

Magnetic separation

Method for correctly folding a filter paper plastic bag

Magnetic separation Aim To separate a mixture using a magnet Prac 2 Unit 3.2

magnet

Equipment

paper

A mixture of sand and iron filings, a sheet of newspaper, a magnet in a plastic bag, empty container for iron filings, a sheet of paper

newspaper

Method 1 Place the sheet of newspaper on a bench, then place a small pile of the sand/iron filings mixture on top.

Questions

2 Spread the mixture into a flat pile and place a sheet of paper on top.

1 Explain why the sheet of paper was placed on top of the mixture.

3 Use the magnet in the plastic bag to carefully separate the mixture, placing the separated iron filings in a clean container as you go.

2 Explain why the magnet was placed in a plastic bag. 3 Propose how a similar technique could be used in industry.

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>>>

UNIT

context

3.3 Soluble substances are more difficult to separate out of mixtures than are insoluble substances. The methods used rely on the basic properties of matter, and are used in many industrial applications. These include making salt from sea water, purifying water for drinking, and even in forensics for working out who committed a crime.

Evaporation and crystallisation A filter cannot separate the solute particles in a solution, but crystals of the solute will remain behind if the solvent is left to evaporate. Boiling the solution can speed up the evaporation process. In large-scale salt production, giant salt pans allow evaporation using the heat Prac 1 p. 77 energy from the Sun. Fig 3.3.1

Large-scale salt production in a salt pan

Distillation Distillation also involves evaporation, but this time the evaporated liquid, called the distillate, is collected. Again, what remains in the original container is called the residue. Tap water contains several other substances, and so strictly speaking is not pure. Distillation is used to obtain pure or distilled water. A laboratory distillation apparatus is shown in Figure 3.3.2.

condenser

flask solution flask cold water out

cold water in

Fig 3.3.2

distillate

A laboratory distillation apparatus

A desert survival technique involves the collection of distillate using a sheet of plastic to trap water distilled from the ground or plants. Distillation is also used in the production of whisky (hence the term ‘distillery’) and perfume.

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larger rock

larger rock small rock plastic sheet

UNIT

3. 3 Charcoal contains many fine pores that allow it to absorb many dangerous gases, and so is used in gas masks and breathing filters. Packages of food that must be kept free of moisture sometimes contain small sachets of silica gel, which can absorb nearly half their weight in water.

vegetation

Fig 3.3.3

Life-saving distillation in the desert

Many different substances (called fractions) exist in crude oil. Fractional distillation uses the fact that these substances boil at different temperatures. This allows them to be separated into petrol and other substances as shown in Figure 3.3.4. Fig 3.3.4

Prac 2 p. 77

Silica gel separates water from materials by absorbing the moisture.

Products of crude oil distillation are obtained at different temperatures.

Chromatography

crude oil IN

0–90°C

Fig 3.3.5

Chromatography is a technique that may be used to separate colours in inks, food dyes and other mixtures of colours. A medium such as blotting or filter paper containing a spot of the mixture is placed in contact with a solvent (e.g. water). Because different colours move at Prac 3 different rates through the medium, they p. 78 separate along the medium.

petroleum gases aviation gasoline petrol kerosene, jet fuel

400°C

Worksheet 3.4 Using chromatography heating oil diesel fuel lubricants, waxes

500+°C

PREMIUM MOTOR OIL

furnace oil, bitumen

Absorption Absorption occurs when a material is ‘taken in’ or ‘swallowed’ by another. A kitchen sponge absorbs water. Special chemicals may be used to absorb particular substances from a mixture.

Fig 3.3.6

Paper chromatography can be used to separate the colours in ink.

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Separating soluble substances

UNIT

3.3

[ Questions ] 13 The small silica gel packets inside various products carry a notice saying: DO NOT EAT. Propose why this warning is present.

Checkpoint Evaporation and crystallisation 1 Copy and complete: When a solution evaporates, c_____ of solute may be left behind.

14 Plan a sequence of steps for producing fresh water from sea water.

2 Describe what a salt pan is and what it is used for.

15 Identify a separation technique for each of the following situations. a A teacher has smelly feet. b Joe was cooking and dropped a bag of salt into a bowl of water. He wants to get the salt back, but not the water. c Mary wants to recycle water from her washing machine to make drinking water. d The police have three pens and want to find out which one was used to write an anonymous letter. e James want to breathe clean air, not paint fumes, while painting his house.

Distillation 3 Describe how distillation is different to evaporation. 4 Sketch a diagram to illustrate the process of distillation. Explain what is happening at each step. 5 Identify three examples where distillation is used. 6 Define a fraction in distillation. 7 Identify three different fractions and their uses from Figure 3.3.4.

Absorption 8 Identify an example of something that absorbs a: a liquid b gas

16 Explain why each of the separation techniques identified in question 15 would work.

Chromatography 9 Clarify the types of mixtures that chromatography is used to separate. 10 Explain how different colours move in chromatography.

Investigate

Think 11 Copy and complete the table below to summarise the separation methods in this unit.

Separation method Evaporating

[ Extension ]

Brief description The mixture is boiled so that the solvent evaporates. This will leave behind the solute.

Example Salt from sea water

1 Water can be described as ‘hard’ or ‘soft’. a Explain the difference between ‘hard’ and ‘soft’ water. b Form a team and design an experiment that will test the hardness of the tap water in your home. c Determine whether the water tested is DYO hard or soft. 2 a Investigate how you would make a solar still for use if you had run out of water in a desert area. b List the equipment that you would require. 3 When a cube of sugar is added to a clear glass of water you notice that there is a wavy area close to the dissolving cube. Over time this disappears. Explain this unusual feature.

12 Explain why salt is obtained from salt pans, rather than from boiling sea water.

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4 Research why air bubbles form on the inside of a beaker when it is heated.

UNIT

3.3

[ Practical activities ] Separation by evaporation

Prac 1 Unit 3.3

UNIT

3.3 A simple distillation

Aim To collect the dissolved substances from soft drink using evaporation

Prac 2 Unit 3.3

Aim To collect a sample of pure water using distillation Equipment

Bunsen burner, salt solution or soft drink, heat-proof mat, evaporating basin, tripod, gauze mat, safety glasses

Bunsen burner, gauze mat, heat-proof mat, conical flask, tripod, watch-glass, wooden test tube holder, salt solution, beaker, 3 paperclips, water, safety glasses

Method

Method

Equipment

1 Place a small amount of solution in the evaporating basin (half to one-third full) and place it on the gauze mat as shown here.

PART A The distillation 1 Assemble the apparatus as shown in Figure 3.3.8.

Fig 3.3.7 watch-glass evaporating basin gauze mat flask tripod

solution

beaker

heat-proof mat

Fig 3.3.8

2 Heat the solution, but turn off the Bunsen burner just before the last drop of water disappears (the heat remaining in the basin will be more than enough to finish evaporating the water). 3 Allow the crystals to cool. You may wish to stick a sample in your book under a piece of contact adhesive.

Questions 1 Describe what you saw as the water evaporated. 2 Explain why it is important to stop heating when the water is just about gone. 3 Predict where the water went.

2 Use the watch-glass and beaker to collect distilled water. Save some of the salt solution for Part B of this activity. PART B Testing the distillate 1 Unfold the paperclips. 2 Dip one paperclip in the salt solution and then hold the dipped end of the paperclip in the blue flame of a Bunsen burner. What colour flame is produced? 3 Dip another paperclip in plain water and repeat the ‘flame test’. 4 Dip a third paperclip in your distillate and repeat the ‘flame test’.

Questions 1 Explain what the flame tests tell you about the distillate. 2 Present a reason for not using the same paperclip for all three flame tests.

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Separating soluble substances

Chromatography of Textas and Smarties Prac 3 Unit 3.3

Aim To separate the colours in Smarties or ink Equipment

Water-based Textas, Smarties of various colours, eye dropper, water, beaker, filter paper

Method

4 Repeat step 3 if necessary to spread rings of colour from the dot. Be patient. 5 Try different-coloured dots. 6 Instead of Textas, use the dye from Smarties. Place a drop of water on a Smartie to extract its colour, then use an eye dropper to collect some. Place a drop of dye in the centre of a piece of filter paper and repeat steps 1 to 5.

1 Using a water-based Texta pen, make a dot in the centre of a piece of filter paper.

7 Compare results for different brands of felt-tipped pens or Smartie-type confectionery.

2 Place the filter paper on top of the beaker.

Questions

3 Using the eye dropper, place a drop of water on the dot of ink. Fig 3.3.9

1 Present a list of the colours in each Texta and Smartie you tested. 2 Explain why different colours spread at different rates.

mL

3 Assess whether this experiment could be used to decide if a lolly is a genuine Smartie. 1

2

eye dropper/water filter paper

beaker

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UNIT

context

3. 4 Our water supplies and waste water are two mixtures that need to be treated very carefully. Removing unwanted impurities from drinking water is important to our health. Removing impurities from waste water is important to the health of the environment.

Water supply You may be surprised to learn that rainwater is a mixture, and is by no means a pure substance. Rain is produced when water evaporates from oceans, lakes and other bodies of water and even from plants and soil. Because it has been in contact with substances that dissolve in it, rainwater is a dilute mixture that must be treated before being supplied to our homes. Water from domestic rainwater tanks is generally not treated, as the potential for contamination is slight.

The rainwater that we normally drink has passed through an extensive water supply system, however, and must be treated to ensure it does not contain harmful levels of chemicals or bacteria. Treatment may involve the dissolving of the following substances in the supply.

Chlorine Chlorine may be added in liquid or gas form to kill germs that can cause diseases such as gastroenteritis (‘gastro’ for short).

Water consumption The World Bank estimates that every person needs 5 litres of water for drinking and cooking per day, and an extra 25 to 45 litres per day to keep clean and healthy. It is estimated that Australians use around 57 litres each day— quite a luxury compared to those in less fortunate countries.

Fluoride Fluoride is added to help prevent tooth decay in consumers of the treated water.

Lime and soda ash The chemicals lime and soda ash may be used to ensure the water is at a neutral pH, like a ‘waterbalanced’ swimming pool. You will learn more about acidity and pH levels when you study acids and bases later in Science.

Electrolytes Electrolytes trap suspended particles by causing them to clump together and fall to the bottom of the tank as sediment. These clumps are called floc, and the process is called flocculation. Figure 3.4.2 shows the basic stages of water supply. The service reservoir is an artificial structure that stores water for use during peak demand times. The stand pipe is used to provide increased pressure to high service areas.

Fig 3.4.1

Water is stored in reservoirs for up to five years to allow waste to settle out naturally before further treatment.

Prac 1 p. 84

Prac 2 p. 84

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Water supply and sewage

catchment area

storage reservoir

chlorination

fluoridation

pumping station

stand pipe

service reservoir

water mains

city houses in high areas

industry

homes water meter

schools

sewage

treatment

ocean

The flow of water from catchment to sewage treatment

80

Fig 3.4.2

UNIT

3.4 Sewage Many people get the terms ‘sewage’ and ‘sewerage’ mixed up. Sewage is the waste and water mixture that humans put down sinks, drains and toilets in their homes and in industrial processes. Sewerage is the word used to describe the network of pipes into which sewage passes. Some homes are connected to a septic tank, where sewage is broken down by bacteria and is released into the soil, leaving a thick sludge in the tank that must be removed periodically. Because a septic tank depends on bacteria, chemicals that may kill bacteria should not be allowed to pass into the tank. Most houses in city areas are connected to the sewerage network that leads to treatment plants and eventually to the ocean.

spouting

vent pipe downpipe bath

laundry sink kitchen

toilet

storm water system

gully trap sewerage system

Sewage treatment plants A typical sewage treatment plant involves the activated sludge process. Sewage entering the plant has objects removed from it using a screen to sieve

Fig 3.4.4

Household connections to the sewerage system

Fig 3.4.3

A treatment plant showing the large settling tanks

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Water supply and sewage

blowers

aeration tank sewage in

screen

chemicals added

UV lamps outfall settling tank

pebble filter

ocean

sludge removed pump

The activated sludge process

out large objects. Then it flows to an aeration tank, where air is pumped into the tank to feed bacteria that help break down the sewage by feeding on it. The gas produced by bacteria as they break down sewage may be collected and used to power turbines for the aerators.

UNIT

3.4

Poo-burgers

once A Japanese scientist made rs rge bu promoted ham as an age sew d ate tre ng usi ly food. environmentally friend Not surprisingly, the ’ so-called ‘poo-burgers never took off.

[ Questions ]

Chemicals are also added to convert dissolved wastes into solids, which then fall to the bottom of the tank. The next stage is the settling tank, where gravity separation results in bacteria and other solids settling at the bottom in a thick sludge. Some of the bacteria may be returned to the aeration tank to help break down sewage. Next, the sewage passes into pebble bed filters where suspended solids are removed. UV light or chlorination is used to disinfect the sewage before it is released into the ocean. The sludge is removed and air dried before being stored for several years, after which some of it may be sold for use in soil and fertiliser products. Worksheet 3.5 Using water wisely

Prac 3 p. 84

Checkpoint Water supply 1 Rainwater is evaporated water. Describe some places where this water has been evaporated from.

Sewerage 6 Distinguish between sewage and sewerage.

2 Classify rainwater as either a mixture or a pure substance.

7 Identify three items connected to the sewerage system in your house.

3 Account for how rainwater picks up impurities.

8 Explain what breaks down sewage in a septic tank.

4 When treating water, which chemical is added to: a kill germs? b prevent tooth decay? 5 Explain the term ‘flocculation’.

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Fig 3.4.5

9 Explain how the septic tank helps separate sewage. 10 Explain why air is blown into one of the tanks at a sewage treatment plant.

[ extension ]

Think 11 Explain why more chlorine is required per litre in swimming pools than in our drinking water. 12 The catchment of a reservoir is the hills, creeks and rivers around the reservoir. Propose why it is important to look after the catchment of a water supply. 13 The forest in a catchment is often said to be like a natural filter. Explain what you think this means. 14 Justify why it is better to wash a car on your lawn than on the road. 15 Propose three ways that the sludge from a sewage treatment plant could be recycled or reused. 16 Predict what could happen if sewage was not treated before being released into rivers or the ocean. 17 Identify each separation technique used in the activated sludge process and describe what it removes from the sewage. 18 Propose a reason why basins around the house have ‘S bends.’ Fig 3.4.6

UNIT

3. 4

Why does this basin have an ‘S’ bend?

basin

Create 1 Design a house that would assist people in country areas to use their house roofs to collect and use rainwater. 2 Why should people save water? Design and present a poster to promote reducing water waste in your home.

Investigate 3 Research and compare the amount of water used in various industrial processes (e.g. making paper, soft drinks, recycling). Present the data as both a table and a column graph. 4 Research the history of the sewerage system and its effects on public health. 5 Explain the term ‘eutrophication’ and discuss its importance to farmers. 6 Research the composting toilet and produce an advertisement to sell this product. In your advertisement you must: a Outline how the composting toilet works. b Discuss its advantages and benefits. 7 a Define the term ‘acid rain’. b Describe regions of the world where acid rain is a problem.

Action 8 Organise a representative from a local water treatment facility or sewage treatment plant to visit your class and talk about the importance of clean water.

Surf

to sewerage system

9 Research the history of water treatment in Australia by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools selecting chapter 3, and clicking on the destinations button.

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Water supply and sewage

UNIT

3. 4

[ Practical activities ] Water purification

Testing flocculation chemicals

Aim To purify some dirty water for drinking Prac 1 Unit 3.4

Prac 2 Unit 3.4

Equipment Ice-cream or margarine container, sand, stones, muddy water, beakers (2 x 250 mL), tripod, stirring rod

Method 1 Prepare the container containing sand and stones as shown in Figure 3.4.7. Fig 3.4.7

Aim To identify some chemicals that cause flocculation

Equipment A 250 mL beaker of muddy water, filter paper, conical flask, funnel, stirring rod, some of the following: copper sulfate, iron(II) chloride, copper chloride, sodium carbonate, sodium bicarbonate, ammonium sulfate, magnesium sulfate, calcium sulfate, safety glasses

Method 1 Let the muddy water stand for a few minutes to separate out some sediment. 2 Decant some of the water into a filtering apparatus.

muddy water

sand layer stones layer

margarine or ice-cream container small hole in container

beaker

3 Take the filtrate and add a few drops of one of the chemicals to be tested, stirring briefly. Note whether any flocculation occurs. 4 Test the other chemicals in this way.

Questions 1 Identify which chemical produced the most flocculation. 2 State which type of particles you think the chemicals that caused flocculation reacted with—those in suspension or those in solution. Explain why. 3 The ‘clumped chemicals’ are referred to as the flocculent. Explain how you could remove the flocculent.

2 Pour half of your muddy water into the container, and keep half for later comparison. 3 Allow the filtrate to drain into the clean beaker long enough to collect a good sample of ‘purified water’.

Questions 1 Describe the effectiveness of the sand/stones filtration. 2 Design a method that could improve the purification (e.g. by adding stages to the basic method).

Separating artificial sewage Prac 3 Unit 3.4

Equipment

DYO

Artificial sewage mixture provided by your teacher (containing things like bread, chopped vegetable scraps, soil, sand, detergent, oil, grass clippings, coffee, paper, plastic etc.), other general science equipment depending on your method

Method 1 Design a method of ‘treating’ your ‘sewage’ sample. There may be several stages to your process. 2 Keep a small sample of treated and untreated ‘sewage’ for comparison. 4 Clarify your process by describing the stages and their effectiveness.

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Chapter review [ Summary questions ] 1 Identify four mixtures found in the home. 2 Paint is removed from a brush using turpentine. Identify: a the solvent b the solute 3 Describe how a solution and a suspension are different. 4 Copy and complete: A substance that will not dissolve is said to be _____. 5 Give the correct scientific term for a: a weak solution b strong solution 6 Outline the process of: a sieving b filtration 7 Explain how crude oil is separated into several types of chemicals. 8 Identify three substances obtained from crude oil and specify two uses for each substance. 9 Identify the separation method used in gold panning.

23 Explain how a coffee filter separates coffee from the ground coffee beans. Propose a method to separate the coffee from the ground beans if you ran out of coffee filters. 24 Predict which would dissolve faster in water—a gram of cube sugar or a gram of castor sugar. Explain your answer. If you were performing an experiment to test this prediction, describe which factors must be kept constant. 25 A mineral water company requires a scientific demonstration to show that their water contains less dissolved mineral than its closest competitor. Design an experiment that could be shown on television. 26 If you suspected that the contents of a bucket contained sand, clay and salt all mixed with water, explain how you would: a remove all impurities in one attempt b remove only the sand c remove both the clay and the sand 27 Design a method by which you could check the amount of sugar dissolved in a certain brand of cordial.

10 Identify three uses for a centrifuge. 11 Identify the separation method in which charcoal is used. Describe how this technique works. 12 Define and explain chromatography. Identify how it is used in forensic science. 13 State what ‘liberation’ is in mineral extraction. 14 Explain how rainwater can be used to pick up contamination. 15 Explain why fluoride is added to our water supply. 16 Explain why water in reservoirs is stored for several years before further treatment. 17 Define ‘floc’. 18 Explain why blowers are used in an aeration tank at a sewage treatment plant. 19 Describe how water may be disinfected in the final stages of treatment.

[ Thinking questions ] 20 Explain what happens to a soluble solid when it dissolves in a liquid. 21 Water is a solvent for many substances. Identify suitable solvents for: a oil paint b grease c nail polish 22 Detergents are used when oil spills occur at sea. Discuss whether the detergent really cleans the water.

[ Interpreting questions ] 28 Study the following data and answer the questions that follow. Volume of water used = 100 mL Temperature of water (°C) Maximum amount of copper sulfate that would disolve (grams)

0

20

40

60

80

100

18

22

29

38

50

78

a Identify the solvent and solute. b Clarify what happens to the solubility as the temperature is increased. c Account for your observation in part b. d If the volume of water was doubled, predict what would happen to the amount of solute that could dissolve at 20°C. Explain your answer. e Identify the type of graph that would best represent these results. f Draw a diagram to illustrate the experimental set-up you would use to collect the salt. Worksheet 3.6 Mixtures crossword Worksheet 3.7 Sci-words

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Cells Key focus area:

4.1, 4.8.1, 4.8.3, 4.8.4, 4.8.5

Outcomes

>>> The history of science

By the end of this chapter you should be able to: explain what a cell is, using examples identify the parts of a cell and their function use a microscope correctly and prepare microscope slides explain the difference between unicellular and multicellular organisms, giving examples describe how cells reproduce describe some specialised cells and how they can arrange into tissues, organs and systems in living things

Pre quiz

describe the main systems of the human body.

1 The photograph at right shows a sperm from a man about to fertilise an egg from a woman. How are photographs like this obtained?

2 What do you think the word ‘cell’ means?

3 What do humans and plants have common?

4 What type of creatures can you find lots of in a drop of water?

5 What body systems do we have?

4

3.1 UNIT

UNIT

context

4.1 Humans have always wondered what things are made up of. We pull apart pens and calculators to see what is inside. We try to look closer and closer to find out what tiny parts are inside larger objects. The microscope was invented to allow scientists to view extremely small things that are normally not able to be seen.

Without the microscope, scientists would not be able to study the tiny building blocks of life that we call cells. Knowledge about cells and their structure has allowed many important advances to be made in science and medicine. ‘Microscopic’ is a term you have probably heard before. It doesn’t just mean an object is small, it means so small that the only clear way of seeing it is by using a microscope.

just one lens. A compound microscope, commonly used in schools today, contains two or more lenses. The compound microscope was invented by Hans Janssen and his son Zacharias and separately by Hans Lippershey in 1609, though some history books suggest that Janssen’s invention may date back to 1590. In 1665, Robert Hooke designed a prototype of the modern compound light microscope. The light microscopes of today are used to magnify specimens by as much as 1500 times.

Parts of the microscope A monocular microscope is a type of compound microscope and has a single eyepiece, like the one shown in Figure 4.1.2.

eye piece (ocular lens)

The light microscope A microscope is an instrument used to obtain magnified images of small objects. A magnifying glass is what we call a simple microscope, as it contains Hooke’s microscope

coarse focusing knob

barrel

Fig 4.1.1 arm objective lenses

clips

fine focusing knob

stage diaphragm mirror

base

Fig 4.1.2

A monocular compound light microscope

A stereo microscope is one that has two eyepieces. These are more expensive than single-eyepiece microscopes, but provide a clearer and more three-dimensional image.

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The microscope

Lowering a cover slip onto a wet mount

A stereo microscope

Fig 4.1.3

Using a microscope Correct microscope use can help you see fantastic images that others may miss, so pay careful attention to the following. What you place under a microscope is called a specimen. What you see when you look through the eyepiece is called the image. To obtain a good image, we sometimes need to prepare the specimen first, by doing the following: • Obtain a thin section by scraping, squashing, peeling or slicing the object. This allows more light to pass through the specimen into the microscope and to your eye. • Place the specimen onto a glass microscope slide. Stain the specimen to make it darker and easier to see. • Secure the specimen so it doesn’t move easily. One way to do this is by using a wet mount. This involves placing the specimen on a glass microscope slide with a drop of water. Gently lower a thin glass cover slip onto the specimen and water by placing one edge of the cover slip down first. Use a piece of filter paper to soak up any excess water.

88

Fig 4.1.4

Sometimes air bubbles can become trapped under the cover slip and appear as circles when viewed under a microscope. Do not confuse air bubbles with what you are really trying to observe. Once the specimen has been prepared, you are ready to look at its image using a microscope. Follow these steps to protect the both the microscope and the slide from damage and to obtain a clear image. 1 Place the prepared slide on the stage and secure it using the clips. 2 Some microscopes have a built-in lamp. If your microscope doesn’t, then face it towards a light source (this could be a microscope lamp or window). Adjust the mirror to project light through the stage to the specimen. 3 Select the objective lens with the lowest magnification and rotate it into place. (It is easier to start viewing with low magnification.) 4 While looking from the side (not through the eyepiece), adjust the coarse focusing knob so the objective lens is just above the specimen. Take note of which way you must turn the knob to move the objective lens away from the specimen.

People in science Matthias Schleiden (1804–1881) German botanist Matthias Schleiden, working with Theodor Schwann, proposed the basis of modern cell theory. Schleiden practised law before developing his hobby of botany into a full-time job. Schleiden studied the structure of plants using a microscope. Through these observations he noticed that the different parts of the plant were composed of cells or came from cells. He also recognised that the cell nucleus is important in cell division. Schleiden was one of the first German biologists to accept Darwin’s theory of evolution.

5 Look through the eyepiece and further adjust the mirror to obtain an adequate amount of light through the specimen. Turn the coarse focusing knob so the objective lens moves away from the specimen (remember the direction to turn from step 4) until you obtain as clear an image as possible. 6 Try to improve the sharpness of the image by turning the fine focusing knob. To obtain higher magnification, swap the eyepiece with another one or rotate an objective lens of higher magnification into place. Then repeat steps 4 to 6. The total magnification is obtained by multiplying the magnification of the eyepiece by the magnification of the objective lens being used. For example, if the eyepiece is labelled ‘x 10’, and the objective lens is labelled ‘x 20’, then the total magnification is ‘x 200’.

UNIT

4 .1

Fig 4.1.6

Human cheek cells magnified 100 times

Fig 4.1.7

A sketch of the cheek cells shown in figure 4.1.6

description. An actual view of material taken from the inside of a human cheek is shown in Figure 4.1.6 with a sketch of its main features in Figure 4.1.7. An ant, magnified 125 times

Fig 4.1.5

The electron microscope Prac 1 p. 93

Prac 2 p. 93

Sketching microscope images The area that can be seen through the eyepiece of a microscope is called the field of view. Rather than attempt an exact copy of the field of view, it is a good idea to do a simplified drawing of one or more objects within it. Don’t worry too much about shading—concentrate on the main lines and features. It is essential to record the magnification used for each image and good practice to add a brief written

The transmission electron microscope (TEM) was invented in 1930 by Ernst Ruska and made commercially in 1938 to aid in the study of metals. Instead of using light, this type of microscope uses a beam of tiny negatively charged particles called electrons that are transmitted through a thinly sliced specimen. An image is then produced and projected onto a screen for viewing. When it was found that the beam of electrons did not destroy specimens from plants and animals, biologists were able to use the electron microscope to gather more details than ever before. The transmission electron microscope can magnify up to around a million times, so it can reveal the delicate internal structure of cells and other specimens.

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The microscope

How a scanning electron microscope works magnetic deflectors (condensing lenses) focus the electron beam (like glass lenses focus light)

Fig 4.1.10

electron 'gun'

scan coils move the electron beam across the surface of the specimen

computer

display screen

objective lens

black and white image

specimen placed here

computer used to colourise images

detector and amplifier— electron impacts converted to electrical signal and sent to a display screen

Fig 4.1.8

A transmission electron microscope or TEM

TEM image of Giardia protozoa, a nasty bacterium found in contaminated water and guaranteed to make you ill (magnified x 1200)

Fig 4.1.9

A more recent development is the scanning electron microscope, or SEM, which moves a beam of electrons across the surface of the specimen and reconstructs an image, showing surface detail.

90

Although first invented in 1942, the SEM did not become available commercially until 1965 due to problems with the electron beam. Specimens viewed with an SEM require less preparation but the images are not as detailed. Compare the images displayed in Figures 4.1.9 and 4.1.12. Many of the impressive ‘super-magnified’ images seen in science magazines are obtained using an SEM. Although an SEM produces only black and white images (Figure 4.1.11), a computer may be used to add colour and so make more features distinguishable. Colour SEM pictures obtained this way are called ‘false colour’ images (Figure 4.1.12).

Fig 4.1.11

A scanning electron microscope image of a knotted human hair

UNIT

4 .1 People in science Antoni van Leeuwenhoek

SEM image of Giardia in a human intestine (x 1100)

UNIT

4 .1

Fig 4.1.12

[ Questions ]

In 1674, Dutch amateur scientist Antoni van Leeuwenhoek began writing articles describing amazing discoveries made with simple, hand-held, single-lens microscopes able to magnify from 50 to 100 times (compare this with the 40 to 50 times magnification of other compound microscopes that were common at that time). Leeuwenhoek made the first drawings of single-celled animals, bacteria, sperm cells (which he called ‘animalcules’) and red blood cells. His success was due to the quality of the single lenses he used. These produced much clearer images than those from compound microscopes that used multiple lenses of poorer quality and whose images were often blurred or had colour distortions.

Checkpoint The light microscope 1 Define the following: a microscope b microscopic 2 Produce a diagram showing the main parts of a microscope. 3 Identify another name for the eyepiece. 4 Identify who invented the microscope and in what year was it invented.

Using the microscope 5 Summarise the six steps for using a microscope by drawing a series of cartoons for its use. 6 Produce two rules concerning the safe handling of microscopes.

Fig 4.1.13

A Leeuwenhoek single-lens microscope

The electron microscope 7 Explain what electron microscopes were originally used for. 8 Explain how the electron beam travels in an electron microscope to produce an image. 9 State what SEM stands for.

Think 10 Name two types of compound light microscope. Identify which of the microscopes would give a finer, more detailed image of the specimen.

11 State the total magnification of the following microscopes. a The eyepiece has a magnification of x 20 and the objective lens is labelled x 40. b Both the objective lens and the eyepiece have x 10 on them. c The objective lens magnifies 100 times and the >> eyepiece magnifies 5 times.

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The microscope

12 State the approximate maximum magnification of: a a light microscope b an electron microscope

15 A specimen is 0.2 mm long. Calculate how long it appears if it is magnified by 1000 times. 16 Construct a timeline of the history of the microscope using information from Unit 4.1.

Skills 13 An image of a specimen obtained using a magnification of x 50 is shown below. Accurately sketch the image that would be obtained with a magnification of x 200. Fig 4.1.14

Analyse 17 Explain some advantages of the SEM over a transmission electron microscope. 18 Compare an SEM and a light microscope by listing their similarities and differences in a table.

[ Extension] Investigate 1 Create a poster to teach other students how to use the microscope. ×50

14 Sketch the following microscope specimens using the correct drawing technique.

2 Research some other key people involved in the use and development of early microscopes, and give a brief presentation about their achievements. Choose from the following people: Galileo Galilei, Antoni van Leeuwenhoek, Giovanni Amici, Robert Brown, Matthias Schleiden and Theodor Schwann. 3 A micrometer is an instrument that measures extremely small objects. Describe how it is used. 4 Millimetre and micrometre are units often used when measuring small lengths. Identify what their symbols are.

a

5 Describe how specimens are prepared for viewing by an electron microscope. Present your findings in a flow chart.

Action Fig 4.1.15

Onion cells

b

6 Construct a simple microscope that will allow you to view an object close up. You will find instructions on the Science Focus 1 Companion Website.

Surf 7 Find out more about light and electron microscopes by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4, and clicking on the destinations button.

Fig 4.1.16

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Muscle cells

UNIT

4 .1

[ Practical activities ] Focus on the news Aim To make a wet mount and view it using a

Prac 1 Unit 4.1

UNIT

4 .1

light microscope

Prac 2 Unit 4.1

Equipment

Microscope, microscope lamp, a section of newspaper containing small print, eye dropper, glass microscope slide, cover slip

Method 1 Cut out a small section of newspaper filled with small print. 2 Prepare a wet mount containing the newsprint using the procedure described on page 88 and set the microscope to the lowest magnification.

Observing everyday objects using a microscope Aim To observe common objects at various magnifications

Equipment Microscope, microscope lamp, glass microscope slides, cover slips, eye dropper, small samples suitable for viewing under a microscope, such as a sugar crystal (both plain and caster), salt, copper sulfate, hair, clothing fibres, leaf, insect, writing sample (in ballpoint pen ink), mini grid (optional)

Method

3 Obtain a focused image of the newsprint. Sketch what you see. Record the magnification used. Count how many letters fit in the field of view.

1 Observe a small specimen of each item under a microscope using the steps described on page 88. Specimens may not require wet mount preparation.

4 Slowly move the slide containing the newsprint to the left, and note which way the image appears to move. Then note how the image moves when the slide is moved right, away from and towards you.

2 Sketch what you see in each case and record the magnification used to obtain the clearest image.

5 Repeat steps 3 and 4 but with a higher magnification.

3 If you do not see an image, try shining the microscope lamp onto the surface of the object. Notice that this works very well with solid objects.

Questions

Questions

1 State how many letters fitted into the field of view at each magnification.

1 Describe in words how each specimen appeared.

2 Compare the movement of the image to that of the actual specimen.

2 Explain any observations that you did not expect. 3 Describe two ways in which a microscope could be used to solve crimes.

People in science Robert Hooke (1635–1703) Robert Hooke worked in many fields and was one of the greatest experimental scientists of the seventeenth century. Born in 1635, Hooke was educated at Westminster school and won a place at Oxford in 1653. In 1655 he was employed by Robert Boyle to construct an air pump. Five years later, Hooke discovered the law of elasticity, known as Hooke’s law. In 1665 he published a book, entitled Micrographia (meaning ‘small drawings’), in which he first used the word ‘cell’ to name the microscopic cavities in cork. Hooke developed several techniques for improving the quality of compound microscopes. He was the first to state in general that all matter expands when heated, and that air is made up of particles separated from each other by large distances.

Hooke also achieved fame as chief assistant to Christopher Wren, helping to rebuild London after the Great Fire of 1666. Robert Hooke’s other significant achievement was in the field of astronomy. He constructed one of the first Gregorian reflecting telescopes and was first to suggest that the planet Jupiter rotated on its axis. He made extremely detailed sketches of Mars which were used 200 years later to investigate its rotation. In 1678 Hooke stated a law to describe how the planets moved, a law that Isaac Newton later used in modified form. Hooke thought that he was not given enough credit for the law and became involved in a bitter disagreement with Newton.

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UNIT

context

4. 2 In 1663, the English scientist Robert Hooke discovered cells in cork. This is a special bark that is often used to stopper wine bottles and is similar to, but thicker than, the paper-like bark that you often find on trees in the park or school grounds.

Discovering cells

Cells may be thought of as the building blocks of life, and come in an amazing variety of types and sizes. Skin, muscles, blood and plants are all made up of different types of cells. Most cells are so small that hundreds would fit on a full stop. Our bodies contain over a hundred million, million cells. An example of a very large cell is a hen’s egg. A hen’s egg—a really big cell!

Fig 4.2.2

Using an early microscope, Hooke studied many different objects including feathers, the stinger of a bee and the foot of a fly. When he placed a thin strip of cork under his microscope he saw empty box-like shapes that he thought looked like the small rooms, or cells, occupied by monks of the time. It was logical then to call these box-like shapes cells too. It was not until nearly 200 years later, in 1839, that German biologists Theodor Schwann and Matthias Schleiden proposed the cell theory of life. This theory states: 1 All living things, or organisms, are made up of cells. 2 New cells are created by old cells dividing in two. 3 All cells are similar to each other, but not identical.

Hooke’s first sketch showing ‘cells’ in cork

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Fig 4.2.1

The simplest type of cell is a bacterial cell. Bacteria (sometimes called germs) are tiny cells that can have either good or bad effects. There are different types of bacteria that help us digest food, break down dead plants and animals in soil, and cause disease.

Robert Brown again Robert Brown, in 1831, was the first biologist to observe the cell nucleus and discover that it was in all plant cells. This is the same Robert Brown mentioned in Chapter 2 who used the microscope to discover Brownian motion.

Three different types of bacteria

UNIT

4 .2 Fig 4.2.3 cell membrane cocci vacuole cell nucleus cytoplasm

mitochondrion (not normally visible)

bacilli

Fig 4.2.5

Animal cells

spirilla

cytoplasm

flagellum

cell membrane cell wall

Fig 4.2.4

A diagram of an animal cell showing the main organelles

A diagram of a bacterium showing its main features

There are two main types of cells—animal and plant cells. Each cell is made up of parts called organelles. Each organelle does a separate job inside the cell.

Cells from animals such as humans, pigs or frogs have several Cells from cells? organelles in common. Until 1855 it was 1 Cell membrane—this is a thought that cells could thin, flexible outer layer that appear spontaneously from anywhere. Then encases the cell and controls a German physician, what goes in or comes out. Rudolph Virchow, found 2 Cytoplasm—this jelly-like that living cells can liquid fills most of the cell only come from other living cells through and contains hundreds of reproduction. different chemicals. New substances are made and energy is released and stored here. Think of the cytoplasm as the chemical factory of the cell. 3 Vacuoles—these are storage areas that may contain air, water, wastes and food particles. Animal cells often contain several small vacuoles. 4 Cell nucleus—this is the ‘control room’ of the cell containing the genes composed of DNA. Each gene contains the information responsible for the production of chemicals. These chemicals control chemical reactions in a cell, and how the cell develops and functions. The genes contain instructions in chemical codes for building new cells. 5 Mitochondria—these small objects may be thought of as energy capsules. Each mitochondrion uses sugar and oxygen in a series of chemical reactions to release energy. Mitochondria are so small that they cannot usually be seen using a light microscope. Mitochondria were first described in muscle cells by Rudolph von Kolliker, a Swiss anatomist and physiologist, in 1857.

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Plant and animal cells

a green chemical, chlorophyll, which traps the light energy plants need for photosynthesis. The cell wall contains a tough fibrous material called cellulose and provides the support needed by the plant cell. Plant cells contain a single large vacuole filled with cell sap. Worksheet 4.1 Cell diagrams Prac 1 p. 98

Fig 4.2.8

Fig 4.2.6

Plant cells

Stained human cheek cells

Plant cells As stated in the cell theory, all cells are similar but not identical. Plant cells have several features in common with animal cells, but there are also some differences. Unlike animals, plants need to make their own food with the help of sunlight, carbon dioxide and water. They do this in a process known as photosynthesis. Photosynthesis occurs in organelles called chloroplasts inside leaf cells. Chloroplasts may be seen using a light microscope. Chloroplasts contain A plant cell showing the main organelles

cell wall chloroplast

cell nucleus

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cell membrane

Fig 4.2.7 large vacuole containing cell sap

mitochondrion

People in science Theodor Schwann (1810–1882) Theodor Schwann was a German physiologist who said that the cell was the basic unit of an animal’s structure. In 1836, while investigating digestion, he isolated a substance responsible for digestion in the stomach and named it pepsin. He also observed the formation of yeast spores and said that the fermentation of sugar and starch was the result of yeast reproduction. In 1839 Schwann extended Matthias Schleiden’s work on plant cells to include animal cells. Together they proposed the cell theory of life. Schwann was the first to use the term ‘metabolism’ for the chemical changes that take place in living tissue. Schwann also observed that an egg is a single cell that eventually develops into a complete organism.

UNIT

4 .2

UNIT

4 .2 [ Questions ]

Checkpoint Discovering cells 1 Identify who first used the term ‘cell’ to describe the small structures in a slice of cork. 2 State when Schwann and Schleiden proposed the cell theory. 3 Write three points to briefly describe the cell theory. 4 Identify the simplest type of cell.

17 The digestive systems of sheep, cows and rabbits contain special bacteria which help break down a substance found in cell walls that humans are unable to break down. State which substance this might be.

Analyse 18 Construct a table like the one shown here to compare animal and plant cells. Make sure you include some similarities and some differences.

Animal cells 5 Identify the part of a cell that could be called: a the ‘control room’ b the ‘chemical factory’ c the ‘gatekeeper’ d the ‘powerhouse’ e the ‘walls’ 6 Identify three types of body cells.

Plant cells 7 Identify the green substance in plant cells and state its function. 8 Clarify the following terms related to plant cells: a photosynthesis b cell wall c cellulose 9 Identify three differences between plant and animal cells.

Think

Feature

Animal cell

Plant cell

19 Plant cells need to have thicker walls than animal cells. Explain why. 20 Explain why there are fewer types of plant cells than animal cells.

[ Extension] Create 1 Construct a 2D or 3D model of a plant or animal cell using any materials you can find.

10 Compare an organelle in a cell to an organ in the human body. How similar are they in what they do?

Investigate

11 Clarify the term ‘organism’.

2 Investigate the dates of key discoveries relating to the microscope and cells. Include those covered in this chapter and others that you research. Draw a time line using this information.

12 Identify how big cells are. 13 State how many cells our bodies are thought to contain. 14 Draw a diagram of an animal cell and a plant cell side by side. Compare the cells by labelling the parts that are common to both with one label. 15 Muscle cells contain large numbers of mitochondria. Explain this observation. 16 Identify the contents of a vacuole if it is in a: a plant cell b animal cell

Surf 3 The confocal microscope is currently being developed by an Australian company. Investigate this new type of microscope and how it may be used to observe skin cells without the removal of skin from the body. Make your investigation easier by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4, and clicking on the destinations button.

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Plant and animal cells

UNIT

4 .2

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[ Practical activity ] Onion and banana cells Aim To observe and draw plant cells

Prac 1 Unit 4.2

Equipment A microscope, potassium iodide stain, lamp, filter paper, glass microscope slide, eye dropper, water, cover slip, onion skin, banana sample, wooden spatula (an icy pole stick is ideal)

Extension: rhubarb Method 1 Obtain a thin (one cell thick) layer of onion skin. Your teacher will show you how to do this. 2 Place a small sample of the onion skin onto a glass microscope slide.

Extension 1 Try to obtain a view of rhubarb cells by first peeling some of the outer layer from a piece of rhubarb.

Questions 1 Explain why stain was recommended when viewing banana cells, but not for onion cells. 2 Identify which cells were easier to observe. 3 Describe some of the similarities and differences you observed between banana and onion cells. 4 If you were able to see rhubarb cells, describe them.

3 Place a drop of water on the sample.

onion skin

4 Carefully place a cover slip on top of the onion skin and water. 5 Observe at two different magnifications using the microscope. 6 Draw your field of view at the two different magnifications. 7 Smear a thin layer of banana onto a clean glass microscope slide. 8 Place a drop of iodine stain on the sample. 9 Carefully place a cover slip on top of the banana and stain. 10 Obtain a clear image using the microscope and draw what you see.

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drop of water

Fig 4.2.9

Lowering the cover slip

UNIT

context

4.3 The first cells on Earth were very similar to the simplest cells we find on Earth today, called bacteria. Bacteria have only one cell each. Each bacterial cell does everything needed to keep the bacterium alive. In more complicated organisms, cells live together in groups or colonies. In these colonies the cells are specialised. Specialised cells in colonies do particular jobs which could not be done by single cells living alone. Some cells, for example, specialise in swimming and others in feeding. The larger a plant or animal is, the more specialised cells it contains. The human body is made up of billions of cells, of which there are about 200 different, specialised types.

red blood cell

nerve cell involuntary muscle cells

bone cell

Different types of human cells Just as all the parts of a car work together to keep it going, the 200 different types of specialised cells inside us work together too. Animals and plants that are made up of lots of cells working together are called multicellular, meaning ‘many cells’. The human body must carry out several different jobs or functions, and requires many different types of cells to do so. Having different types of cells makes doing these jobs more efficient, as cells can focus on one main thing at a time. Blood cells carry food and oxygen around the body, muscle cells assist movement, nerve cells ‘Look at the wee-beasties’ send messages from the brain to the muscles, skin cells cover our bodies and keep out infection, bone cells help support the body and protect the internal organs, fat cells insulate the body and store energy, while sperm and eggs cells can combine to produce a new human being.

Leeuwenhoek discovered many types of cells. He was the first to see single-celled, living organisms in 1674. Imagine his excitement when he looked through his microscope and saw protozoa moving around! Then in 1683 he discovered bacteria, which were even smaller than protozoa!

white blood cell

fat cell

part of a skeletal muscle cell

Various types of human cells, each specialised for a different purpose

Fig 4.3.2

Fig 4.3.1

A coloured SEM image, magnified 3000 times, of red and white blood cells

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Specialised cells SEM image of sperm cells and an egg cell

Fig 4.3.3

When plants take in carbon dioxide they give out oxygen and also lose a little water from their leaves. Special guard cells on the underside of a leaf open and close small openings called stomata to reduce this water loss. Stoma is the term for a single stomata. Water is absorbed from soil by root Prac 1 p. 102 hair cells.

Single-celled organisms While humans contain more than 200 different types of cell, there are some primitive forms of life that are made up of only a single cell. These organisms are called unicellular, meaning ‘one cell’. This cell carries out all the required functions such as food intake and movement.

Plant cells

Plants also contain different types of cells that perform different functions. Several types of specialised plant cell are shown in Figures 4.3.4 to 4.3.8. A layer of cells near the top of a leaf does most of the photosynthesis. Chloroplasts in the cell use energy nucleus from the Sun to convert carbon dioxide and water into glucose. This is then used as food for the chloroplasts plant. Oxygen is made as a waste material. Special conducting cells form tubes or pipes that transport water and nutrients to all parts of the Photosynthetic cell Fig 4.3.4 plant.

Expert survivor The single-celled organism Chlamydomonas can grow a thick wall to survive severe drought, where it may blow around like dust in the wind and ‘reactivate’ when conditions are more favourable.

water conducting tube sieve

food conducting tube

Fig 4.3.5

Conducting cells

cell in root root hair

guard cell

nucleus soil

Fig 4.3.6

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Guard cells around a stoma

Fig 4.3.7

SEM image showing the guard cells around an open stoma

Fig 4.3.8

Root hair cell

Perhaps extraterrestrial life No sex please, includes not little green we’re amoebae! ba reproduces without amoe The people, but different types of a process called binary in sex, unicellular organisms! There fission in which the cell nucleus is currently scientific debate splits in two first, followed by about what appear to be the cytoplasm to produce a copy of the original cell. primitive organisms found in meteorites from Mars. You can usually find unicellular organisms in a drop of pond water viewed under a microscope. Because some single-celled organisms show both plant and animal characteristics, they are often classified not as plants or animals, but as protists. Different types of protist include: 1 flagellates—these have a long, whip-like tail or flagellum that helps them move 2 ciliates—these move due to a wave-like beating of tiny hairs (or cilia)

3 amoebas—these have no definite shape but flow rather than swim 4 sporozoans—these generally don’t move themselves, but exist in other cells. The potentially deadly disease malaria is caused by a sporozoan that lives in blood cells. The disease may be transferred when a mosquito passes on infected blood. Not all unicellular organisms cause disease— many are important parts of the food chain.

UNIT

4.3 Please boil the water For two months in 1998 over 3 million residents of Sydney were asked to boil their drinking water to kill two microscopic protists. The two flagellate protozoans were Cryptosporidium and Giardia, which can cause severe illness when found in large quantities. A TEM and an SEM image of Giardia are shown in Figures 4.1.9 and 4.1.12.

Worksheet 4.2 Single-celled organisms

Fig 4.3.9

Prac 2 p. 102

Single-celled organisms commonly found in pond water gullet flagella

eye spot

pseudopodium cilla

nucleus

cytoplasm

chloroplast

cytoplasm

oral groove

nucleus flagellum

cell wall nucleus

chloroplast Chlamydomonas

UNIT

4 .3

Paramecium

nucleus

cell wall Amoeba

Euglena

[ Questions ]

Checkpoint Different types of human cells 1 State the type of human cells that: a help keep out infection b send messages from brain to muscle c carry oxygen d assist with movement 2 Draw two different types of human cell and state their function. 3 State approximately how many different types of specialised cells there are in the human body.

Plant cells 4 Identify four types of specialised plant cells. 5 Describe what would happen to a plant without guard cells. 6 The cells on a leaf that specialise in photosynthesis are found only on the upper surface. Explain why.

Single-celled organisms 7 State another name for a single-celled organism. 8 Identify four types of unicellular organism. 9 Identify a disease caused by a unicellular organism.

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Specialised cells

Think 10 Construct a diagram to explain how an amoeba reproduces. 11 Draw labelled diagrams of two different protists to clarify their structures.

17 Two types of conducting cells form vessels that are grouped together in a plant. Explain why this is a good idea. 18 One type of protist has something in common with plants. Identify which protist it is and what it has in common.

12 Describe a flagellum. 13 Identify which type of protist moves by beating many hair-like structures.

[ Extension]

Analyse 14 Identify the first single-celled organisms.

Investigate

15 Explain how the functions that cells performed changed when they began to form colonies.

1 Many diseases are caused by protozoa, including malaria. Construct a brochure to be placed in a doctor’s clinic to teach others about malaria. Your information should include: a the cause of the disease b the signs and symptoms of the disease c who is most likely to get the disease d methods to prevent infection e possible cures or treatments.

16 There are benefits and disadvantages in having specialised cells doing different jobs. a List some advantages and disadvantages of having specialised cells. b List some advantages and disadvantages of having one cell doing all jobs in a living thing. c Evaluate whether it is better to be a single-celled organism or to be made up of lots of specialised cells.

UNIT

4 .3 Prac 1 Unit 4.3

[ Practical activities] Viewing prepared slides

Life in a drop of water

Aim To observe prepared microscope slides of specialised plant and animal cells

Aim To observe and draw single-celled organisms in pond water

Equipment

Prepared slides of various specialised plant and animal cells, microscope, lamp

Method 1 Observe a prepared slide using a microscope. 2 Sketch the image and label your sketch. Include the name from the slide and the magnification used. 3 Repeat with several different slides of plant and animal cells.

Equipment Some pond water, or other water containing single-celled organisms (e.g. a hay infusion), microscope, lamp, glass microscope slide, cover slip, eye dropper

Method 1 Place a drop of pond water onto the glass microscope slide and cover it with a cover slip. 2 Use a microscope to obtain a view of the life within the drop of water.

Questions

3 Sketch as many different organisms as you can.

1 Compare the slides, looking for any similarities and differences.

Questions

2 Explain the advantages of using prepared slides rather than obtaining your own specimens. 3 Describe the features within the cells that you were able to observe.

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Prac 2 Unit 4.3

1 State how many different organisms you saw. 2 Explain how they appeared to move. 3 If possible, identify and name each type of organism.

UNIT

context

4. 4 People in a group can perform more complex tasks than one person alone. Like people, the different specialised cells in our bodies are organised into groups to help them work more effectively.

heart muscle cell

Cells, tissues and organs A human being develops from a single fertilised cell called a zygote, formed by the combination of a male Siamese twins sperm cell and a female egg When a fertilised egg cell cell (see Figure 4.3.3). This does not completely split cell then divides to form two during the early stages of new cells. The two new cell division, Siamese twins may result. Below is a cells then divide to form picture of a two-headed four cells and so on and so snake formed this way. on, until millions of cells are present. Eventually some cells begin to develop differently, and begin to do different, specialised jobs. Groups of similar cells are called tissue. Tissues in turn may be grouped together to form an organ. For example, heart cells form heart tissue, which makes up the heart, the organ specialised for pumping Super cells yet not have that blood around the human cells yonic Embr become specialised have the body. Skin cells form ability to develop into almost any skin tissue that makes type of human tissue. These cells stem Mice . up another organ—the cells stem called are cells have successfully been skin. Some other human injected into damaged spinal organs made from regions of mice and have resulted specialist tissue and in the growth of new cells to cells are the brain, repair the damage. It is thought that human stem cells have the intestines, liver, potential to rebuild nerves and kidneys and eyes. repair spinal cord injuries, as well ses disea e Animals and plants as treat degenerativ such as Alzheimer’s disease and may contain several Parkinson’s disease. different organs.

heart (organ) heart tissue

A cell, a tissue and an organ

Fig 4.4.2

Fig 4.4.1

Failure of cells to divide properly during early development led to this ‘Siamese snake’.

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Groups of cells

History of science Cloning cells One of the great moments in the history of science was the cloning of Dolly the sheep. Professor Ian Wilmut and his team were the first to clone an animal from the cell of another adult animal. This took place at Roslin Institute, near Edinburgh in Scotland, during 1997 after many years of research. Dolly was made using a body cell taken from the udder of another sheep. Cloning is the process of creating a copy of an organism by placing the contents of a cell from the original animal into a donor cell which is then implanted in a ‘surrogate mother’ and allowed to develop into a complete animal. Dolly’s birth sparked a debate about the ethics of cloning and a rush by other scientists to copy the method used to clone her. Dolly was later diagnosed with a number of diseases including arthritis, and was put down when six years old after it was found she had developed a deadly lung disease. Sheep like Dolly normally live to 11 or 12 years and critics of cloning have warned that her early

death is proof of the dangers of attempts to clone humans. After a post-mortem examination, Dolly was stuffed and put on public display at a Scottish museum. It is possible that particular animals such as pigs may be cloned. The advantage here is that their hearts might be suitable for transplant into humans suffering from terminal heart disease. There are, however, many ethical and religious concerns with cloning. In many cases the law is yet to catch up and rule on these concerns. Although a great moment in science, cloning has led to many new developments and is now just a link in the chain of scientific discovery and human development.

donor nucleus reprograms cell stem cell from donor sheep embryo

donor nucleus injected into egg

implant in surrogate

clone

unfertilised sheep egg

Fig 4.4.3

remove DNA

How cloning works

The most famous cloned animal —Dolly the sheep

Fig 4.4.4

Worksheet 4.3 The history of cloning

Systems A group of organs that work together is called a system. For example, in humans and animals, groups of muscles work together to form the muscular system. Some other human body systems are described briefly here and will be studied in more detail later in this series.

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Several systems together form an organism, or living thing, such as a human. In humans, the nervous system includes the brain, spinal cord and nerves. The brain and spinal cord are referred to as the central nervous system; they send and receive messages which are carried by the nerves as a series of electrical signals and chemical changes.

UNIT

4.4 Lung Heart

female

male

Fig 4.4.5

The nervous system

Fig 4.4.6

The circulatory system

The circulatory system comprises the heart and blood vessels that carry food and oxygen to cells. Waste materials in the blood are transported to other organs for separation before being removed from the body. The digestive system includes the stomach and intestines and breaks down food into substances small enough to be absorbed into the bloodstream. Some separation of waste materials also occurs here. The reproductive system produces sex cells and contains the organs required for sexual reproduction. In a woman, this includes the uterus (sometimes called the womb), where a baby develops. The respiratory system includes the trachea (or windpipe), lungs and diaphragm. The respiratory system is where oxygen is transferred to the blood for circulation to other parts of the body. Carbon dioxide is expelled from the lungs when we breathe out. Excretion is the removal of waste from the body. The lungs expel carbon dioxide and the skin excretes sweat, but the main body system involved in excretion is the urinary system. Here, the kidneys filter out wastes from the blood and control the amount and contents of body fluids, producing urine in the process.

Fig 4.4.7

The digestive system

Fig 4.4.8

Fig 4.4.9

The respiratory system

Fig 4.4.10

The reproductive system

The urinary system

The skeletal and muscular systems work together to provide protection, movement and support for the body. Worksheet 4.4 The human skeleton

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Groups of cells

Plant systems skull (cranium)

jawbone (mandible) neck vertebrae

frontal muscle temporal muscle chewing muscle (masseter) neck muscles

collar bone (clavicle) shoulder muscles (pectorals)

shoulder blade (scapula) rib cage back (lumbar) vertebrae

lower arm muscle (brachioradialis) main forearm bone (ulna)

abdominal muscle (rectus abdominis)

small forearm bone (radius) hip bone (pelvis) wrist bones (carpels) thigh bone (femur) kneecap (patella) small shin bone (fibula)

thigh muscle (sartorius)

Plants are also made of cells which group together to form organs and systems. Leaf cells group to form a leaf, which is an organ of the plant. Several leaves form a food-making system for the plant. Other plant systems may include: • a reproductive system consisting of the parts of a flower • a food and water transport system consisting of a network of veins • a food storage system in the form of a bulb • a root system for securing the plant in the ground and obtaining water and nutrients from the soil. These plant systems are studied in more detail later in this series.

calf muscle (gastrocnemius)

main shin bone (tibia)

3 State the names of four different organs.

Systems

foot bones (tarsals)

4 Describe what is meant by the term ‘body system’. The major parts of the skeletal and muscular systems

UNIT

4.4

5 Copy and complete the table below to summarise the six body systems.

[ Questions ] Body system

Checkpoint Cells, tissues and organs 1 Clarify what the word ‘zygote’ means. 2 Copy and complete, using the words tissue, organ and cells (one word is used twice): Many ______ form ______. Groups of ______ make up an ______.

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Fig 4.4.11

List of its parts

Brief description of what it does

Fig 4.4.12

Think 6 If a cell is represented by a circle (shown in diagram A), select the diagram (from B, C, D or E) that best represents: a tissue b an organ c a body system

A

B

C

D

UNIT

4.4

E

Note that each answer is different. 7 Identify which body system is the main one involved in each of the following situations. a Your face goes red after you run for a kilometre. b Your leg moves up after you are tapped on the knee. c You need to go to the toilet. d You feel ‘full’ after a meal. e You gasp for air after swimming under water. 8 Look at each body system on page 105 and name at least one organ in each system.

Fig 4.4.13

9 Where in the human skeleton would you expect to an example of each of the joints shown above? 10 Study the plant diagram in Figure 4.4.16 and state which part contains each of the following systems. a reproductive system b food-making system Fig 4.4.16

Pivot joint

Fig 4.4.14

Hinge joint

Fig 4.4.15

Ball and socket joint

c food and water transport system d water absorption and anchoring system e food storage system 11 Describe what you think the term ‘locomotion system in humans’ means.

[ Extension] Investigate 1 Investigate the endocrine system and produce a small chart showing the main glands of the endocrine system and their function.

flower leaf

bulb roots

Surf 2 Find out more about body systems by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4, and clicking on the destinations button. Choose a body system and examine in more detail how it works. Produce a PowerPoint presentation or poster to show your findings.

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Science focus: Stem cells Prescribed Focus Area: Current issues in research and development Many scientists are now researching special types of cells called stem cells. Stem cells are very important and have the potential to cure many diseases. However, there are also many issues to consider when using stem cells. Stem cell research has created concern for some in the community because the best source of stem cells is a growing human embryo. The dilemma is that the growing embryo is the earliest stage of a human life— extracting the stem cells destroys the embryo and so a potential life is lost. What is a stem cell? A stem cell is a special cell. In the earliest stages of a human life, stem cells can divide to produce all the different specialised cells of the body. After birth, as we grow, the number of stem cells in our bodies decreases. The stem cells left in adults can usually only grow into certain types of cells. Adult stem cells usually only repair injuries to damaged tissues or broken bones, as the adult body has finished growing. The single fertilised egg in no way resembles a human, but contained in the nucleus is all the information on how to build all the different types of specialised cells. These cells make up the tissues and organs that will allow the baby to live and grow. Embryonic stem cells are taken from the inside of the blastocyst.

After 5–7 days the egg grows into a blastocyst

Inner stem cells are collected from blastocyst

Stem cells are placed in growth mediums

Skin cells

Fig SF4.1

Nerve cells

Muscle cells

Stem cells taken from an embryo can be grown into many types of specialised cells.

Researchers think that there is the potential to collect embryonic stem cells and grow them into any form of specialised cell (see Figure SF4.1).

The growth of a human is an amazing process.

Fig SF4.2

Sperm

Egg

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Fertilised egg

Zygote (first cell of new organism)

Blastocyst

Stem cells

Foetus

Human

The future Unfortunately it appears that when born, or shortly after, humans lose the last of the stem cells that are capable of growing into new nerve cells. This is why humans cannot repair damage to the brain or spinal cord. It is because embryonic stem cells can grow into so many different tissues, including nerves, that many scientists and members of the community strongly support further research. Scientists working on mice have already shown that a cut spinal cord can be repaired using embryonic stem cells injected into the ends of the damaged spinal cord. In a human, a damaged spinal cord can result in paraplegia (loss of use of the legs) or, when a broken neck occurs, quadriplegia (loss of use of both the legs and arms). There are currently no successful treatments for these injuries. Stem cells may also have other medical applications such as: • growing new organs for someone who needs a transplant • growing new body parts to replace those lost in an accident • repairing damage to the brain from diseases that cause the brain to slowly stop working, like Parkinson’s disease The process of using stem cells to treat a human condition

• repairing damaged heart muscle after a heart attack • growing new skin for burns victims. Scientists are also researching whether adult stem cells can be used for these purposes, and are having some success. But it is still embryonic stem cells that offer the most potential.

Stem cells are grown in containers such as this.

Fig SF4.4

Fig SF4.3

What’s your opinion? Method 2

Healthy normal cell taken

DNA of cell transferred into an egg

Method 1 Adult stem cells taken Patient

Cell types injected into patient

Stem cells placed in culture

Specific cell types grown

Embryo grown into blastocyst Stem cells placed in culture

The government has said that scientists can use embryos left over from IVF (in vitro fertilisation) for stem cell research in the future. The following comments on the use of embryonic stem cells were made by some well-known Australian scientists. • The Australian Academy of Science’s Professor John White argues that we should use embryonic stem cells, because stem cells that are now being used are not good enough. Professor White argues that while much can be learned from animal experiments, experiments in human cells are needed now. • IVF pioneer and stem cell researcher Professor Alan Trounson of the Monash Institute of Reproduction and Development supports the use of stem cells from ‘spare’ IVF embryos. He thinks Australia should lead the way in this research.

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• Sir Gustav Nossal supports the need for (more) animal research. He said there is ‘a huge amount of learning to be done’ in mouse experiments before embryonic stem cells can be used in humans. He expects it will take at least 10 to 15 years before embryonic stem-cell therapies become available. • Dr McCullagh, formerly of the Australian National University, is a specialist in transplantation and foetal development. He believes we should find ways to use the stem cells that are already in our bodies. Dr McCullagh said that he does not agree with destroying human embryos for research.

Sir Gustav Nossal, medical researcher

Fig SF4.5

[ Student activities ] 1 a Use the Internet and newspapers to gather reports on some experiments being carried out with stem cells. b Use the information collected to outline what is being studied. 2 Create a poster or cartoon strip to explain to people what embryonic stem cell research is about. 3 Investigate the stem cell debate by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4, and clicking on the destinations button. Use the available sites and any other material to answer the following questions. a List the advantages and disadvantages of stem cell research. b Investigate why some in the community are concerned about stem cell research. c Produce a survey to analyse public opinion about stem cell research. Test your survey on your classmates, parents or the community and write a brief summary of your results. d Evaluate the information you have collected and make a decision. Do you support embryonic stem cell research? Give reasons for your answer.

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4 Research has shown that adults may have some remaining stem cells that can be used for research. Despite this there is still strong support for using embryonic stem cells. a Investigate and list the advantages of using embryonic stem cells over adult stem cells. b It might be better for a person who has a particular medical problemto use their own stem cells rather than embryonic stem cells. Do some research to explain this idea. 5 Hold a class debate on the topic: ‘Research into embryonic stem cells can provide enormous benefits and should continue’.

Chapter review [ Summary questions ] 1 What is a compound microscope? 2 State two rules you should remember when using a microscope. 3 List the main parts of the microscope from its top to its base. 4 State the type of material Robert Hooke was looking at when he coined the term ‘cells’. 5 Sketch a bacterium, showing its main parts.

17 Identify two features that plant and animal cells have in common. 18 Copy and complete the following table to summarise the history of cells. Include as many scientists as you can find throughout this chapter.

Date

Scientist

Discovery

1609

Hans Janssen and his son

Invented the compound microscope

6 Sketch an animal cell and label its parts. 7 Sketch a plant cell. Label its parts. 8 Explain the purpose of each of the following cell organelles. a cell membrane b cell wall c cytoplasm d vacuole e cell nucleus f chloroplasts 9 Explain what a specialised cell is. 10 Name three types of human cells and state what job each does. 11 Name two specific protists, and state which type of protist each one is. 12 Identify whether a protist is a multicellular or unicellular organism. 13 Describe two different types of plant cell, and what each does.

[ Thinking questions ] 14 Calculate the overall magnification for a microscope with a 20 x eyepiece and a 50 x objective lens. 15 Explain why it is important to develop different types of microscopes. 16 State the names of two different types of microscopes and explain the benefits of each to society.

[ Interpreting questions ] 19 a Use examples to distinguish between unicellular and multicellular organisms. b List the advantages and disadvantages of an organism being multicellular. c List the advantages and disadvantages of an organism being unicellular. d Evaluate whether unicellular or multicellular organisms have a greater advantage in terms of survival. e Are humans unicellular or multicellular? Explain your answer. 20 Identify which of the words below involves: a the most cells b the least cells tissue, body system, organ 21 Choose two body systems and describe them briefly. Include a simple diagram that shows the main parts of the systems. 22 Re-read the information about Leeuwenhoek on page 91 and assess the value of his discoveries. Give reasons to support your answer. Worksheet 4.5 Cells crossword Worksheet 4.6 Sci-words

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Heat, light and sound Key focus area:

4.3, 4.6.1, 4.6.4, 4.6.5, 4.6.6

Outcomes

>>> The applications and uses of science By the end of this chapter you should be able to: identify different forms of energy and objects that have energy use models to describe different forms of energy describe how energy is changed from one type to another describe sound and light as different forms of energy identify how heat is lost and gained and describe how this can be controlled

Pre quiz

identify and describe how the understanding of energy is used in technological development.

1 Give three examples of energy. 2 Why do you feel cold when you jump into a pool that is at the same temperature as the surrounding air?

3 How does a thermos keep your soup hot all day long?

4 Describe three devices that use energy.

5 Draw a diagram to show how a periscope works.

6 When is a sound dangerous?

5

UNIT

context

5.1 On 16 July 1945, scientists exploded the first atom bomb. For the first time the atom was split in a nuclear reaction that released a huge amount of energy very quickly. This enormous explosion was seen 400 kilometres away, and the shock wave was felt 80 kilometres away.

What is energy? Playing football or netball or climbing a mountain requires hard work and uses of a lot of energy. We can simply say that energy is the ability to do work. There are two main types of energy: potential energy and kinetic energy. But these can take many different forms. Potential energy is stored energy. The energy in food, a stretched rubber band, petrol or a battery is stored inside the material. Anything that is held above Jack in the box—the potential energy of the compressed spring is changed into kinetic energy as the box is opened.

Fig 5.1.1

The energy released was made up of different forms including heat, light and sound. This single event changed our lives forever. So what is this thing called energy? the ground has potential energy because gravity is trying to pull it down. When we release stored or potential energy it is often changed into kinetic energy. Kinetic energy is energy of motion. All moving things have kinetic energy. We are using kinetic energy every lunchtime when we play handball, train for netball or just sit around talking. All energy is measured with the same unit. This unit is called the joule and has the symbol ‘J’. The symbol is commonly seen on food packaging where the units are in kJ, which represents kilojoules or 1000 joules.

Forms of energy Potential and kinetic energy can exist in many different forms, as shown in Figure 5.1.2.

People in science James Joule (1818–1889) James Joule was a British physicist who found that rather than energy being lost or destroyed, various forms of energy are changed from one form to another. This is the law of conservation of energy. Joule was born in Manchester in 1818 to a wealthy brewery owner. From 1834 to 1837 the chemist, John Dalton, taught him privately at home. In 1838 he began experimenting in a laboratory equipped at his own expense at the brewery. In 1843 he determined the amount of work required to produce a unit of heat, now known as the Joule. In 1852 Joule, along with William Thomson, discovered that when a gas expanded, the temperature fell. This effect was later used to make refrigerators. In 1875 Joule’s money ran out and he died in 1889 after a long illness.

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Energy

a. Electrical

b. Gravitational

c. Elastic

d. Nuclear

e. Light

f. Heat

g. Chemical

h. Sound

i. Kinetic Forms of energy

Fig 5.1.2

Energy transformations Energy can be changed or transformed from one kind of energy to another. Most machines and appliances operate because they are able to change energy into another type, and then use this energy to do work. Some examples of energy changes or transformations are shown in Figure 5.1.3. The lighting of a match is one example of an action that involves many energy changes. First, moving our hand to strike the match involves kinetic energy. This is turned into heat and sound energy caused by the friction of the moving match head against the side of the box. The heat energy from the friction causes a chemical reaction to begin. This releases the chemical potential energy stored in the match head and wood as light Prac 1 Prac 2 p. 117 p. 117 and heat energy.

114

Fig 5.1.3

In most everyday actions energy changes from one form to another.

UNIT

5.1 The source of all energy Where did all the energy on Earth come from? In fact all the energy comes from the Sun. Plants capture the Sun’s energy and turn it into chemical potential energy when they grow. Animals eat the plants and use this energy for many purposes. The energy absorbed by plants eventually ends up in many other places such as in the petrol we use for transport, and the wood we use for making paper. This energy can then be released once more when these materials are burnt in a car engine or a fire. Sunlight is absorbed by non-living objects such as rocks and later released as heat. Of course without the Sun’s light energy we would always be in the dark. Solar cells can turn the Sun’s light energy directly into electricity. Energy transformations are all around us and can all be traced back to the Sun.

Electrical energy 200 J

50 J Light energy

100 J Motion Electrical energy 1000 J

UNIT

5.1

[ Questions ]

Checkpoint What is energy? 1 Clarify what is meant by the term ‘energy’. 2 Identify the two main types of energy. 3 Explain the two types of energy in your answer to question 2, giving an example of each.

Forms of energy 4 List all the forms of energy shown in Figure 5.1.2. 5 Identify an example of each energy form you have listed.

Energy transformations 6 Clarify what is meant by the term ‘energy transformation’. 7 Construct a flow chart to summarise the energy changes when a match is lit.

100 J Sound 200 J Light 600 J Heat

Energy conservation For all energy there is a chain of energy changes, like the process we described for the match. In fact, energy can never be created or destroyed. It can only be changed from one form to another. This is the law of conservation of energy. Sometimes it appears that energy is lost, but when you look closer you find that the energy has ‘gone’ into other forms, such as sound, heat or light. Some energy changes are shown in Figure 5.1.4.

Heat energy 150 J

Energy changes for a light globe and a toaster

Fig 5.1.4

Worksheet 5.1 Energy changes

The source of all energy 8 Identify what is said to be the source of all energy on Earth. 9 Identify an example of how humans use the Sun’s energy directly. 10 A herbivorous animal eats only plants. Give an example of this type of animal and explain how it gets energy from the Sun through its food. 11 Carnivorous animals only eat other animals or insects and do not eat plants directly. Give an example of a carnivorous animal and explain how their energy also can be traced back to the Sun.

Energy conservation 12 State the law of conservation of energy. 13 Clarify what we really mean when we say that energy is ‘lost’. 14 We burn petrol in a car engine to get the car moving. A lot of energy, however, is wasted. Identify two forms of energy into which this ‘lost’ energy is converted.

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Energy

Think 15 Describe the energy transformations that take place when an atomic bomb explodes. 16 Describe the energy transformations that take place in the following situations. Remember, the energy may be transformed more than once, and to more than one type or form of energy. a toaster b light globe c Discman d car engine e a person parachuting out of an aeroplane f a person doing a bungee jump g a student riding a bicycle, starting from rest 17 Solar panels capture the Sun’s energy and turn it into electricity. Explain why solar panels are similar to plants.

Analyse 18 For each of the energy transformations listed in the table, identify which situation it belongs to. 19 The following energy transformations occur in a hydro power station. Study each stage of the process and answer the questions that follow.

a Not all the energy that is stored in the water at the start is turned into electricity at the end. Some people could say that energy is ‘lost’ in each stage of making electricity. Explain where this lost energy may go at each stage of the process above. b Identify a better term to replace the word ‘lost’. c Describe the energy changes that could occur as a person at home turns on the television and uses the electrical energy.

Create 20 Construct a model of a simple device that transforms energy from one type to another. Present your model to the class and explain the energy transformations involved.

Energy transformation

Situation

a

Chemical potential → heat and light

Jack in the box

b

Light → heat

Torch

c

Chemical potential → electrical → light and heat

Cup falling off the bench

d

Chemical potential → kinetic and heat

Car braking

e

Gravitational potential → kinetic → sound (and heat)

Person running

f

Chemical potential → kinetic → gravitational potential

Solar hot water heater

g

Elastic potential → kinetic

Crane lifting an old car

h

Kinetic → heat and sound

Burning wood in a fire

Water stored in dam high up in mountains (gravitational potential)

→ Water falls down pipes (kinetic)

→ →

Water turns turbine (kinetic) Turbine produces electricity (electrical)

[ Extension ] Investigate 1 Investigate the energy changes that occur in a coal power station. Draw a flow chart to present your information. 2 Identify 10 devices in your home that transform energy and write down the energy transformations for each.

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Surf Find out more about the following science applications by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5, and clicking on the destinations button. 3 Investigate renewable and non-renewable energy sources that we use to make energy for everyday living. a Construct a table to show the advantages and disadvantages of each energy source. b Evaluate each energy source and decide whether it is suitable to use in the future. Give reasons to support your decisions.

UNIT

5. 1 Prac 1 Unit 5.1

UNIT

5.1 [ Practical activities ] Popcorn

Chemical energy

Aim To use heat energy to change the stored energy in corn into sound and motion

Aim To perform an energy transformation

Equipment Popping corn, small saucepan with lid, Bunsen burner, cooking oil

Method 1 Place a small amount of cooking oil in the saucepan. 2 Cover the bottom of the pan with popping corn.

Prac 2 Unit 5.1

Equipment Test tubes, test tube rack, 100 mL measuring cylinder, sodium hydrogen carbonate (bicarb soda), hydrochloric acid (2 M), acetic acid (vinegar) (2 M)

Method 1 Place a spatula of sodium hydrogen carbonate into a test tube.

3 Heat the saucepan slowly, constantly moving it in the flame.

2 Place the test tube in a test tube rack.

4 Continue heating, noting any changes that occur.

3 Measure 20 mL of the hydrochloric acid in a measuring cylinder. 4 Carefully but quickly pour the acid into the test tube. 5 Observe any energy released during the reaction. There may be more than one type of energy released, so use your senses of sight and hearing to examine the reaction carefully. 6 Repeat steps 1 to 5 using the acetic acid.

Saucepan

Questions 1 Describe the energy transformations that took place in this reaction.

Bunsen burner

2 Describe any difference in the amount of bubbles formed by each acid. 3 Identify the acid that released energy the fastest. Explain how you could tell. Fig 5.1.5

Questions

4 Identify the acid that released the most energy. Explain how you could tell. 5 Identify the acid that had more chemical potential energy stored in it.

1 List the energy changes that occurred during the heating of the corn. 2 Compare the unpopped corn to the popped corn and suggest what happened to the grains.

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UNIT

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context

5. 2 In summer you can feel the Sun’s heat warming you up. You have to take off layers of clothing to stay cool. In winter you increase the amount of clothing you wear to stop the cold air from cooling you down. We also use heat for many purposes such as cooking and drying clothes. Heat is a very common form of energy that affects us every day.

The particles do not actually move along the length of the object; they merely pass along the increased vibrations. Have you ever walked barefoot across a tiled floor and felt that the floor was quite cold, even though it must have been at the same temperature as the rest of the room? Meanwhile the rest of your body didn’t feel cold. The reason is that the tiled floor is a better

Heat and temperature Heat energy can increase the temperature of a substance. Do not confuse heat and temperature— they are not the same thing. Heat is a form of energy, but temperature is not. To understand the difference, consider two Bunsen burners set on a blue flame, one heating a beaker half-filled with water and the other heating a beaker filled with water. After one minute, both beakers have been supplied the same amount of heat energy, but the fully filled beaker will be at a lower temperature. When an object is hot, its particles vibrate more rapidly. Temperature measures how much these particles are vibrating. Heat will move from one area to any other area that is at a lower temperature. Heat moves in three ways—by conduction, convection or radiation. Worksheet 5.2 Other temperature scales

Conduction You may have experienced conduction when washing the dishes or running a bath. Have you ever felt one part of an object (e.g. a plate or metal tray) get hot when another part is held under running hot water, or been burnt by touching a metal tap that has had hot water running from it? These are both examples of conduction. Conduction occurs when the particles in one part of an object vibrate more, and these vibrations are passed on from particle to particle through the object.

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People in science Anders Celsius (1701–1744) Anders Celsius was born in Uppsala, Sweden, in 1701 into a family of scientists. One of his grandfathers was a mathematician, the other an astronomer, as was his father. Anders himself became a professor of astronomy at the age of 29. He went on several geographical expeditions, including some to polar regions and the equator to compare the length of a degree along a line of longitude in both places. His measurements confirmed Isaac Newton’s opinion that the Earth was slightly flattened at the poles compared to a perfect sphere. This expedition helped make Celsius famous, and enabled him to raise funds to build the Uppsala Observatory, where he became director. Celsius is most famous for inventing the Celsius temperature scale, in which, interestingly, he made the boiling point of water zero degrees, and freezing point 100 degrees (the opposite of today’s scale). In 1745 Carolus Linnaeus reversed this to the scale we use today. Celsius contributed to astronomy by making many observations, including measuring the brightness of 300 stars. To do this, he tested how many glass plates were needed to stop light from each star getting through. It took 25 glass plates to stop light from the brightest star in the sky, Sirius, from getting through.

Conduction—vibrations pass along from particle to particle away from the heat source.

than liquids because the particles in a solid are packed closer together. Among the metals, copper and gold are particularly good conductors. Gases are less efficient conductors than liquids, as the particles in a gas are Cool pools spread out much more. you jump into a When Poor conductors are called swimming pool, the water insulators. The reason many gives you a shock, even if it substances are poor conductors is at the same temperature as the surrounding air. Why? (insulators) is that they contain Water is a much better trapped air, which is a gas and a conductor of heat than air, notoriously bad conductor. so though we may be

Fig 5.2.1

heat conducted in this direction

Prac 1 p. 125

conductor than the air surrounding the rest of your body, and conducts heat away from your feet, leaving the particles in them vibrating less and feeling cold. Different substances conduct heat at different rates. Metals are generally good conductors of heat, whereas non-metals like paper, wood and plastics are not. Compare the water tap in the laboratory with the desktop or your book. Which feels the coldest? Solids are better conductors

metal rod

good conductor

Fig 5.2.2

Esky

Prac 2 p. 126

comfortable in air at 20°C, water at the same temperature conducts heat away from our bodies more rapidly, leaving us feeling colder for a while.

Useful insulation

Firewalking Firewalking is not due to any special magical powers. With the right type of coals (pure charcoal), just a thin outer layer is on fire and only a small amount of heat needs to be conducted out of the burning coals to the foot for the coal to stop burning. Because pure charcoal coals are porous (contain many small holes), it takes about a second for enough heat to conduct from within the coal to the foot before any harm is done. At normal walking pace each foot is in ground contact for only half a second, so there is plenty of time for a firewalker to cross a few metres of hot coals.

H2O

poor conductors

Many animals make use of the poor conducting ability of air by having thick fur coats or feathers that trap air and insulate them against harsh, cold conditions. Some animals even grow a thicker ‘winter coat’. Jumpers, blankets and sleeping bags contain fibres (hair or feathers) that trap air and insulate against the cold. Fur and feathers provide good insulation by trapping air.

Fig 5.2.3

gas

very poor conductor

Different substances have different conducting abilities.

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UNIT

5.2

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Heat There are many examples where insulators are useful in the kitchen. Saucepan handles, oven mitts and pot stands are all made of poor conductors to prevent burns to people or surfaces.

oven mitt

insulated handle

Fig 5.2.4

saucepan

pot stand

Insulation in action in the kitchen

The walls and ceilings of many buildings contain fibreglass insulation batts that trap air within fibreglass fibres. Double-glazed windows have two layers of glass (instead of the conventional one sheet) with an insulating layer of air trapped in between. The space shuttle’s surface is protected by tiles made of insulating material to protect against the heat generated on re-entry to the Earth’s atmosphere. When these tiles are damaged the effect can be disastrous: on 1 February 2003 the space shuttle Colombia broke up on re-entry, 60 kilometres above Texas, killing all seven of its astronauts.

R ratings Insulation batts are often given ‘R’ ratings. The R stands for resistance to heat flow. The R ratings for 2.5 cm thicknesses of some materials are given below.

Material Insulation batt

120

R rating 4.0

Polystyrene foam

4.5

Chipboard

2.0

Wood

2.3

Window (single glazing)

0.9

Window (double glazing)

1.6

Fig 5.2.5

Convection

Insulation batts being installed in a house

Prac 3 p. 126

In liquids and gases, more heat is transferred by convection than by conduction. The particles in a solid have fixed positions and can only vibrate, whereas the particles in liquids and gases can actually move about. They can easily carry their heat energy with them, spreading the heat to other parts of the substance. The spread of heat due to the movement of particles in liquids and gases is called convection. When a liquid or gas is heated, the particles in the heated region become more spread out, or less dense. Liquid or gas that is less dense than the rest of the substance will rise, taking heat with it. You may be familiar with the expression ‘hot air rises’—hot air balloons rise due to the less dense hot air within the balloon. Smoke and air rise above a fire for the same reason.

Fig 5.2.6

Hot air rises.

UNIT

5.2 Hot water systems have heating elements or flames at the bottom of the tank because convection will cause the heated water to naturally rise and mix with the remaining colder water. Central heating vents are usually in the floor, as the hot air will rise to warm higher regions. The roof cavity of a home will often be noticeably warmer than floor level for the same reason. When warmer air rises, cooler, denser air moves in to fill the space left behind, resulting in convection currents. Solar hot water systems also make use of convection as shown in Figure 5.2.8. Prac 4 p. 127

Fig 5.2.8

A solar hot water system

radiation from sun

to hot water taps

to hot taps

cold water

hot water rises convection current

cold water

roof

cold water sinks boiler

Fig 5.2.7

warmed water rises

A basic hot water system showing the movement of water by convection

Conversely, colder liquid or gas will sink. When an upright freezer’s door is opened you may feel the cold air as it falls onto your feet. Supermarket freezers that are upright have doors, while the ‘tub’ type do not, as the cold air cannot escape as easily.

Wind and sea breezes Wind is caused by hot air in one region rising and its place being Gliding taken by colder air coming in from Gliders use convection another region. For example, air at currents in the air to the equator is hotter than air at the stay aloft much longer than would otherwise poles, causing global winds. be possible. During the day a sea breeze occurs because the land warms up more quickly than the sea. As warm air rises above land, cooler air moves in from just above the sea to replace it. The opposite occurs at night, when the land loses heat more quickly than the sea.

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Heat

warm air rises

air cools and drops

cool air rushes in to fill space left by warm air

warmer land

cooler sea

A sea breeze during the day

All objects give out heat radiation—the hotter an object is, the more heat it radiates. Dark objects tend to give out more radiation than shiny or lightcoloured ones at the same temperature. Another good example of radiated heat is an open fire. Red-hot coals give out a great deal of radiation. If someone stands between you and the glowing embers, you notice the loss of radiated heat immediately! An electric radiator gives the same effect.

air cools and drops cool air rushes in to fill space left by warm air

warm air rises

Killer heat

warmer sea

cooler land

Prac 6 p. 128

In bushfires, it is often radiant heat that is deadly—it can kill well before flames actually reach the victims.

A land breeze at night

Fig 5.2.9

Two sources of radiation

How sea and land breezes work

Radiation When you step outside into bright sunlight, you often feel the warmth of the Sun on your skin. Heat from the Sun cannot reach us by conduction or convection because space is a vacuum. There are no particles between the Sun and Earth to pass along vibrations or move in convection currents. How then does heat transfer from the Sun to the Earth? The answer is radiation. Radiation is the transfer of heat energy by invisible waves and does not need a material to travel through. Heat radiation is sometimes referred to as infra-red radiation and travels at the speed of light. In fact, infra-red radiation and visible light are both types of electromagnetic waves. You will learn more about these and other waves later on in Science. Prac 5 p. 127

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Fig 5.2.10

Absorption, reflection and transmission

The thermos flask

Infra-red radiation may be absorbed, reflected or transmitted when it hits an object (in reality, a combination of all three). You may have noticed coils of black hose on the roofs of some houses. These may be connected to hot water systems or swimming pool heaters. Black is used as dark objects are good absorbers of radiation. Black cars tend to heat up more than lighter-coloured ones, and people in hot climates wear light-coloured clothing to reduce the amount of radiation they absorb, and therefore stay cooler. Windows are good transmitters of radiation.

The thermos flask is constructed to minimise all three possible ways of losing heat. The walls of the flask are made of two thin layers of glass with a vacuum between to prevent heat loss due to conduction and convection. The glass walls have a silvered coating to reduce emitted radiation.

UNIT

5.2

stopper polythene vacuum

silvered walls can

hot liquid

polythene

absorption

Fig 5.2.11

UNIT

5.2

reflection

transmission

When radiated heat meets an object, three things may happen.

[ Questions ]

Checkpoint Energy and heat 1 Identify three sources of heat.

A vacuum flask prevents heat loss by all three methods of heat transfer.

Fig 5.2.12

Summary Heat may be transferred by: • conduction—the passing of vibrations from particle to particle • convection—the movement of particles from one place to another • radiation—where no substance is required to aid the transfer.

2 Explain the difference between temperature and heat. 3 Identify the three ways that heat can move from one place to another.

Conduction 4 Explain how conduction occurs in terms of particles. 5 For heat to conduct from one solid to another, two things must happen. Explain what these two requirements are. 6 Draw a particle diagram to demonstrate conduction in a metal rod. 7 List the following in order from best to worst heat conductor: water, air, copper, outer space. 8 Identify another name for a poor conductor. Give an example.

9 Explain how a fur coat insulates the person who wears it. 10 Describe what double glazing is and when it is used.

Convection 11 There are many differences between convection and conduction. Explain some of these. 12 Draw a diagram to demonstrate convection currents in a beaker of water being heated from underneath by a Bunsen burner. 13 Draw a diagram to demonstrate how a sea breeze works.

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Heat

Radiation 14 Identify a household device that gives out both light and radiated heat. 15 Explain why cloudy nights are usually not as cold as nights when the sky is clear.

Think 16 Explain how some supermarket freezers can be open at the top without losing too much cold air. 17 Explain why you often feel a draft when someone leaves a door open on a cold night. 18 Explain why heat cannot reach the earth from the Sun by conduction or convection. 19 Propose the best colour for the following things (and explain each choice you have made). a solar heating panels b the outside of a house in a hot country c a car radiator, where heat is required to be lost d a fire-fighting uniform

27 An open fire in a lounge room is an inefficient way to heat a house, but enclosed wood heaters are better at heating a home. Explain why. 28 Some central heating systems release hot air into a house through vents near the ceiling. Explain why this is a poor design.

Skills 29 Construct a column graph to display the R values for the table on page 120.

[ Extension ] Investigate 1 Investigate how radiation is involved in the greenhouse effect. 2 List the ways your house uses or prevents heat transfer.

20 Identify the type of heat transfer that applies in each case below. a No material is required. b Particles vibrate. c Particles move through a material.

3 Investigate how dinosaurs such as dimetrodon were able to absorb and emit heat. Are there animals today that use similar methods to absorb and emit heat?

21 Identify the correct statement and copy it into your workbook. A Black objects are better emitters but poorer absorbers of heat than white objects. B Black objects are better emitters and better absorbers of heat than white objects. C Black objects are worse emitters and better absorbers of heat than white objects. D Black objects are worse emitters and worse absorbers of heat than white objects. E The colour of an object does not affect how it emits or absorbs heat.

4 Make a ‘heat motor’ based on the design shown here. The spiral must be made from aluminium, not paper or cardboard.

Action

DYO

thread

stand

22 Identify an example of each type of heat transfer. 23 Explain how a thermos keeps food hot by reducing all three types of heat loss. 24 a Identify four devices or inventions that have something to do with heat energy. b Evaluate the importance of each device to society.

Analyse 25 Propose why the outside of a kettle is often shiny. 26 A saucepan full of water is heated on an electric hotplate. Explain the different types of heat transfer happening.

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flame from match or Bunsen burner

Fig 5.2.13

5 Try the experiment illustrated here. The flame should go out due to the heat absorbed by the copper spiral lowering the temperature below that needed for combustion to occur. 6 Make a chimney machine as shown here, and explain its operation.

UNIT

5.2 Project match (lit)

coil of copper wire

Flame snuffer

An energy-efficient home Design a home that requires minimum heating in winter and minimum cooling in summer. Present your final plan in poster format, with the energy-efficient features labelled. Estimate the cost of the features you include, and compare these to the possible savings on fuel and energy bills.

Fig 5.2.14 Fig 5.2.15

smoke

candle

UNIT

5.2

[ Practical activities ]

blob of wax

Conduction in metal rods Prac 1 Unit 5.2

Aim To compare the heat conductivity of different metals

Bunsen burner

tripod

Equipment Three rods made of different metals (e.g. iron, copper, brass), candle, tripod, Bunsen burner, heat-proof mat, timer

Method 1 Assemble the apparatus as shown in Figure 5.2.16. Melt a piece of candle wax at regular intervals along each rod. (Alternatively, use a temperature probe to monitor the temperature at the end of each rod for a given time.) 2 Begin heating the non-waxed ends of each rod, and time how long it takes each blob of candle wax to melt. 3 Stop heating after 5 minutes, if not before.

heat-proof mat

Fig 5.2.16

Questions 1 List the rods in order from best to worst conductor. 2 Present your results as a graph.

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Heat

Prac 2 Unit 5.2

Conduction in water

Insulators

Aim To investigate the ability of water to conduct heat.

Aim To compare the insulating properties of different materials

CAUTION: The test tube may crack during this experiment. Make sure you wear safety glasses. Use great care in heating the test tube, moving the tube continually in the flame.

Equipment Bunsen burner, heat-proof mat, test tube, small ice blocks, steel wool, safety glasses, test tube holder

Method 1 Heat a test tube containing ice, water and steel wool as shown, moving the tube continuously. Use the steel wool to hold the ice at the bottom of the tube. Make sure you heat at the middle of the test tube, above the steel wool, as shown in Figure 5.2.17. 2 Heat the water until it begins to boil. Fig 5.2.17

water steel wool ice

Prac 3 Unit 5.2

Equipment

Two soft drink cans or small metal containers, insulating materials (e.g. cloth, cotton wool, foam, rubber, newspaper, carpet scraps, fibreglass insulation), thermometer or temperature probe, hot water, beaker, timer

Method 1 Surround one can or container with a layer of one of the insulating materials. Leave the other can uncovered. This can is called a control. 2 Use a beaker to measure a certain amount (e.g. 100 mL) of hot water into both. (Note: you will need hot water of the same temperature later in this experiment.) 3 Place a thermometer or temperature probe in the cans and record the temperature every minute for 10 minutes. 4 Repeat steps 1 to 3 for each of the other insulating materials, making sure the hot water is at the same temperature as that used previously.

thermometer

insulating material

Fig 5.2.18

Extension 5 Try different thicknesses (number of layers) of a particular material. 6 Repeat the experiment, but instead of using hot water, use cold water, and attempt to heat the containers using sunlight or other suitable heating sources.

Questions 1 State whether the ice fully melts before the water boils. 2 Describe what this experiment tells you about the heatconducting ability of water.

Questions 1 Present your results in a table. 2 Draw a line graph for each container on the same set of axes. Put time along the horizontal or x-axis. Label each graph. 3 Identify which material is the: a best insulator b worst insulator 4 Explain why one container was left uncovered.

126

Purple convection currents Prac 4 Unit 5.2

Aim To observe convection currents in water. Equipment

Radiation emission Aim To find what colour best Prac 5 Unit 5.2

radiates heat energy

Equipment

A single crystal of potassium permanganate, a 250 mL beaker, Bunsen burner, tripod, gauze mat, heat-proof mat, glass tube or straw

Two cans (one black and one silver or white), measuring cylinder or beaker, two thermometers or temperature probes, hot water, beaker, timer

Method

Method

1 Assemble the apparatus as shown in Figure 5.2.19, except for the crystal of potassium permanganate. Fig 5.2.19 crystal of potassium permanganate

UNIT

5.2

1 Fill each can with an equal amount of hot water at the same temperature. 2 Place a thermometer (or a temperature probe) in each container and record the temperature every minute for 20 minutes. 3 Record your results in a table.

glass tube or straw

water

thermometer

thermometer

beaker

Bunsen burner

tripod

heat-proof mat

Fig 5.2.20

2 Use a glass tube or straw to gently place the crystal at the bottom of the beaker. (You could try several small pieces of paper instead of potassium permanganate.)

Questions

3 Heat the beaker and observe what happens.

1 Draw a line graph for each container on the one set of axes.

Questions

2 Identify which material is the:

1 Sketch the pattern formed by the moving potassium permanganate particles at several stages of the experiment.

a better emitter of heat b worse emitter of heat 3 It was important that the water in each can was at the same temperature at the start. Explain why.

2 Explain why the particles moved in the path they did. 3 Explain where you would find similar convection currents in the home or industry.

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Heat

Radiation absorption Prac 6 Unit 5.2

AIM To find what colour best absorbs radiated heat energy Equipment

Two thermometers or temperature probes, black card, white card, two retort stands with clamps, a 100 W light globe, heat-proof mat

Method 1 Attach the black card to the bulb of one thermometer, and the white card to the other as shown. (Alternatively, use a temperature probe and study one surface at a time.) Ensure the cards are the same size. 2 Clamp the thermometers and place them on either side of the light globe. 3 Measure and record the distance between the globe and the card. Ensure the globe is placed exactly between the two thermometers. 4 Connect the light globe to a power point and switch on. 5 Record the temperature on each thermometer in a table like the one below.

Time (minutes)

1

2

3

Fig 5.2.21

4

Temperature (°C) (black) Temperature (°C) (white)

6 Repeat steps 3 to 5 with the cards twice the distance from the globe.

Questions 1 Identify which colour card absorbed radiation the best. 2 In this experiment the light globe must not be closer to one thermometer than the other. Explain why. 3 Explain why the same-sized card should be used on each thermometer. 4 State what happened to the temperature when the cards were twice the distance away. Propose a reason for this observation.

128

5

6

7

8

9

10

UNIT

5. 3

Non-luminous

context

Luminous

You see it every day and use it every night. Without it you cannot see. What is it? It’s light! Light is the fastest form of energy known. It travels at 300 000 kilometres per second and does not need a material to travel through. (Just as well, as it has to travel through the vacuum of space.) At this speed light only takes about eight and a half minutes to travel 150 million kilometres from the Sun to the Earth.

Fig 5.3.1

The Sun

Fig 5.3.2

The Moon

Fig 5.3.3

A red traffic light

Fig 5.3.4

A tennis ball

Luminous and non-luminous We see objects because they either emit their Prac 1 own light (such objects are called luminous) p. 134 or they reflect the light coming from something else (non-luminous). Most objects that we see are non-luminous. We see them only because they reflect sunlight or artificial light (e.g. from a light bulb) to our eyes. Figures 5.3.1 to 5.3.4 show some examples of luminous and non-luminous objects. Why is the The Sun and a light bulb sky blue? are examples of incandescent Sunlight is actually objects—objects that give out made up of the colours both heat and light. A firefly and of the rainbow. When sunlight enters the an angler fish are examples of Earth’s atmosphere, bioluminescent creatures—living particles in the things that emit light without heat. atmosphere scatter the

Shadows

blue light more than other colours, spreading blue light in the sky.

Shadows are formed when an object blocks the light aimed at a surface. We can predict the position and type of shadow (sharp or fuzzy) using the fact that light travels in a straight line. The term umbra is used to describe a full or sharp shadow. When a larger light source is used, the shadow formed consists of a small umbra and a much larger partial shadow called the penumbra. The effect of the size of the light source on the shadow produced is shown in Figures 5.3.6 and 5.3.7.

The angler fish uses bioluminescence to attract prey.

Fig 5.3.5

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Light Shadow formed using a small light source

Fig 5.3.6

object

We measure these angles between the rays and a line called the normal, which is drawn at right angles to the surface.

full shadow (umbra)

small (point) source of light

screen

Fig 5.2.8

Regular reflection

full shadow (umbra)

larger light source

object

partial shadow (penumbra)

Fig 5.3.9

Diffuse reflection

screen

Fig 5.3.7

Prac 2 p. 135

Shadow formed using a larger light source Reflection at a plane mirror

Fig 5.3.10

Reflection Reflection occurs when light rays ‘bounce’ off a surface. There are two main types of reflection: regular and diffuse. Regular reflection occurs at a very smooth surface, such as a mirror or polished metal, and forms a clear image in it. If we cannot see a clear image, then diffuse reflection has occurred— for example, light may reflect from a tabletop, but not well enough to form a clear image. Even though it appears smooth, a tabletop surface is quite rough compared to a mirror. Both types of reflection obey the law of reflection. This law states that the angle of the incoming ray is always equal to the angle of the reflected ray.

130

incident ray

mirror

angle of incidence angle of reflection al

rm

no

reflected ray

Images and ray tracing

Uses of plane mirrors

When you look in a flat or plane mirror, you see an image of yourself the same distance behind the mirror, yet you know there is actually no one there. Such an image is called a virtual image. Virtual images can be identified when it is known that the light does not actually come from the image (in this case, light does not come from behind the mirror). The law of reflection explains how virtual images are formed. Because our brains are ‘programmed’ to expect light to travel in straight lines, they, in conjunction with the eyes, trace back reflected rays and assume Prac 3 p. 135 that is where the light came from.

Mirrors are used in many clothes shops for obvious reasons. Figure 5.3.12 shows that in order to see your whole body in a plane mirror, a mirror only half your height is needed if it is placed at the right level.

Image formation in a plane mirror

You do not need a mirror the same size as yourself to see your whole body.

UNIT

5.3

Fig 5.3.12

mirror 1m 2m

Fig 5.3.11 1m

Incident ray

Object

Virtual image

Have you noticed how the image of writing appears the wrong way around in a mirror? This effect is known as lateral inversion. Emergency vehicles such as ambulances and fire engines often have their names written back to front so they are easily read in rear-view mirrors.

Mirror Eye

Reflected ray

Two-way mirrors (‘the Consider a two-way mirror with a person the subject’) on one side, and an observer on and , room lit tly brigh a in is ct other. If the subje ct the observer is in a darkened room, the subje of back and front the from ted reflec only sees light back of the glass—that side acts like a mirror. The thin the mirror may be coated with a layer of metal d enough to allow some light to be transmitte through to the observer. The darkened side that side reduces the chance of light passing from the ng keepi fore there side, ct’s to the subje observer hidden.

The back-to-front writing will appear the correct way around when seen in a rear-view mirror.

Fig 5.3.13

A periscope makes use of reflection to allow the user to view an image of something at a higher level. Note how the image is at the same level as the user’s eye.

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Light

An accurate reading is obtained when the pointer covers its image.

Fig 5.3.15 object

30

40 image of pointer pointer

mirror

60

0

periscope

50

10

20

virtual image

Fig 5.3.14

In a periscope, two parallel mirrors produce a virtual image.

Reading meters A mirror strip in meters, such as those used in electronics, allows a more accurate reading to be taken by lining up the pointer and its image.

Worksheet 5.3 Applications of laser light Prac 4 p. 136

UNIT

5.3

[ Questions ]

Checkpoint Luminous and non-luminous 1 Explain how we can we see a basketball even though it does not produce its own light. 2 Identify five examples of: a luminous objects b non-luminous objects 3 Identify three incandescent objects. 4 Copy and complete: A glow-worm is an example of a _____luminescent creature.

Shadows 5 Explain how a shadow is formed. 6 Clarify the meaning of the term ‘penumbra’. 7 Describe how a shadow changes when an object moves towards a screen. Assume the light source is small.

Reflection 8 Clarify the terms below by writing a definition for each. a reflection b diffuse reflection c law of reflection d normal

132

9 Identify another example (besides a tabletop) of a surface that would most likely produce diffuse reflection. 10 Copy and complete Figure 5.3.16, labelling the angle of incidence, angle of reflection, incident ray, reflected ray and normal.

Uses of plane mirrors 11 Describe two uses of plane mirrors.

Think 12 Explain the evidence that suggests that light does not need a material to travel through. 13 Calculate how far light could travel in: a 2 seconds b 60 seconds c 1 hour 14 Copy Figure 5.3.7, which shows a large light source, an object and its shadow on a screen. Underneath, draw a similar diagram, but make the object closer to the screen. 15 The Sun is a very large and wide source of light. If instead it was a tiny but bright point source of light, explain how the shadows on Earth would be different.

Fig 5.3.16

UNIT

5.3

16 Write the word EMERGENCY VEHICLE so that it would appear correctly when viewed in a mirror. 17 When a periscope is used, identify where the following are normally located. a the object b the image 18 Other than those examples used in this unit, identify two other situations where plane mirrors are used. 19 a Identify four devices that use light to perform a task. b Evaluate the importance of each device to society.

Analyse 20 Copy Figure 5.3.17 and draw the reflected ray for each incident ray.

mirrored surface

Fig 5.3.18 22 In a clothes shop, a plane mirror is needed that allows people up to 180 cm tall to see themselves in it from head to foot. Calculate what length the mirror should be. 23 Redraw Figure 5.3.12 but place the person further from the mirror. Use rays to demonstrate that they can still see themselves from head to foot.

Create

Fig 5.3.17 21 Copy and complete Figure 5.3.18, showing how the image is formed.

24 Design a new device that uses a plane mirror(s) to help solve a problem or make a job easier. a Describe the problem you are trying to solve. b Describe how your device will overcome the problem. c Draw a labelled diagram of your device. Include rays to show where the light will be reflected. d Design an advertisement to sell your device to the public.

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Light

[ Extension ]

4 Research what an aurora is and make a presentation to the class about this.

Investigate

5 a Investigate and report on how fibre optic cables transmit light. b List the advantages and disadvantages of fibre optics. c Evaluate the benefits that fibre optics may have for society.

1 Research what is meant by both a solar and a lunar eclipse. Draw diagrams to explain the differences. 2 Find out how a kaleidoscope works. 3 Research how lasers use reflection to produce stronger beams.

UNIT

5.3

[ Practical activities ] The pinhole camera

Prac 1 Unit 5.3

Aim To show that light travels in a straight line.

tape to join sections

Equipment A small cardboard box (e.g. a shoebox), aluminium foil, tracing paper, masking tape, a candle, scissors

foil

Method 1 Remove a section from each end of the box, and replace it with foil at one end and tracing paper at the other. Seal all gaps with masking tape. 2 Make a small hole in the centre of the foil using a compass point or similar small point.

candle pinhole

screen (tracing paper)

viewing hole

3 Place a lit candle about 30 cm in front of the pinhole/foil end of the box. 4 Make sure the room is as dark as possible. Observe the image formed at the tracing paper end of the box.

Fig 5.3.19

Pinhole camera

Fig 5.3.20

5 Investigate the effect of moving the candle to different distances from the pinhole. 6 Investigate the effect of increasing the size of the pinhole.

Questions 1 Compare the pinhole camera with a real camera. What section represents the film? 2 Copy and complete Figure 5.3.20. Which way up is the image? 3 Explain what happens to the image when: a the candle is moved further away from the camera. b the hole is made larger.

134

candle pinhole

tracing paper

UNIT

5.3 The law of reflection Aim To investigate the law of reflection Prac 2 Unit 5.3

Equipment A light box and power supply, ruler, mirror, protractor or Mathomat, plain paper

to power supply (12 V)

mark reflecting surface mirror

Method 1 Assemble the equipment as shown here, marking the position of the back of the mirror and the normal. normal

2 Mark the position of the incident and reflected rays.

mark each ray with two dots

3 Measure the angle of incidence and angle of reflection and record your results in a table. 4 Repeat steps 1 to 3 for several different angles of incidence.

Questions 1 Explain why the back of the mirror is marked and not the front.

Fig 5.3.21

2 Draw a conclusion about the angles for each pair of rays. 3 Describe some examples of reflection in real life.

Image location

Fig 5.3.22

Aim To locate an image in a plane mirror Prac 3 Unit 5.3

Equipment

mirror

A mirror, plain paper, ruler, a pin or small object (e.g. a nail in a small block of wood)

Method 1 Place the mirror on the paper and mark its position.

ruler

2 Place the object in front of the mirror and mark its position with a small cross. 3 Look at the image ‘in the mirror’ and rule a line of sight on the paper towards the front of the mirror as shown.

pin or other object

4 Place the ruler in a different position and rule another line of sight. 5 Repeat step 3.

line of sight to image

6 Remove the mirror from the paper and continue the lines of sight until they cross each other.

Questions 1 Identify where the lines of sight cross each other. 2 Copy the sentence and complete it by choosing one of the words in brackets: The lines of sight represent _________ (reflected/incident) rays.

3 Rule a line from the cross that marked the pin’s position to where the lines of sight met. State the angle this new line makes with the mirror’s surface. 4 State how far in front of the mirror the pin was. 5 State how far behind the mirror the image was.

135

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Light

The periscope

Method 1 Draw the plan in Figure 5.3.23 onto your sheet of cardboard.

Aim To apply the law of reflection of light by Prac 4 Unit 5.3

constructing a working periscope

2 Score the lines firmly with a pen to aid folding later.

Equipment Cardboard sheet, sticky tape, two mirrors (each approximately 5 x 7 cm, though smaller will do), scissors

3 Attach mirrors where indicated. 4 Fold the periscope together so that the lines indicated form ‘valley folds’, and the mirrors end up on the inside. Use tape to join the edges together. 5 Try your new periscope!

Fig 5.3.23

Questions 1 State the size of the angle at which the light strikes the top of the mirror when the periscope is upright and aimed directly at an object.

attach mirror here

8.5 cm 6 cm

6 cm

2 How could the periscope be made twice as long? Draw a new plan for such a periscope. 3 Propose some uses for periscopes.

6 cm

6 cm

6 cm

6 cm

6 cm

6 cm 8.5 cm

attach mirror here

136

UNIT

context

5. 4 Sound, like light and heat, is a form of energy. We use sound to communicate, for entertainment such as music, and in medical and industrial applications such as fish finders and ultrasound that inspects unborn babies. As we shall see in this unit, using sound has made many tasks more entertaining and easier. Unlike light, sound needs something to travel in. It cannot travel through a vacuum.

no air in jar (vacuum)

no sound detected

Sound cannot travel if no air is present.

Fig 5.4.2

ears, our eardrums also begin to vibrate. In the case of a musical drum, a thin membrane vibrates when struck. Our vocal cords produce vibrations when we speak. air in jar

A sound wave is a series of compressions and rarefactions.

sound detected

Fig 5.4.1

vibrating speaker producing a compression

Fig 5.4.3

air particles

Sound travels through air.

Transmission of sound We hear sounds because something has caused our eardrums to vibrate. Eardrums are small flaps of tissue inside the ear that pass on messages via special bones and nerve impulses to the brain. But how do vibrations reach our eardrums? Sound is produced when an object vibrates and passes these vibrations into the air. Layers of air vibrate in turn, passing the sound energy through the air in a series of compressions and rarefactions that we call a sound wave. When the wave reaches our

compression

rarefaction

speaker producing a rarefaction

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Sound

Tuning forks can be used to show sound vibrations.

Fig 5.4.4

The vibration associated with a sound can be demonstrated by placing the prongs of a struck tuning fork into a beaker of water. A similar effect may be observed if several coils of a slinky are compressed. When the compressions are released they travel from one end of the slinky to Prac 1 the other. p. 144 Sound waves and waves such as the one in the slinky in Figure 5.4.5 are called longitudinal waves, as the particles vibrate in the same direction as that of the sound. Sneaky birds Some birds will hop Another type of wave is the around on the ground transverse wave shown in trying to create vibrations Figure 5.4.6, where the in the ground similar to particles vibrate at right angles those produced by rain. Worms under the ground to the direction of the wave. are tricked into coming to Transverse waves may be the surface to escape produced by shaking a slinky being drowned. sideways rather than releasing compressions. A longitudinal wave in a slinky

Thunder and lightning Have you ever wondered why lightning is accompanied by very loud thunder? Lightning is produced by a build-up of static electricity. It superheats the surrounding air, causing it to expand at a tremendous rate. This expansion produces shock waves in the air that we hear as the sound we call thunder. If you count the number of seconds after a lightning flash before you hear the thunder, you can calculate how far away a storm is. Sound travels at about 300 metres per second in air; so multiply the number of seconds by 300. The result tells you how many metres away the storm is. For example, if you hear thunder 5 seconds after seeing lightning, the storm is about 1500 m or 1.5 km away (5 x 300 ).

138

push then pull repeatedly

compressions

Fig 5.4.5

rarefactions

coil movements

wave direction

wave direction coil movement

Fig 5.4.6

A transverse wave in a slinky

UNIT

5. 4 The speed of sound Sound travels at 343 metres per second in air at 20°C. You may have noticed a delay between seeing a cricketer hit a ball, and hearing the accompanying sound. This is because light sends a message to our eyes at 300 000 000 metres per second! If you were sitting 343 metres from the action, Sonic boom the sound would take On 14 October 1947, Chuck Yeager took his 1 second to reach your ears, X-1 jet aircraft to a speed but the light would take only of 1065 kilometres per 0.000 001 seconds to reach hour, faster than the speed of sound, breaking the your eyes! so-called ‘sound barrier’. Just as a wave travels Such supersonic flight faster in a slinky made of a is nowadays commonly achieved by fighter stiffer spring, sound travels jets and by the now more quickly in liquids and decommissioned solids than in air because the Concorde passenger jet. particles are packed more A loud ‘sonic boom’ is heard as the jet catches closely together. The table up with and passes below shows the sound waves emitted approximate by its engines. This phenomenon is similar speed of sound to a boat travelling faster in some different Prac 2 than the water waves it p. 144 materials. creates in its wake.

Material

Approximate speed of sound in the material (metres per second)

Air at 0°C

330

Air at 20°C

340

Air at 30°C

not to scale

150 m

Using echoes to calculate the speed of sound

Fig 5.4.7

If the speed of sound is known, it can be used to calculate distance or depth. If it takes 1 second for a sound vibration to return to a ship after bouncing off a shoal of fish, then the sound has travelled 1400 metres (from the table above, sound travels 1400 metres per second in water), so the distance to the fish is 700 metres. Sonar on ships and fishing vessels uses ultrasonic sound waves. These are waves travelling faster than humans can hear. This technique is called echolocation. Ultrasonic waves are used in echolocation.

Fig 5.4.8

350

Water

1400

Wood

4500

Steel

5000

Echoes Sound striking a hard wall will reflect back, or echo, towards the source. Echoes can be used to calculate the speed of sound. For example, if the person in Figure 5.4.7 finds that it takes 1 second after making a sound to hear its echo, the sound must have travelled 2 x 150 m or 300 m in 1 second. Hence the speed of sound for the experiment was 300 metres per second.

Some animals use echolocation to avoid obstacles or detect food or objects. Dolphins, piranhas and bats are examples.

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Sound

We call this effect reverberation, and it may take some time to die out as echoes become weaker and weaker. Soft materials such as carpet and curtains absorb the sound energy rather than reflecting it to produce echoes. Concert halls use special sound-absorbing panels to Prac 3 p. 145 reduce reverberation.

Fig 5.4.9

Bats use echolocation to locate objects.

Radar is a similar process to echolocation, except that radio waves are used instead of ultrasound to locate, direct and track various objects over long distances.

Fig 5.4.10

Ultrasound Pregnant women can have an ultrasound to check the development of their unborn baby. This procedure involves using an ultrasound scanner to send sound waves into the woman’s body, where they are reflected at different surfaces (e.g. bone, soft tissue). The echoes are then converted into images on a monitor. Using this method, the patient avoids potentially harmful X-rays or other surgical procedures.

Ultrasound being used to monitor pregnancy

Note the sound-absorbing panels on the ceiling of this concert hall.

Fig 5.4.11

Sound graphs Sound waves may be detected by a microphone and displayed on a cathode ray oscilloscope (CRO for short), a device that converts the pressure variations caused by vibrating layers of air into electrical impulses. The wave displayed on the CRO in Figure 5.4.12 is not a ‘picture’ of the sound produced by the tuning fork, but more like a graph showing how the

microphone

cathode ray oscilloscope (CRO)

Worksheet 5.4 A sonic shock wave generator

Reverberation If you yell out in an empty hall, the echo time is too short for you to detect a distinct second sound. The echo partly overlaps with the original sound, producing a sound that lasts longer.

140

tuning fork

A CRO produces a ‘graph’ of a sound, showing pressure at different times.

Fig 5.4.12

pressure is changing as compressions move through the air near the microphone. The number of compressions that pass a point (e.g. the microphone) each second is called the frequency of the sound. A high frequency produces a high-pitched sound. The CRO displays for some other sounds are shown in Figures 5.4.13 and 5.4.14.

reference sound

Fig 5.4.13

louder

higher frequency

The height of a sound graph indicates loudness. Its horizontal spacing indicates its frequency.

UNIT

5. 4 When played, a clarinet may be thought of as a column of vibrating air particles that also pass vibrations into the surrounding air. A string or air column has a natural frequency that depends on its length. We say the string or column resonates at this frequency. Resonance can be observed when a vibrating object causes another nearby object to vibrate at the same rate. The thin wood of a guitar resonates in response to the vibrating strings. The frequencies of sounds produced by a guitar may be varied by altering the length of the string (by holding the strings at different points) or by tightening or loosening the strings. A clarinet has keys that open or close holes in the column. This changes the length Prac 4 of the air column and the resulting sound. p. 145

Sound levels The decibel scale is used to measure sound and noise levels. We use the abbreviation dB for decibels. Figure 5.4.15 shows some decibel levels of a variety of sounds. Decibel levels for some common sounds

Fig 5.4.15

Decibels (dB) 160 guitar

150

oboe

When spoken, different words and letters produce different sound graphs. These can then be used by voice recognition software to convert spoken words into text on a computer.

The sound of music

Loud

Fig 5.4.14

jumbo jet on take off

130 120

threshold of pain

110

loud thunderclap

100 90 80

train motor mower

70 60

normal conversation

blah blah blah

50

Normal

CRO displays for a guitar, oboe and piano note, which show a repeating, smooth pattern. Noise shows a much messier pattern.

noise

Quiet

piano

Dangerous

Harmful

140

40 30

whisper

20 10 0

quietest sound that can be heard

A plucked guitar string produces sound by passing vibrations into the air.

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Sound For every increase of 10 decibels, we perceive the loudness to have doubled. Noise-producing machinery may be given decibel ratings; for example, a motor mower may be rated at 75 dB. Sounds levels of 120 dB or more can be painful and result in permanent loss of hearing with continued exposure. Earmuffs and sound-proof walls contain material that absorbs sound energy and so protects against high-decibel sounds.

Teacher demonstration Applause Your teacher may have access to a sound level meter or sound probes. If possible, compare the decibel levels of one person applauding with two or three people applauding, and ultimately the entire class clapping enthusiastically. Determine what your teacher thinks is an acceptable noise level for a class.

Worksheet 5.5 The sonic spectrum Worksheet 5.6 Morse code

UNIT

5. 4

[ Questions ]

Checkpoint Transmission of sound 1 Describe a test to prove that sound cannot travel through a vacuum. 2 A sound is transmitted from Person X to Person Y by: A air particles which travel from X to Y B air particles passing vibrations from X to Y C infra-red waves in the same way as radiated heat D heated air particles which transmit heat by conduction from X to Y E none of the above 3 List five sources of sound. 4 Sketch a longitudinal wave. 5 Clarify the following terms by providing a definition for each. a compression b rarefaction

The speed of sound 6 State the speed of sound in air at 20°C. 7 State how far sound would travel (in air at 20°C) in 3 seconds. 8 State how many seconds it would take sound (in air at 20°C) to travel 1 kilometre.

13 Explain the term ‘reverberation’.

Sound graphs 14 True or false? a CRO is short for ‘cathode ray oscilloscope’. b A CRO shows what sound waves would actually look like if air were visible. c A CRO can display a graph of pressure at different times as a sound wave passes.

The sound of music 15 Identify what makes the sound when each of the following is being played. a a violin b a flute c a drum 16 Explain what is meant by the following terms. a frequency b resonance 17 Explain how the frequency of the sound from a guitar string can be changed.

Sound levels 18 Identify the scale used to measure sound levels.

Echoes

19 Use Figure 5.4.15 to identify the sound levels made by: a a jet aircraft on take-off b a motor mower c normal conversation

10 Identify an example of a useful and a not-so-useful echo.

20 State the level at which sound becomes dangerous.

11 Identify two animals that use echolocation.

21 Identify an example of a machine that may produce dangerous sound levels.

9 From the following list, identify the substance in which sound travels the fastest: air at 30°C, water or steel.

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12 Explain an advantage of ultrasound.

Think 22 Explain why empty rooms echo more than furnished ones. 23 A student stands at the end of a road and yells towards a house some distance away. If she hears an echo 2 seconds later, how far is she from the house? 24 There is an old expression: ‘Keep your ear to the ground’. What do you think it means? Propose where it came from. 25 Explain how pushing someone on a swing is similar to resonance in a guitar. 26 a Identify four technologies that use sound in everyday life. b Explain why each technology is important to society.

Analyse 27 A CRO displays the graph shown in Figure 5.4.16.

29 Copy Figure 5.4.15, which shows various decibel levels, and add the following where you think they best fit. a a noisy class b an idling car engine c a telephone ringing d a rock concert e a person shouting

UNIT

5. 4

Create 30 Design a musical instrument that is made from only recycled materials. Your instrument must be able to play the song ‘Twinkle, twinkle little star’. Demonstrate your instrument to the class.

[ Extension ] Investigate 1 Investigate how vocal cords work. 2 Select a photograph of an aeroplane going through the sound barrier and, using this example, explain what a sonic boom is. 3 Using diagrams and a short piece of writing, describe how a piano produces so many different sounds.

Surf 4 Make a model of an instrument called a bull roarer as used by Australian Aboriginals by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 5, and clicking on the destinations button.

Fig 5.4.16 Identify which of the following sounds produced the display above. A a tuning fork C a piano B a guitar D noise 28 Identify which of the displays in Figure 5.4.17 was caused by the loudest sound. Fig 5.4.17

Creative writing What would be the consequences if the speeds of light and sound were swapped—that is, if light travelled at around 340 metres per second in air, and sound travelled at around 300 000 kilometres per hour? Consider one or more situations, for example: • a classroom, sport, transport, communications, traffic, noise pollution • possible new inventions that make use of this new state of affairs • Would a sonic boom still be possible?

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Sound

UNIT

5. 4

[ Practical activities ] A sound cannon

The speed of sound

Aim To make a sound cannon that will blow out a candle

Prac 1 Unit 5.4

Prac 2 Unit 5.4

Equipment A cardboard tube (e.g. a poster tube), plastic Contact covering or cling wrap, masking tape or rubber bands, a match

Method 1 Place the Contact or cling wrap over each end of the tube, stretch it taut and hold it tight with tape or rubber bands. 2 Make a small hole in one end using a pin or compass end.

Aim To compare the speeds of sound and light

Equipment A teacher with a starting pistol, a long tape measure or trundle wheel for measuring 100–300 metres, a stopwatch

Method 1 Measure a straight distance of between 100 and 300 metres with a clear view from the start to the finish. 2 Your teacher should stand at the start with the starting pistol. 3 Several students should stand at the finish with stopwatches. 4 The teacher fires the starting pistol. The students start their watches when they see a wisp of smoke rise from the starting pistol, and stop them when they hear the sound of the pistol. (Alternatively, use a sound detector to determine the time taken for the sound to reach you.)

flame

Fig 5.4.19

small hole (1–2 mm)

Fig 5.4.18

contact or cling wrap

Sound cannon

3 Hold a lit match a few centimetres in front of the hole and sharply tap the other end.

measure distance

Questions 1 Explain what happened to the flame when you tapped the end of the tube. 2 Explain why it is important to seal both ends of the tube, and for the Contact or cling wrap to be tight. 3 Why was the small hole necessary?

5 Calculate an average of the times recorded.

Questions 1 The people with stopwatches started timing when light from the smoke reached their eyes. Explain whether the time this takes is a significant factor. 2 Explain the advantage of calculating an average. 3 Use your average to calculate the speed of sound. To do this, divide the distance (in metres) by the time (in seconds).

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Prac 3 Unit 5.4

Chapter review

Reflection and absorption of sound

[ Summary questions ]

Aim To determine the reflecting/ absorbing capacity of different materials.

1 Explain the difference between energy and work. DYO

Equipment

A sound level meter or sound probe/data logging system, various materials to test as reflectors and absorbers of sound

Method Design an experiment to test and compare the reflecting and absorbing qualities of various materials (e.g. cardboard, glass, wood, plasterboard, curtains).

Measuring cylinder resonance Prac 4 Unit 5.4

Aim To examine resonance in

3 Use examples to explain the following terms: a conservation of energy b energy transformation 4 Choose two appliances used in the home and explain the energy transformations that happen when they are used. 5 Identify the three ways in which heat may be transferred. 6 Copy and complete: Heat flows from one region to any other at a __________ __________. 7 Classify the following as either heat insulators or heat conductors: nail, foam esky, wooden table, plastic cup, barbecue grill, frypan handle, woollen jumper, metal oven tray. 8 a Identify whether water or air is the better conductor of heat. b Explain why.

a measuring cylinder

Equipment 250 mL measuring cylinder, tuning fork

Method

2 List all the types of energy you can, and identify an example of each.

9 Copy and complete: A sea breeze is an example of ____. Fig 5.4.20

1 Strike a tuning fork and hold it at the top of the measuring cylinder. (If a sound detector is available, you may wish to use one to measure the intensity of the sound produced.) 2 Add a small amount of water to change the length of the air column in the measuring cylinder, and repeat step 1. Note whether the sound produced is louder or not. 3 Keep adding water and testing the sound produced when a struck tuning fork is held at the top of the cylinder.

10 Identify an example of radiated heat. 11 State which colour objects best absorb and emit heat. 12 a Explain the difference between a luminous object and an incandescent one. b Identify an example of each. 13 Explain why not all shadows are sharp. 14 Write a definition to clarify the term ‘umbra’. 15 State the kind of waves that sound waves are. 16 Identify which diagram below best represents an actual sound wave.

>>

A

B

Questions 1 Determine the length of air column that has a resonant frequency equal to that of the tuning fork.

C

2 Explain why water is added in small amounts.

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>>> 17 True or false? a Sound needs a material to travel through. b Light needs a material to travel through. 18 a Many applications and uses of science in everyday life were introduced in this chapter. Copy and complete the table below to summarise some of these applications. b Identify two more technologies not listed in the table and add them to your summary.

Technology Ultrasound

Use of technology

Type of energy

Viewing unborn babies

Sound

[ Interpreting questions ] 24 Identify the type of heat transfer that does not require a material. 25 Explain the difference between an echo and a reverberation. 26 A person standing 160 m from a wall hears an echo from it 1 second after calling out. State the speed of sound based on this information. How it works

(heat, light, sound)

Sound waves are sent into the body and reflected back from bones, tissue etc. The reflected sound is changed into an image on a screen.

Thermos Periscope Fish finder (echolocation) Two-way mirror Guitar Solar hot water system Insulation batt

[ Thinking questions ] 19 Identify the energy transformation taking place in each of the following situations. a A car accelerates. b A person running trips and falls over. c A brick is lifted up onto a wall. d A clothes dryer is switched on.

27 A boat is using echolocation to find fish. The signal is sent down into the water and returns to the boat after 1 second. The speed of sound in water is 1400 m/s. a Calculate how deep the fish are. b If the sound returned in 0.5 seconds, how deep would the fish be?

28 A vibrating tuning fork placed on a tabletop causes the tabletop to vibrate at the same frequency. What do we call this? 29 Three sounds are displayed on a cathode ray oscilloscope as shown here. a Identify which sound is the highest in pitch. b Identify which sound is the loudest. c State the unit used to measure sound levels.

20 Draw a diagram to demonstrate a ray of light making an angle of incidence of 30°C with a plane mirror. Also show the reflected ray. 21 a Explain what lateral inversion is. b Demonstrate your understanding of this by writing your name in capital letters, laterally inverted. 22 Identify the type of image that is produced when an object is close to a plane mirror. 23 Draw a diagram to demonstrate how a periscope works.

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A

B

C

Worksheet 5.7 Heat, light and sound crossword Worksheet 5.8 Sci-words

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6

Classification Key focus area:

>>> The nature and practice of science

explain how scientists developed models for the classification of living things classify plants and animals using simple keys

Outcomes

identify whether something is living or not, using the characteristics of life

4.2, 4.8.2

By the end of this chapter you should be able to:

use keys to identify a variety of plants and animals.

something is alive?

2 In which section would you look for Dolly or a surfing magazine at the newsagent?

3 How does a snake warm its blood?

4 Lots of living things are neither plants nor animals. List some of them.

5 What animal uses its whole skin to breathe?

6 Is a taxonomist a taxi driver, a tax agent or a scientist?

7 Is a jellyfish really a fish?

Pre quiz

1 How do we know if

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UNIT

context

6.1 If you were given a rabbit, a Discman, a pencil case and a goldfish, you would have no difficulty sorting them into a group of living things and a group of non-living things. It would be a little more difficult if you were given some pond slime. Although definitely living, it seems to be less lively than the water in a fast-flowing river.

The characteristics of life

So how do we know what is living and what is nonliving? What is it about living things that lets us know they are alive? In order to decide whether something is living we must use a set of characteristics.

Scientists use these characteristics to make it easier to work out if something is living and so that we all agree about what ‘living’ means. Anything that has life is called an organism, including you.

We can tell if something is living or not by looking at its characteristics. Characteristics are typical qualities. For example, two characteristics of kangaroos are that they eat grass and hop on two legs. There are certain characteristics that all living things possess. All living things: • take in and use energy • take in and use gases from the air or water in which they live • produce wastes • respond to stimuli in their environment • are able to move • are able to reproduce • grow.

Coral eating a small octopus to gain energy

Fig 6.1.1

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The water moves, but is it living?

Animals obviously meet all the characteristics of living things. Plants are living things too, although their movement and growth can be so slow that we often don’t notice it. Some things that are not alive may possess some of the characteristics of living things but not all of them. For example, the water in a river can move but it is not a living thing. Among other things, it does not use air or reproduce.

Fig 6.1.2

The oldest plants The oldest plants in Australia are about 2500 years old. Even if you watched one of these plants for your whole life, it is unlikely that you would ever see much happening. It’s hardly any wonder that these plants just seem to be standing there doing very little.

UNIT

6 .1 Living things take in and use energy Animals and plants take in and use energy. This energy is used to move, grow, reproduce and keep functioning. Animals are heterotrophs. This means that they cannot make their own food. They need to eat frequently in order to survive. Animals need much more energy than plants. Animals use glucose, a type of sugar, as their energy source. Glucose is used by organisms in a chemical reaction called cellular respiration. In this reaction, glucose and oxygen are used to produce carbon dioxide, water and energy: glucose + oxygen → carbon dioxide + water + energy

Plants also make energy by respiration but they are able to make their own glucose to carry out this reaction. Organisms that can make their own food are called autotrophs. The chemical reaction that plants carry out to produce food is called photosynthesis. The equation for photosynthesis is the reverse of cellular respiration. In photosynthesis, carbon dioxide and water are used to produce glucose and oxygen:

This plant does not gain energy from the insects it traps—what does it get?

Carnivorous plants Carnivorous plants do exist, but they don’t get any energy from the animals they trap. Most of these plants live in soils that are short of nitrogen, so these plants get their nitrogen from the animals they trap. They then use the nitrogen to help build materials they need to live. One of the largest carnivorous plants in the world, a type of sundew known as Drosera gigantea, which grows to about 1 metre tall, is found in south-west Western Australia.

carbon dioxide + water + energy → glucose + oxygen

Plants capture energy from the Sun to make this reaction happen.

Fig 6.1.3

Fig 6.1.4

Plants absorb energy from the Sun and use it to make food.

Prac 1 p. 153

About two-thirds of the food that humans take in is used to keep us warm. If our bodies are not kept at 37°C, we will quickly become unwell. This is because we are endothermic (more commonly known as warm-blooded). Some animals, like crocodiles, don’t use the energy from their food to keep themselves warm; instead they use the warmth of the Sun. This means that, in spite of their large size, crocodiles don’t eat very much food. Animals like this Prac 2 are said to be p. 154 ectothermic.

Cold blooded? Ectotherms are often mistakenly called ‘cold blooded’. This term is incorrect as these animals do not have cold blood. They just gain their body heat in a different way to endotherms. The temperature of their blood will vary through the day and can be as warm as any endotherm. After all, the Sun can get very hot!

Living things use air Animals take in oxygen gas from the air and use it for respiration. Mammals (including humans) and birds use lungs. These must stay moist so that gases can dissolve and pass easily into or out of the blood. Fish use gills and many very small animals like frogs use their whole body surface to obtain and release gases. Like animals, plants take in oxygen for respiration. Plants must also take in carbon dioxide for the plantbuilding activity of photosynthesis. Plants use their leaves to obtain the gases they need from the air. Leaves have special holes in them called stomata that allow gases to pass in and out. Just like lungs, the inside of the leaf has to remain damp so that the gases can dissolve and move around.

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Being alive Living things produce wastes There are many chemical reactions constantly going on inside organisms. Along with the useful products, these reactions also produce wastes that can become poisonous if they are not removed. Humans get rid of the products of cellular respiration, carbon dioxide Helpful fungi and water, by breathing out. Wast es from living things We also get rid of excess water are sometimes used by by urinating and sweating. other living things. A type Plants use their leaves to of fungus called yeast uses sugar as its energy source get rid of the waste oxygen and produces alcohol as produced by photosynthesis, waste. The alcohol is then and excess carbon dioxide excreted into the liquid that the yeast lives in, making from respiration. wine, beer, whisky, vodka The removal of waste etc. in the process! products from an organism is called excretion. Sweating is one way in which humans excrete wastes.

Fig 6.1.5

Sunflowers turn to follow the Sun.

Fig 6.1.6

Living things move The ability to move by itself is a very simple characteristic of life. Movement also plays a very important role in some of the other characteristics. Reacting to changes and feeding (collecting energy) often rely on movement.

Living things respond to stimuli Organisms react to changes in their environment. The change is called the stimulus—it is the thing that provokes a response. If you hear a loud, unexpected noise you jump. The stimulus was the noise. The response is the jumping. Plants also react to change, but it is not as obvious as when an animal responds. When a plant on a window sill grows towards the light, it is responding to the stimulus of the sunlight. If you could sit and watch a field of sunflowers for a whole day, you would notice that the flowers follow the Sun around the sky, almost like a set of satellite dishes.

150

Fig 6.1.7

Hunting and escape rely on movement and response.

In 1674, when Antoni van Leeuwenhoek first used a very simple microscope to look at pond water, he saw tiny shapes that were moving about. Because they were moving he decided they were alive. He had used one of the characteristics of life to decide that his new discovery was a living thing.

Living things reproduce All living things are capable of reproduction. This means that they can make new individuals that are very similar to themselves. Reproduction can be sexual or asexual. Sexual reproduction generally requires two parents. Asexual reproduction only needs one parent.

UNIT

6 .1 Living things grow and develop As living things become older they tend to become larger, more complicated, or both. This is called growth. Some things grow very slowly, while some grow more quickly. As humans grow they change shape. Have you ever noticed how large a baby’s head is compared to its body? By the time you are fully grown, your head will account for about one-tenth of your body length but a newly born baby’s head makes up about a quarter of its length. Babies’ heads make up a quarter of their length

Fig 6.1.10

Cells Fig 6.1.8

Living things can reproduce—mating red-eyed tree frogs

Male or female? Not all organisms are of one gender, and not all stay the same gender throughout their lives. Animals like slugs and snails are both male and female at the same time, or hermaphrodites. The barramundi, a type of fish found in northern Australia, changes from male to female as it grows. All barramundi under five years old are males, while older ones are all females. Barramundi change gender during their lives.

Fig 6.1.9

There is another characteristic that all living things share that you cannot see with the human eye, no matter how carefully you look. All living things are made up from at least one cell or from things that are made from cells, such as hair or fingernails. This is why we call cells the building blocks of life. As you saw in Chapter 4, nobody knew that living things were made of cells until the microscope was invented. A living thing grows because it has created more cells. A fully grown blue whale contains about one hundred thousand trillion cells!

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Being alive

UNIT

6 .1

[ Questions ]

Checkpoint The characteristics of life 1 Explain what a characteristic is. 2 State two characteristics of humans. 3 List the seven characteristics of living things.

Think 4 Copy and complete the following equation for cellular respiration: glucose + ______ → carbon dioxide + ______ + ______

5 People breathe through their lungs. Explain how other animals and plants breathe. 6 Identify the term used for the removal of wastes from an organism. 7 A person runs up to a seagull and it flies away. In this case, identify: a the stimulus b the response 8 Compare endothermic animals and ectothermic animals by making a list of their differences. 9 Explain the difference between sexual and asexual reproduction. 10 Explain why people didn’t know about cells until the microscope was invented. 11 Plants don’t normally move very much. Describe an example of plants moving of their own accord. 12 Clarify whether organisms have to show all the characteristics of living things to be said to be alive. 13 Identify one non-living thing that displays a characteristic of a living thing. 14 Look around the classroom. Identify one living and one non-living thing that you can see. 15 Plants are living things yet it is difficult to see some of the characteristics of life in them. Explain why.

Analyse 16 Classify the following things as living or non-living, and give a reason for your answer in each case. a a rabbit e a car b a pen f a tree c an apple g a donkey d a human h a rubbish bin

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17 Some robotic toys seem to behave as if they are alive. For example, they indicate when they need ‘feeding’. a List the characteristics of life that they show, and those they do not show. b Evaluate whether these toys could be alive. 18 During the Apollo 13 mission, the astronauts had a problem with the device that removed carbon dioxide from the air they were breathing. a Explain where this carbon dioxide came from. b Explain why we don’t have similar problems on Earth. 19 Imagine that you are in radio contact with an astronaut on the Moon. She has just stood in a strange, squelchy mess and thinks it may be alive. Design a procedure she could follow to find out if it is alive or not. 20 This is a story about a normal person. He does the same sorts of things that we all do but there is one big difference. Aliens from another planet are watching him! They are trying to decide whether he is alive. This is what they see him doing one morning. Jack wakes up when his loud alarm clock rings at 6.45 a.m. He reaches across to the bedside table and turns it off. He also turns on the bedside lamp. The bright light from the lamp makes him blink. After a short while, Jack gets out of bed and walks to the bathroom. He goes to the toilet, takes a shower and walks down the stairs. He can smell toast cooking in the kitchen and he breathes in deeply to take in the wonderful smell. After eating his breakfast, he leaves the house and walks to the ferry. The cold Sydney air makes him cough as he gets on the ferry to go to work. Construct a table to summarise the things that Jack did during the morning that the aliens could use to prove he is alive.

3 When we send space probes to other planets, we often look for evidence of water rather than ‘little green men’. Research and explain why.

[ Extension ] Investigate

Create

1 When people go to foreign countries, they often take travel guides with them. These point out the interesting places to see. These books normally contain a section on the wildlife of the area. Write a section for a travel guide to be used by an alien from another planet that would help them to decide what is and what is not alive on Earth. 2 NASA scientists have recently found what they think may be evidence that there used to be life on Mars. Research what this evidence is and how it relates to the characteristics of life.

UNIT

6.1

4 Create a new organism that shows all the characteristics of life. a Decide in which environment your organism will live. b Either construct a model of your organism using play dough, or present your organism as an artwork or poster. c Make a key to explain how your organism meets the requirements of life. For example, how does it make its energy, move about etc? d Evaluate a classmate’s organism and decide if it is truly alive.

[ Practical activities ] Light and photosynthesis

Prac 1 Unit 6.1

UNIT

6 .1

Method

Aim To investigate how the amount of light affects how much food a plant makes

Equipment A plant that has been left in the dark for several days and a plant that hasn’t OR a plant with several leaves that have been covered with aluminium foil for several days, ethanol, 1 large and 1 small beaker, iodine solution, heat mat, Bunsen burner, tripod, gauze, tweezers, watch-glass

1 Take one leaf that has been left in the dark and one that has not. Make sure they are different sizes so they are easy to tell apart. Record their appearance. 2 Set up a hot water bath. 3 Add the leaves to the small beaker and just cover them in ethanol. 4 Carefully place the small beaker in the hot water bath as shown in Figure 6.1.11. You may need to hold it with a test tube holder.

Step 1

Step 2

Step 3

Cover plant leaves in foil or leave in dark for several days

Boil leaves in alcohol over hot water bath

Cover leaves in iodine solution

leaves

uncovered

covered

Fig 6.1.11

Light and photosynthesis

beaker water alcohol beaker

iodine solution

watch-glass

leaves

>> 153

Being alive

>>> Mustard seeds

CAUTION: Ethanol is extremely flammable. Don’t get it near the Bunsen burner flame. 5 Boil the leaves in the ethanol until most of the green colour has come out. 6 Remove them from the beaker with the tweezers and place them on the watch-glass. 7 Cover them with iodine solution and record their appearance.

Questions 1 Iodine turns purple when it is mixed with starch. The greater the amount of starch in the leaf, the more photosynthesis has occurred. Identify which leaf had the most photosynthesis occurring. 2 Draw a conclusion from this practical.

Prac 2 Unit 6.1

Aim To observe the changes that occur during growth and development of a living thing Equipment

3 small glass or plastic containers, cotton wool, aluminium foil, sticky tape, 30 mustard seeds, plastic wrap, pin

Method 1 Put about 1 cm of cotton wool in the bottom of each container. Moisten it with a bit of water. 2 Add 10 mustard seeds to each one. 3 Place plastic wrap over the top to stop the seeds drying out. 4 Use the pin to make a small airhole in each piece of plastic wrap.

hole cling wrap

container mustard seeds

moist cotton wool

Growing mustard seeds

Fig 6.1.12

5 Completely cover one of the containers with the aluminium foil so that no light can get in. 6 Cover another container in a similar way but this time leave a 1 square centimetre window in the foil near the top of the container. 7 Leave the containers in a safe place for several days. 8 Remove the paper and note any difference in the seeds.

Questions 1 Sketch your results, labelling each container. 2 Explain what this experiment has shown.

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UNIT

context

6.2 There are an estimated 13 to 14 million different types of organisms in the world. So how can we logically organise them? When we are given a large, complicated group of things to organise, the first thing we often do is to sort them into smaller, simpler groups.

Classification Examples of classification can be seen all around us and they make life a lot easier. At the supermarket, items are organised by type or by the way they are packaged. Canned fish will be in one aisle, pasta in another, and sauces and bread somewhere else. Fresh vegetables are in one place, canned ones in another and frozen ones in the freezer. Classification in the supermarket helps us to find what we want. Let’s say you need some maple syrup topping for your ice-cream. Where do you go?

Fig 6.2.1

The books in your school library have been classified—why is this a good idea?

Say you were given a handful of mixed lollies and told to put them into two groups. How would you do it? What characteristics would you use? Scientists use the same practice of putting things into groups of related types. This is called classification.

Even though you may have never used it or seen it before, you know it is probably in the dessert and syrup area. If you then can’t find the maple syrup, you will be able to find something very similar to it because all the similar things are kept together. Your school library organises its books by subject or author. Books on the same subject are in roughly the same place, and novels by the same author are grouped together.

Classifying living things The same thing happens in science when we classify living things. Similar organisms are placed in the same group and so all living things in that group are reasonably similar. The process that sorts all living things into groups is called taxonomy, and Variety of life a person who does this is a So far biologists have taxonomist. described about 1.7 million different species of living In most cases, it is easy to things. This number is only classify an organism as either a a fraction of all the different plant or an animal. However, types of living things that if we are to make sense of the exist on the Earth. It has been estimated that there huge variety of plants and could be as many as 13 to animals we will need to sort 14 million different species them into much smaller of living things on Earth. groups. Scientists use a large number of features to sort living things into groups, but basically they use the way that the living thing is ‘built’ to help them split them into groups. Organisms that have a similar ‘body plan’ will be in the same group and organisms with different ‘body plans’ will be in different groups.

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From kingdom to species Groups of living things Carolus Linnaeus (also known as Carl Von Linne) was an eighteenth-century Swedish naturalist, who in 1753 proposed a way of grouping and naming living things. He divided all animals into six classes: Mammalia (mammals), Aves (birds), Amphibia (including reptiles), Pisces (fish), Insecta (insects) and Vermes (all other invertebrates). In the early 1800s the French zoologist Georges Cuvier made a few changes to the Linnaeus’s system. This set the basis for the classification system we use today. The largest groups are called kingdoms. We will use a five-kingdom classification system: animals, plants, fungi, protists and monera. Carolus Linnaeus— Swedish naturalist

all life

kingdom

phylum

class

order

family

Fig 6.2.2

genus

species

Four, five or six kingdoms? There has been much disagreement among scientists about the number of kingdoms that living things should be divided into. Linnaeus and Cuvier used the information they had available at the time to decide on their two-kingdom model. The microscope has allowed the process of classification to improve to the extent that most biologists choose the five-kingdom classification used in this book. Some biologists like to split up the protists between the animal, fungi and plant kingdoms, depending on their characteristics. This makes four kingdoms instead of five. Debate is still continuing as to whether the protists deserve a kingdom all to themselves. Recent research suggests that the monera should also be divided into two kingdoms, making six in total! Taxonomists continue to argue about the exact number of kingdoms.

156

most organisms with least similarities

Fig 6.2.3

least organisms with most similarities

How we organise living things

If all these terms are hard to remember, you might want to think of a mnemonic—a silly sentence to help remind you. For example, you can remember: Kingdom—Phylum—Class—Order—Family— Genus—Species by remembering: Kind People Can Often Find Green Shoes Can you think of a better one? • A kingdom is divided into smaller groups called phyla (singular: phylum). In the plant kingdom, phyla are often called major groups or divisions. • These phyla and major groups are then divided into classes. • Classes are divided into orders. • Orders can be divided into families. • Families can be divided into genera (singular: genus). • Genera are divided into species.

all living things

fungi plants e.g. rosebush

monera

e.g. mushroom

e.g. bacteria

animals

protists

e.g. kangaroo

e.g. seaweed

The classification of living things in a five-kingdom model

Fig 6.2.4

What is a species?

Naming species

As you move down through this classification, the number of living things in New cat each group gets smaller, but It is not only new living the things in the group species that are being become more similar—that is, discovered. Through s, previously unknown fossil they share more features. As extinct animals are also stated above, when you reach discovered from time to the final group it is called a time. One recent discovery was a million-year-old, species. All members of one sabre-toothed cat skull. species are very similar, but Previously only two kinds not identical. You only have of these cats were known— now there are three! to look at your classmates to realise that all members of the same species are not identical. The easiest way to understand this is to think of a species as a group of things that can reproduce and create young that can also reproduce. Being able to reproduce is called being fertile: a species is a group of similar organisms that can produce fertile young. For example, a Japanese woman and a Scottish man can have a baby together because they are part of the same species—they are both human. On the other hand, a tiger and a frog can clearly not mate and produce young, so we say they are different species. Sometimes two different species that look similar can interbreed. For example, a horse and a donkey can interbreed to produce a mule. But a mule cannot reproduce, since it is sterile.

The practice in science is to be very precise, therefore each species of living thing on Earth has its own unique scientific name. The naming system used by scientists throughout the world was established by Linnaeus in 1753. The system requires that each species be given a name with two parts—its binomial name. The first part of the scientific name is the genus, and is always spelt with a capital. The second part of the scientific name is the ‘specific’ grouping or species, and is always spelt with a lower case letter. Since no living thing can be placed into two different genera, no two living things can have the same scientific name. The scientific names of two types of trees found in New South Wales are Eucalyptus camaldulensis (the river red gum) and Eucalyptus ovata (the swamp gum). They both start with Eucalyptus because they belong to the same genus. The second part represents the species within the genus (i.e. what type of gum tree they are). As another example of classification, let’s look at dogs. The dog has the following classification: Kingdom: Animal Phylum: Chordata Class: Mammalia Family: Canidae Genus and species: Canis familiaris.

Fig 6.2.5

Can you pick Canis familiaris from Felis catus?

UNIT

6. 2

Fig 6.2.6

The offspring of a horse and a donkey is called a mule; it is sterile.

157

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From kingdom to species If this all seems a little confusing, Unit 6.3 should make things a bit clearer.

Fig 6.2.7

Dichotomous key classifying five family pets

Worksheet 6.1 Sifting and sorting Worksheet 6.2 Scientific naming

pets

Introducing keys To make classifications easier to understand, scientists use a model called a key. Keys are simple, easy-tofollow representations of classification systems. The most common type is the dichotomous key. Dichotomous keys have two choices at every point. They start at the top with one group and slowly subdivide until no more choices are possible. These are most often written as flow charts, like the one shown in Figure 6.2.7. This dichotomous key starts with a group of five domestic pets and classifies each animal. The same key for the five domestic pets could also be written in tabular form as Prac 1 p. 160 shown in Figure 6.2.8.

UNIT

6 .2

[ Questions ]

doesn’t live in water

goldfish

doesn’t have big ears

has big ears

rabbit doesn’t breed quickly

breeds quickly

mouse

doesn’t bark

barks

cat

dog

Checkpoint Classification 1 Clarify what classification is. 2 You are given five pieces of fruit: an apple, a pear, a banana, an orange and a grape. List the characteristics you could use to divide them into two groups. 3 Apart from the library and supermarket, identify one everyday place where there is a classification system at work.

1

Lives in water Doesn’t live in water

fish go to 2

2

Has big ears Doesn’t have big ears Breeds quickly Doesn’t breed quickly

rabbit go to 3 mouse go to 4

Barks Doesn’t bark

dog cat

3

4 Explain why classification systems are useful.

Classifying living things 5 Clarify the term ‘taxonomy’. 6 List the terms below in order from the group that contains the greatest number of organisms to the group that contains the smallest number of organisms. Family Phylum Genera Class

Species Kingdom Order

7 Plants are not divided into phyla—state what they are divided into.

158

lives in water

4

The same key as in Figure 6.2.7, but in tabular form

Fig 6.2.8

8 Explain what a species is. 9 Explain how we know that a horse and a donkey are different species. 10 Describe how the unique scientific name for every living thing is created.

Fig 6.2.9

Introducing keys 11 Explain what a key is.

UNIT

6. 2 12 Explain what the word ‘dichotomous’ means when used to describe a key.

Think 13 Identify the class that a dog is in. 14 If you invented a system for classifying the tools used in a car repair shop, would you base your system on what the tools were made of or what they were used for? Explain your answer. 15 Think about the cars in a car park. They all have the same function but there are lots of differences between them. State the characteristics you could use to classify them. 16 A subphylum represents a group smaller than a phylum but bigger than a class. Explain what you think a subclass represents.

22 Using the key in Figure 6.2.10, classify these people.

17 For a long time in history, people tried to name every single new organism they came across and remember them. Explain why this system was doomed to failure. 18 There used to be only two kingdoms of organisms—plants and animals. Now there are four or five, or even six (depending on who you talk to). a Explain why the number of known kingdoms has changed in the past. b Explain why the number of kingdoms may change again in the future. c Explain what this says about the way science works.

people

no freckles

female

no pigtails

pigtails

Louisa

Jane

freckles

male

no hair

hair

Eugene

Ken

Herman

Skills 19 a Design a dichotomous key to classify the contents of your pencil case. Make sure you have at least six different items. b Now present the same key in tabular form. 20 a Write a paragraph to describe the contents of your pencil case. b Explain which is easier to understand: one of the keys you created in question 19 or the paragraph you just wrote. 21 Look at the aliens in Figure 6.2.9. Design a dichotomous key to classify them.

Fig 6.2.10

159

>>>

From kingdom to species

[ Extension ]

Create 3 You have discovered a new species! You must now report your findings to the ‘Royal Society of Science’.

Investigate 1 Investigate what led Linnaeus to come up with his system of classification. Produce an information card that explains your findings and other interesting information about Linnaeus.

Action 2 Design a key to identify the different members of your family or friends. Remember to use physical characteristics.

UNIT

6.2

b Classify your organism into a kingdom. c Outline the characteristics of your new species, especially those that make fit the kingdom you have chosen. d Give your species a name using the binomal naming system.

[ Practical activity ] Making a pasta key AIM To construct a key to classify pasta

Prac 1 Unit 6.2

a Draw a diagram of your new species. Be creative about its characteristics.

Equipment At least 5 different kinds of pasta in large container at front, beaker

Method 1 Using your beaker, scoop out some pasta. 2 Take this to your bench and discuss with your partner/group what characteristics you can use to classify this pasta. 3 Create a dichotomous key to classify your pasta. 4 When you get to the point where you are at a particular type, draw the pasta in that place on your key.

pasta

5 Now create a NEW dichotomous key and reclassify your pasta.

Questions 1 Look at your classmates’ keys. State whether they used the same characteristics that you did. 2 Evaluate your keys. Which do you think was better? Could it be improved?

Start your key off like this.

160

Fig 6.2.11

UNIT

context

6.3 Biologists have used the structural features of animals as the basis for classification. Structural features are how they are physically made up, so if animals have been grouped together it means that they have obvious structures in common. Notice in Figure 6.3.1 that the main structural feature used for classification of animals is whether they have a backbone or not.

Vertebrates Vertebrates are animals that develop a backbone as they grow. They are all members of the phylum Chordata and are called chordates. Vertebrates are divided into five major classes—amphibians, reptiles, birds, mammals and fish.

Major phyla and classes within the animal kingdom

Fig 6.3.1

Tiny animals Large animals are a rare life form, since 99% of all known animals are smaller than a bee!

animal kingdom

vertebrates

invertebrates

have a backbone

don’t have a backbone

fish

birds

e.g. snapper

e.g. kookaburra

amphibians

mammals

no skin covering, live in damp places, lay eggs in water e.g. frog

e.g. human

cnidarians

worms

e.g. jellyfish

e.g. earthworm

sponges

arthropods

millipedes

molluscs

echinoderms

e.g. snail

e.g. starfish

insects e.g. fly

centipedes

crustaceans e.g. lobster

reptiles arachnids skin covered in scales, live mainly on land, lay eggs on land e.g. crocodile

e.g. spider

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>>>

Animal classification Amphibious eyes

Amphibians Amphibians have two stages to their life: many live their early life completely under water and the rest of their lives breathing above water. The best known example of this two-stage life is the frog, which starts life as a tadpole with gills and slowly changes into an adult frog with lungs. These animals have a thin skin that would dry out if they did not live in a damp area. Amphibians Fig 6.3.2

Without goggles, we are not able to focus below the water, so how do amphibians manage to see things both above and below water? The answer is that most of them have flattened corneas (see Figure 6.3.3). This flat cornea doesn’t really do much in air or water, so vision is much the same. Humans have rounded corneas, which give us good vision in air, better than amphibians’, but terrible in water. Amphibians can focus in air and water but their side vision isn’t very good.

have to go back to water to reproduce because their eggs do not have a waterproof coat. Amphibians get heat from their surroundings, making them ectotherms. All belong to the class Amphibia, meaning doublelife (amphis = double, bios = life, in Greek).

cornea

cornea

From egg to tadpole to frog

human

Fig 6.3.3

amphibian

Amphibians have flatter corneas than humans do—this enables them to focus both in and out of water.

Reptiles Reptiles form the class Reptilia (repere = to creep, in Latin). They have dry scales and lungs, and lay soft, leathery, waterproof eggs. Animals similar to modern-day reptiles were the first animals that could live entirely on land. Reptiles include the snakes, lizards, turtles, tuatara, crocodiles and alligators. Many extinct animals (such as dinosaurs) Fossils were reptile too. Today’s Fossi ls have been found reptiles are also ectotherms. By in Australia of a species lying in the sun, their body of goanna that was over temperature can become as 6 metres long. The largest living goanna, high as our own, but unlike us the Komodo dragon, and they cannot retain this heat. lives on Komodo Island This is why they are not very in Indonesia, and is less than half this size. active in cold weather. Some of Australia’s most dangerous animals are reptiles. The saltwater crocodile is feared with good reason. Some of our snakes, like the death adder, taipan and tiger snake, can kill very quickly.

162

A grass snake protecting its eggs

UNIT

6. 3 Fig 6.3.4 crown eyering nape mantle back

rump

lores

forehead upper mandible

lower mandible throat breast

belly

tail

The parts of a bird

Fig 6.3.6

Fish Birds Birds all have feathers, even the ones that can’t fly. They have some scales, but only on their legs and feet. They breathe with lungs and the eggs they lay are hard-shelled. Birds are endotherms. This means they make their own heat by using most of the energy from their food to keep warm. About 900 different species of bird have been seen in Australia. Birds form the class Aves (avis = bird in Latin).

There are many thousands of species of fish. They can be divided into bony fishes (class Osteichthyes), jawless fishes (class Agnatha), and cartilaginous fishes (class Chondrichthyes). The names for these classes all have a Greek origin: • osteichthyes = osteon (bone) + ichthyes (fish) • agnatha = a (without) + gnathos (jaw) • chondrichthyes = chondros (cartilage) + ichthyes (fish). The bony fishes have a skeleton of bone. Most fish fall into this class. Cartilaginous fishes have a skeleton of firm, rubber-like cartilage (the same material that makes up the squashy part of the tip of your nose) and paired fins. Sharks and stingrays are cartilaginous fish. The jawless fishes also have a skeleton of cartilage, but they do not have any paired fins. The great white shark is a cartilaginous fish.

Fig 6.3.5

Fig 6.3.7

Kookaburras belong to the class Aves.

163

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Animal classification There are only about forty-five species of this type of fish. One example is the lamprey. All fish have gills and scales, and most lay eggs. There have been fish in the Earth’s water systems for at least 440 million years. Prac 1 p. 169

Fig 6.3.8

A bony fish—the rainbow trout

• The marsupials give birth to tiny young, which then continue to grow in a pouch. Examples are wombats, possums and kangaroos. • The monotremes are mammals that lay eggs. The eggs hatch after a few days and then the young develop in a pouch. There are only three living species of monotreme: the short-beaked echidna and the platypus, which are found in Australia, and the long-beaked echidna, which is found only in Papua New Guinea. When the first platypus was sent to Europe to be studied, scientists thought it was a hoax because it was so different from the animals they knew. The kangaroo is a marsupial mammal with a pouch.

Mammals All mammals (class Mammalia) are ectotherms, feed their young on milk and have hair. Not all hair is the same: wool and fur are types of hair. On some mammals such as whales, the hair is not obvious, but it is always present, even if only on newborns. The milk is formed in the mammary glands (mamma = breast, in Latin). These two features—hair and mammary glands—are the main features by which we can identify a mammal. The mammals are split into three groups. • The placental mammals give birth to welldeveloped young. Examples are cows, bats, humans and whales.

The cow is a placental mammal, and produces milk in the udder.

164

Fig 6.3.9

Fig 6.3.11

The echidna is a monotreme —a mammal that lays eggs.

Fig 6.3.10

Invertebrates Animals without backbones are known as invertebrates. As can be seen from the pie graph in Figure 6.3.12, most of the animals in the world are invertebrates. There are many phyla within this group. The main ones are the cnidarians, arthropods, molluscs and worms. The relative abundance of different types of animal

Fig 6.3.12

Fig 6.3.13

invertebrates

mammals

Examples of cnidarians are jellyfish, corals and anemones. Many jellyfish are harmless but some, like the box jellyfish, can kill. Many people have felt the nasty sting of a bluebottle, which leaves raised red welts on the skin. One treatment for this is to put vinegar on the welt to destroy the stinging cells left behind by the bluebottle. A cnidarian— the orange cup coral polyp

UNIT

6. 3 Jellyfish There are some amazing types of jellyfish around. A siphonophore is a chain of individuals linked together. At the ends of their tentacles they make fishing-lure type shapes with their own flesh. They jig them up and down. The fish that go for the ‘lure’ end up with a nasty, often fatal, sting.

vertebrates

Cnidarians The cnidarians used to be called coelenterates. They form the phylum Cnidaria (pronounced nid-air-ee-a). About 10 000 species of cnidarians have been identified so far. All Cnidarians have stinging cells and a bag-like body with only one opening surrounded by tentacles. Food goes in this opening and wastes go out. Cnidarians with bodies that attach to something, like a rock, are called polyps. Free-swimming cnidarians are called medusas. Cnidarians mostly live in the sea but some are found in fresh water.

The Great Barrier Reef The only living thing visible from outer space is Australia’s Great Barrier Reef. This is the work of cnidarians. Coral colonies created the reef over thousands of years. When the coral dies, the hard skeleton is left behind. At any time, there is a huge amount of dead coral present in the reef as well as many living colonies. The living colonies are very sensitive. This is why you should not touch the coral when scuba diving around the reef—you could be killing a living colony. A cnidarian—the bluebottle or Portuguese man-of-war

Fig 6.3.14

165

>>>

Animal classification Arthropods The arthropods form the largest animal phylum, the phylum Arthropoda. About 75 per cent of all known animals are part of this phylum. Arthropods are found everywhere—on land, in the air, and in all water systems. They have segmented bodies, paired jointed legs and an exoskeleton. An exoskeleton is a hard outer covering—an external skeleton. Within the arthropods, the major classes are the: • insects (class Insecta) • centipedes (class Chilopoda) • millipedes (class Diplopoda) • arachnids (class Arachnida) Prac 2 p. 170 • crustaceans (class Crustacea). There are close to a million different species of known insects although no doubt there are a lot more yet to be identified. There are more species of insects than any other living thing. Insects have one pair of antennae and their bodies are divided into three sections—the head, thorax and abdomen. They always have three pairs of legs on their thorax. Fig 6.3.15

Centipedes live on land and have one long pair of antennae. Their whole body is segmented and they have one pair of legs on each segment. They have jaws on the first segment and a flattened body. Millipedes also live on land and have one short pair of antennae. Their bodies are also segmented, but tend to be more rounded than centipedes’ bodies. Millipedes have two pairs of legs on most segments.

The parts of an insect

Fig 6.3.17 pronotum forewing head

antenna

abdomen

thorax

ovipositor

chewing mouthparts foreleg

abdominal segment

hind leg

166

Many arachnids live on land but some can live in the water. They have no antennae and only a few body segments. They have four pairs of legs and no jaws. Everyone is familiar with spiders, but these are not the only arachnids. Scorpions, mites and ticks also belong to this class. An arachnid—a rose-haired tarantula

midleg

How old?

Fig 6.3.16

Millipedes on a twig showing two pairs of legs on each segment

The cockroach is an insect that has been almost unchanged for more than 320 million years. It is thought that the cockroach can survive nuclear radiation.

Fig 6.3.18

Crustaceans mostly live in the water. They have two pairs of antennae and breathe through gills. Examples of crustaceans are crabs, prawns and lobsters. A crab is a crustacean.

Fig 6.3.19

cylindrical bodies and a digestive tube with a mouth and anus. Examples of roundworms are hookworms and intestinal roundworms. Flatworms (phylum Platyhelminths, from the Greek: platys = flat, helmins = worm) are similar to roundworms in that they can also be parasitic or freeliving but have flat bodies instead of round ones. If they have a digestive system, it has only one opening. Flukes and tapeworms are examples of flatworms. Annelids (phylum Annelida, in Latin annulus = ring) are also known as segmented worms. They are found both on land and in the water. They have well-developed body systems and segmented bodies. Examples Prac 3 p. 170 are leeches and earthworms. A segmented worm—the different body segments are clearly visible.

UNIT

6. 3

Fig 6.3.21

Molluscs Most molluscs live in the water but a few types live only on land. They have soft bodies, sometimes covered with a shell. They have well-developed internal organs and a large, muscular ‘foot’ for movement. The molluscs are the second-largest phylum of animals and include snails, octopuses, slugs and squids.

Indigenous Australian classification

Fig 6.3.20

A common garden snail showing the large muscular foot

Worms There are three different phyla of worms. The roundworms (phylum Nematoda, from nema = thread, in Greek) are sometimes parasitic. This means that they live off other living animals. Others are free-living in either water or damp soil. They have long, unsegmented,

The scientific term for classification is taxonomy. It is derived from the Greek taxis (‘arrangement’) and nomos (‘law’). Early attempts at classification of living things were done according to need or use. The term ‘fish’ was used to refer to any swimming or aquatic thing. Even today the term ‘fish’ is common to the names shellfish, crayfish and starfish, although there are more anatomical differences between a shellfish and a starfish than there are between a true fish and a mammal. Indigenous Australians used a similar method and classified according to the usefulness or application of the organism. For example,

167

Animal classification penguins were placed in the same category as kangaroos. The reason is that they are both grounddwelling meat sources. Birds were placed in the ‘flying food source’ category. There are also instances of a particular species having no Aboriginal name because it is not used. In a northern area of Australia some Aboriginal tribes named plants according to their uses or their location such as swamp, beach or forest. Fish (guya) are also known according to where they live in the water. This gives five subclasses. Garrwarpuy dwell near the surface Ngoypuy live near the bottom Mayangbuy live in rivers

>>> Raypinybuy live in fresh water Gundapuy live among rocks and reefs In contrast, shellfish and crustaceans (maypal) have at least 10 subclasses. These are determined according to how they attach to rocks or move about and whether they are associated with rocks or reefs. The four distinct subgroups are: Gundapuy attached to reefs and rocks Warranggulpuy move over the outer surface of rocks Lirrapuy move around the edges of rocks Djinawapuy attached beneath rocks or inside coral

Worksheet 6.3 Sorting animals

UNIT

6 .3

[ Questions ]

Checkpoint 1 What is the main thing that biologists have used as a basis for classifying animals?

Vertebrates 2 Explain what a vertebrate is.

10 Identify the two types of cnidarians.

3 Identify the phylum that the vertebrates belong to.

11 Identify the largest animal phylum.

4 Copy and complete the following sentences.

12 a State how many species of insects are known. b State whether you think there are any that are still undiscovered. c Justify your answer to part b.

a Animals that have a backbone of vertebrae belong to the subphylum _________. b The five main classes of vertebrates are amphibians, reptiles, birds, ________ and _____________.

Invertebrates

13 List the main differences between centipedes and millipedes.

5 Explain the difference between a vertebrate and an invertebrate.

14 Identify an example of a mollusc.

6 List the main phyla of the invertebrates.

16 Identify an example of an annelid.

Think

17 Identify two invertebrates that live on land and two that live in the water.

7 Identify three characteristics of each of the following classes. a amphibians d fish b reptiles e mammals c birds 8 Jimbia are animals with hair that lay eggs. Their young then develop in a pouch. Classify the jimbia.

168

9 Classify the following animals as vertebrates or invertebrates. a hamster d mouse g shark b starfish e human h rabbit c snail f dung beetle i earthworm

15 Clarify the term ‘parasitic’.

Analyse 18 A new species of living thing is discovered and it is classified into the same group as an animal with six legs and wings. Identify the other features you would you expect the new species to have. Explain your answer.

19 If you discovered a new species of reptile, list the features it would have. 20 You are watching an animal and it lays an egg. a Identify the groups it could be in. b Explain what else you would need to place it in the correct group.

UNIT

6. 3 Surf 3 Find out more about the classification of the animal kingdom (and others) by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools selecting chapter 6, and clicking on the destinations button.

[ Extension ] Creative writing

Investigate 1 Investigate more about the system used to classify books in the school library and propose what code number would be given to this book if it were in the library. 2 Use the information in Unit 6.3 to make a summary showing how animals are classified. a Gather and include several animal pictures for each group. b Present your information as a poster or PowerPoint presentation.

UNIT

6.3

Australian animals When European settlers first came to Australia they were surprised by some of the animals they found. Explain why this was. When you have found out why, write a letter as if you were one of those first Europeans describing Australian animals to someone in England who has never seen them.

[ Practical activities ] Perch dissection Aim To investigate the internal organs of a fish Equipment

Prac 1 Unit 6.3

1 perch (or similar fish, e.g. mackeral, bream), dissecting instruments, newspaper, something to cover your clothes, gloves, dissecting board

The parts of a perch

ribs

oesophagus

dorsal fins caudal fin

vertebral column

Fig 6.3.22

gall bladder kidney

cranium dorsal aorta

pyloric valve

Method

pharynx

1 Cover your desk completely in newspaper with the board on top. 2 Put your protective clothing on and get your dissecting instruments ready. 3 Get your fish and place it on the board. 4 Observe your fish without cutting. Have someone in your group record your observations. Count how many fins there are. >>

dder a i r b la gonad

stomach

r

live

heart anal fin

spleen

anus bladder

urogenital opening

intestine

pyloric caeca

pelvic girdle pelvic fin

coelom

ventral aorta pectoral girdle pectoral fin

169

Animal classification

>>>

5 Make cuts as shown in Figure 6.3.23 to expose the backbone. You may need to scale some sections first.

1st cut here to expose backbone

Only pick up the scalpel when you are ready to make a cut, and put it back down as soon as you are finished. 6 Turn the fish over and identify the anus. Make a cut from the anus towards the head. Be careful or you will disturb the arrangement of the internal organs.

2nd cut here to expose the internal organs

7 Use Figure 6.3.22 to identify as many of the fish’s organs as possible. Leave the head until last.

Make cuts at the dotted lines.

Fig 6.3.23

Questions 1 The air bladder can inflate and deflate. Explain how this helps the fish.

3 Describe the features of the fish that make it suited for life in the water.

2 Were any organs difficult to identify?

Study of preserved invertebrates Prac 2 Unit 6.3

Aim To examine various preserved invertebrates, noting their characteristics

Database of living things Prac 3 Unit 6.3

Aim To construct an electronic database of living things

Equipment

Equipment

Preserved invertebrate specimens

Access to a computer, database programme (eg MS Access)

Method 1 Use the information in this book to identify as many invertebrates as possible. Try to identify the phylum even if you can’t identify the class. 2 Make sketches of at least three specimens and write some characteristics of these organisms underneath your sketches.

Method 1 Design a draft table on paper to show all of the plant and animal kingdoms and phylum. Include their key characteristics, and examples of organisms in each group. Use the table on page 178 as a guide. 2 Present this draft to your teacher for assessment and feedback. 3 Redesign your table using the teacher’s suggestions. 4 Construct an electronic version of your database that can be used to sort or arrange the data in various ways.

170

UNIT

context

6.4 In addition to the animal kingdom, scientific study so far has led to the separation or organisms into four other kingdoms: plant, fungi, monera and protists. None of these contains the great variety of species found in the animal kingdom but they are interesting nonetheless. The process of science is constantly changing, with many scientists splitting the moneras into two distinct kingdoms.

Plants

nutrients around the plant. Most plants are in this phylum. The main classes of vascular plants are the angiosperms (flowering plants), conifers, cycads, gingkos and ferns. The angiosperms are in the class Angiospermae (angeion = small container, sperma = seed, in Greek). This is by far the largest class of vascular plants. Angiosperms always develop seeds inside the flower, the part that later becomes the fruit. The flowers of The flower is the reproductive part of this plant.

Fig 6.4.2

The parts of a flower

Fig 6.4.3

Scientists have made many attempts to classify plants throughout history, but it was not until the invention of the microscope that a satisfactory system was created. Plants are now classified according to several characteristics—how they feed, their physical features and how they reproduce. The study of plants is called botany. Botanists tend to call the major groups of plants ‘divisions’ but this word means the same as phylum. The main groups within the plant kingdom are the vascular plants and bryophytes.

Vascular plants The vascular plants are in the phylum Tracheophyta (from the Greek, tracheia = windpipe, phyton = plant). Vascular plants contain vascular bundles—cylindrical arrangements of transport cells that carry liquids and

petal sieve tube

small vessels pistil

anther filament

stamen

stigma style ovary

receptacle

ovule large vessel

sepal

Cross-section of the stem of a vascular plant showing the vascular bundles

Fig 6.4.1

171

Plants and other kingdoms angiosperms can range from large, brightly coloured blooms to small, inconspicuous ones that don’t really look like flowers at all. The conifers (class Coniferopsida, conus = cone, ferens = bearing, in Latin) do not produce seeds in fruit like the angiosperms. Instead they produce seeds on the scales of a woody cone. Pine trees are an example of conifers. These trees do not occur naturally in Australia and generally prefer cooler Aboriginal food climates. The Aborigines have Unlike conifers, used many poisonous cycads thrive in tropical substances as food after careful treatment. One environments. They form the example is Cycas media, a class Cycadopsida (koikes = type of cycad. Its seeds are palm-like plant, in Greek). extremely poisonous but can be eaten after roasting Cycads produce seeds in and other treatment. The cones. Some Australian Aborigines didn’t always versions look a bit like share their secrets with palm trees, which is a the early settlers, many of whom fell victim to bit misleading because poisoning after eating palm trees are actually things found in the bush. angiosperms.

>>> The class Ginkgopsida (ginkgo = maidenhair tree, in Japanese) doesn’t have many members—in fact, only one! Ginkgo biloba is a native plant of China. It bears its seeds in cones but, unlike other cone-bearing plants, it sheds its leaves in winter. Ginkgo biloba is now cultivated throughout the world and sold as a natural cure for circulatory problems. Fig 6.4.5

Leaves on a Ginkgo branch

The ferns are in the class Filicopsida (filix = fern, in Latin). They have no seeds and reproduce through spores. The spore cases grow on the leaves and when they are ready they open and release their spores. These spores can give rise to new plants if they land in a good Prac 1 p. 175 place for growth.

Bryophytes The bryophytes are in the phylum Bryophyta (bryon = moss, in Greek) and include the liverworts and mosses. These plants are generally quite small and don’t have a well-developed vascular system or true roots. They are found in moist environments and generally prefer cooler places.

Fungi Fig 6.4.4

172

A cycad

The fungi are a large group and are in the phylum Eumycota (eu = well, mykes = mushroom, in Greek). Fungi are not capable of

How many species? In South Africa’s Cape region, botanists discover new plants every year. They have already identified about 9000 species. If you go for a walk through the forest, occasionally stopping to look at a plant, it is possible that every plant you look at will be a different species.

Harmful bacteria—anthrax

Fig 6.4.7

UNIT

6. 4

Protists Fig 6.4.6

The death cap mushroom

photosynthesis so they can’t make their own food. Like animals, they are heterotrophs—they must feed on other plants and animals to survive. Fungi include mushrooms, toadstools and moulds. Fungi reproduce by spores. Some are very useful. The mould penicillium gives us the valuable antibiotic penicillin.

Monera

Poisonous mushrooms The most dangerous mushroom is Amanita phalloides, commonly known as the death cap. Normally a northern hemisphere plant, it has been found in Australia around Canberra and Melbourne. It has a yellowish to olive-green cap and is the cause of up to 95 per cent of all fatal mushroom poisonings. It doesn’t kill straight away— there are usually no symptoms until about ten hours after it has been eaten. Death can take up to four days.

The kingdom Protoctista (Greek: protos = very first, ktistos = to establish) is a strange kingdom in that its members are all the things that don’t fit in anywhere else. This kingdom contains two phyla: • algae (plant-like) • protozoa (animal-like). All protists live in water. Organisms in this kingdom include seaweeds, slime moulds and amoebas.

Three different types of seaweed

Fig 6.4.8

The members of the kingdom Prokaryotae (from Greek: pro = before, karyon = seed, moneres = single) are also known as monera. All bacteria are in this kingdom. Bacteria are everywhere: in the soil, on your skin and in your intestines, to name just a few places. They can be helpful or harmful. The bacteria in your intestines help to digest your food. However, other types of bacteria can cause serious illness. This kingdom may soon be divided into two kingdoms, being the true bacteria (Eubacteria) and bacteria-like organisms (Archaebacteria).

173

>>>

Plants and other kingdoms

Examples

Characteristics

Chordates

Mammals (including humans), birds, reptiles, amphibians and fish

Vertebrates (have a backbone)

Cnidarians

Jellyfish Polyps

Invertebrates Tentacles Hollow body cavity

Arthropods

Grasshoppers Spiders, crabs, snails

Invertebrates Exoskeleton Jointed legs

Worms

Earthworms, leeches, hookworms

Invertebrates Segmented bodies flat or round

Tracheophytes

Trees, ferns, conifers, flowering plants

Vascular plants (transport system present)

Bryophytes

Mosses, liverworts

Nonvascular plants (no transport system)

Mushrooms, moulds, mildew

Multicellular

Yeast

Unicellular

Monera

Kingdom

Blue-green algae

Blue-green algae

Autotrophic

Bacteria

Streptococcus

Heterotrophic

Algae

Seaweed, diatoms

Autotrophic, plant-like

Protozoa

Amoebae, paramecium

Heterotrophic, animal-like

Fungi

Plants

Animals

Phylum

Protists

Summary: the classification of living things

UNIT

6. 4

1 300 000

10 000 000

270 000

320 000

72 000

1 500 000

4 000

1 000 000

80 000

600 000

[ Questions ]

Checkpoint Plants

Fungi 9 Explain how fungi are like animals.

1 State what the study of plants is called.

10 A few fungi are parasitic. Explain what this means.

2 Identify a word for ‘major group of plants’.

Monera

3 Explain what is special about angiosperms.

11 Explain with examples how bacteria can be helpful or harmful.

4 Identify the part of the flower that contains the seeds in an angiosperm. 5 Explain what sort of seeds conifers produce. 6 State whether conifers occur naturally in Australia. 7 List three characteristics of bryophytes. 8 List the scientific names for the classes of vascular plants.

174

Number Estimated total of species number of currently named species that exist

Think 12 Explain what is so special about protists.

Name of class Vascular plants

—

Angiosperms

Hydrangeas, eucalypts

Examples

Main characteristics

UNIT

6. 4 Contain cells that transport water and food around the plant.

Conifers Cycadopsida Ginkgopsida Filicopsida Bryophytes

No seeds, produce spores on leaves.

—

Fungi

—

Monera

—

Protists

—

Bacteria

13 Complete the table above to summarise the classification of plants. 14 Copy the following, correcting any incorrect statements so they become true. a A vascular bundle cannot transport anything. b Conifers thrive in hot climates. c There is only one plant in the ginkgo class. d Fungi reproduce with seeds.

[ Extension ] 1 Choose one of the people listed below and investigate what they contributed to the classification of plants. Present a two-minute talk to the class about their work and contribution to scientific knowledge. • Theophrastus • Linnaeus • John Ray • Antoine Laurent de Jussieu 2 Research fungal infections of the body such as tinea and ringworm.

15 Explain how ferns reproduce. Present your information as a diagram. 16 Identify three places where bacteria are found.

UNIT

6. 4

[ Practical activity ] Dichotomous key of plants

Prac 1 Unit 6.4

Aim To construct a dichotomous key for plants from the local area Equipment Plant specimens collected from home or around the school under supervision

Method

Questions 1 Give your key and samples to a classmate. Assess whether they could successfully use your key to identify the plants. 2 Evaluate your key. How could your key have been improved?

1 Examine your plants carefully and note some characteristics. 2 Create a dichotomous key to identify the different plants. Include sketches of the plant specimens. If you don’t know their names, you can just call them A, B, C, etc.

175

>>>

UNIT

context

6.5 why keys are used, and review the types already covered. A few new keys that scientists use will also be introduced.

Keys are models that scientists use to make their work easier and more consistent. We have already looked at some different types of keys. In this unit, we will look at

This branching key is not dichotomous because it branches into three or four different groups.

Why do scientists use a key? The main reasons are: • A key makes it easy to identify an unknown object or organism. • A key is easier to use than a page full of writing. • We can see at a glance what characteristics each group has. • All scientists anywhere in the world can use the same key to come up with the same answer (consistency).

mixed lollies

Jellybeans

red

chocolate coated

yellow

other

Maltesers

Turkish delight

bird

does it have fur or hair? no

no does it have a dry skin? yes it’s a reptile

Fig 6.5.2

176

yes it’s a mammal

does the adult have gills? yes it’s a fish

no it’s an amphibian

A dichotomous key for the identification of vertebrates

Fantales

Minties

Smarties

Chocolate creams

If you use a key and you are finding it unclear or difficult to use, then it is not a good key. A good key is clear, simple and easy to use.

no

does it have feathers?

other

soft lollies

vertebrates yes

Fig 6.5.1

Branching keys We have already looked at some branching keys. These are keys that get to a point and then branch off into smaller groups based on a choice made at that point. As stated earlier, a dichotomous key is one that branches off into only two groups at any point. Figures 6.5.1 and 6.5.2 are examples of a branching key and a dichotomous key.

Tabular keys

1

We have also looked at an example of a tabular key. These are also sometimes referred to as ‘go to’ keys. Like branching keys, the idea is to start at the top and work your way down, as shown in Figure 6.5.3.

has four legs doesn’t have four legs

go to 2 go to 3

2

Circular key

eats meat eats grass wears clothes doesn’t wear clothes

lion cow human go to 4

4

has wings doesn’t have wings

bee millipede

3

One type of key that we have not yet looked at is the circular key. With this type of key you start in the middle and work your way outwards. The circular key in Figure 6.5.4 can be used to distinguish between certain animals.

A tabular key to identify some animals

lion fish Indian elephant

African elephant funnel-web spider black can house kill spider can’t kill huntsman black spider body mainly green

fish

whale shark

eats le p peo

eat sn’t doe ople pe ous

h

s les

jaw

fis

hydra

hairy body

coral

multicoloured

extinct

tiger

sabre-toothed tiger

ly on

animals

i

can live on both land and water commonly found in Australia

not extinct

lives

not commonly found in Australia

Fig 6.5.3

tiger shark

in tilag car fish

only ater nw

mainly black

bony fish

elephant

spider redback spider

large striped small fins fins

small ears

lives on lan d

flower spider

big ears

bream

UNIT

6.5

cnidarian

jellyfish

poisonous

octopus

sea fan medusa polyp

box jellyfish sea anemone

blue-ringed octopus

not poisonous common octopus

Indian tiger

frog

Fig 6.5.4

salamander

This circular key helps identify some animals.

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More on keys Let’s say we wanted to use this key to identify the animal in Figure 6.5.5. We start in the middle, then move out to ‘lives in water’. After that we go to ‘fish’. From fish we go to ‘bony fish’. Then we go to ‘large striped fins’. This tells us the fish is a lionfish.

UNIT

6 .5

Classify this animal using the circular key in Figure 6.5.4.

Fig 6.5.5

[ Questions ]

Skills 1 Use the key in Figure 6.5.6 to classify these insects.

insects

large wings

2 Given a square, circle, triangle, oval and octagon, construct a branching key to classify them. 3 Choose five different types of chips that you know and construct a dichotomous key to classify them.

small or no wings

4 Choose ten pieces of laboratory equipment and construct a dichotomous key to classify them.

butterfly

5 Construct a tabular key to classify these people. shorter rear legs

very long rear legs

antennae in front of head

antennae to the rear

mosquito

grasshopper horned head

Fig 6.5.7

not horned head

rhino beetle

small eyes

large eyes

termite soldier

beetle

Fig 6.5.6

178

6 Use the following tabular key to classify the four cnidarians below.

1

branching arms

non-branching

go to 2

Heliastra heliopora

7 Use the following circular key to find out what type of (fictional!) animal this is. Fig 6.5.9

cara blip

UNIT

6. 5

disty

8 eyes

2 antennae

2 eyes

2

leaf-like arrangement

nodules (small lumps)

go to 3

Astraea pallida

yista

1 head

1 eye

2 heads

n ante o nna e

xero

animals

3 short stalk Gorgonia

feep

long stalk

6 legs 3 heads

4 heads

jooby

4 legs

din

b

yen

2 mouths

1 leg

Pennatula

1 mouth

no mouth

lip

zeep

a

8 Using the same key as in question 7, draw an example of an animal that could belong to each outer group.

c

9 Construct a circular key to classify these drinks. d

Fig 6.5.8

Fig 6.5.10

179

More on keys

10 Classify the plants shown below by constructing: a a dichotomous key b a tabular key c a circular key

180

>>> 11 Construct a key to classify items in one of the following sets. • all Rugby League jumpers • flags of at least ten different countries • a selection of stamps or coins Fig 6.5.11

Chapter review [ Summary questions ] 1 Identify one living thing and one non-living thing. List at least three characteristics of each in a table. 2 Identify five organisms. 3 Identify two examples of endothermic and ectothermic animals. 4 Clarify the term ‘excretion’. 5 Explain why we classify things. 6 The largest groups of organisms are called ‘kingdoms’. List the smaller groups in order. 7 Explain the term ‘species’ and give an example. 8 Explain what the binomial scientific name of an organism represents. 9 Identify the main groups of vertebrates and give an example of an animal in each group. 10 State the three main types of mammals. 11 Identify three groups of invertebrates and give two characteristics of each group. 12 Clarify the following terms: organism, stimulus, response, respiration, classification, phylum, taxonomy, vertebrate, exoskeleton, heterotroph.

[ Thinking questions ] 13 Both plants and animals use cellular respiration for energy. Explain why only plants undergo photosynthesis. 14 You accidentally touch a hot stove. Identify the stimulus and the reaction. 15 If you had a very large collection of music CDs, explain why it would be a good idea to invent a way of classifying them. 16 Explain an example from this chapter of how science ideas have changed over time. 17 Do you think all scientific ideas have changed over history? Identify and explain an example to support your answer. 18 Describe some evidence that supports the current five-kingdom system of classification.

[ Interpreting questions ] 21 You watch somebody running across a field being chased by a hungry lion. Identify which characteristics of life the person is showing. 22 You are standing by a campfire, listening to the rustle of the possums in the bushes, the crackle of the fire and the laughter of your friends. State whether all the things mentioned in this sentence are alive. Do any of the non-living things show any of the characteristics of life? Explain. 23 Dinosaurs are thought to have been reptiles. List the kinds of features you would expect them to have had if this is correct. 24 Some people believe that dinosaurs may have been warm-blooded. If this is true, explain what problems that would cause for their classification. 25 The first people to use the system of biological classification outlined in this chapter lived in north-west Europe. As more and more of the world became known to them, they had to change their system of classification. Can you explain why? 26 Imagine that you have spent a very long time studying the reptiles of Australia and have just published a book about them, containing a key to all the species. Explain the problems you would face if somebody discovered a new species of lizard in Australia. 27 Classify the following organisms in the animal kingdom. a dingo b red-bellied black snake c redback spider d kookaburra e platypus f kangaroo g Murray cod h yabbie i bat j sperm whale 28 Classify the following organisms in the plant kingdom. a apple tree b pine tree c tree fern d moss

19 Identify which technology used by scientists led to an increase in the number of kingdoms.

Worksheet 6.4 Classification crossword

20 Explain what a key is and why scientists use them.

Worksheet 6.5 Sci-words

181

Forces Key focus area:

4.3, 4.6.2, 4.6.7, 4.6.9, 4.6.10, 5.6.6

Outcomes

>>> The applications and uses of science By the end of this chapter you should be able to: describe what forces can do to an object describe what causes friction and identify situations where friction is an advantage or disadvantage use the terms ‘mass’ and ‘weight’ appropriately and recall the difference between them describe gravity in terms of its cause, and its effect on objects describe the forces that allow objects to float use the term ‘force field’ accurately and be able to sketch the field around a magnet

Pre quiz

identify what happens when poles of different magnets are placed near each other.

1 Form a sentence using the word ‘force’. What do you mean by the word ‘force’ in this sentence?

2 List four different ways you could get this science textbook to move on the desk that it is sitting on.

3 What is friction? 4 What’s the difference between mass and weight?

5 Describe two situations where forces are important.

6 Why must you wear a helmet whenever you ride a bike?

7

UNIT

context

7.1 We experience and use forces every day. Forces allow us to run, stand, write, open drink cans, and play sport. Riding a bike shows how forces can increase our enjoyment or if we take a fall, damage ourselves. If you fall, gravity pulls you down towards a heavy landing. The force of friction between you and the rough ground scrapes and cuts your elbows and knees. A bike helmet is the

only thing that protects your head from the force of impact on the hard ground. So what are these forces that can be great fun or can cause damage?

Introducing forces Scientists say a force is something that changes motion. This means that a force can: • get something to stop Example: You hitting the ground after falling off your bike. • get something going faster (called acceleration) Example: Your bike as it goes down a hill. • get something going slower (called deceleration) Example: As you put on your brake. • change the direction that something is travelling in Example: As you go around a corner. • twist or change the shape of something. Sometimes this change is permanent but often the object bounces back to its original shape. If this happens, we call the object elastic. Example: Your bike tyres squash and stretch as they go over bumps but return to their original shape. If you fall, your bones aren’t as elastic as tyres. They are unlikely to go back to their original shape, breaking or fracturing instead.

Contact and non-contact forces A force can be a push, a pull or a twist. Most forces actually touch the object they are pushing or pulling around. Some forces such as friction, air resistance and buoyancy are impossible to see but still touch the object that they are affecting. These forces are called contact forces because they touch the object. Other forces, caused by gravity, magnetism and electricity, are invisible and don’t touch the object

Forces in action

Fig 7.1.1

that they are affecting. These forces are non-contact forces. These forces act through a ‘force field’, and this does the pushing or pulling.

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Forces: what are they? How to draw forces

Fig 7.1.3

Springs can be used to measure forces.

Scientists draw forces using arrows. Arrows allow you to show both the direction and size of the force. The direction of the arrow shows the direction of the force. Long arrows show big forces and short arrows indicate small forces. NEWTONS 0 10

50

the ground pushes back on the bike

20

40 30

pedal force

air resistance

GRAMS 0 50 weight force

100

Fig 7.1.2

Forces are drawn as arrows, with the length showing the size of the force.

150

How to measure forces Have you ever pushed a spring to squash it or pulled it to make it longer? If you have, Prac 1 you would have found that the bigger the p.186 force you used, the more the spring was squashed or stretched. This fact gives us a way of measuring forces. If a pointer and a scale are attached to the spring, you can see how far the spring’s length has been changed. This is the principle on which a spring balance and most other scales work. All forces are measured in newtons, named after the English scientist, Sir Isaac Newton (1642 to 1727). The unit newton is abbreviated to N. An apple, for example, weighs about 1.5 N. Worksheet 7.1 Flight forces

184

Prac 2 p. 187

40

50

kg

60

UNIT

7.1

UNIT

7.1 [ Questions ]

Checkpoint Introducing forces 1 Copy and complete: A force is either a _____ or a _____ or a _____. 2 Copy the following and modify any incorrect statements so they become true. a Force is needed to change the direction of an object. b Things naturally slow down. No force is involved. c A force is required to change the shape of an object. d Objects speed up when they fall because there is a force involved. e Twisting is caused by a force. 3 List the things you would you look for to tell if a force is being applied to an object.

Contact and non-contact forces 4 Identify five forces that act through contact only. 5 Identify another three forces that act without any actual contact.

How to draw forces 6 Compare the size of a force shown as a long arrow with that of one shown as a short arrow.

How to measure forces

Think 9 Identify other words that mean the same as the terms ‘acceleration’ and ‘deceleration’. 10 Identify three examples of situations where there are: a push forces acting b pull forces acting 11 Identify three examples of situations where an object: a accelerates b decelerates or stops c changes direction d changes shape permanently e changes shape for a short time but then bounces back to its original shape

Analyse 12 Look at Figure 7.1.4 and identify the statement that best describes what the force is doing in each case. A B C D E F

starting movement or getting it to go faster stopping or slowing a moving object changing the direction of the object balancing another force, preventing movement changing the shape of an object causing a twist

7 State the unit used to measure forces.

>>

8 Identify the type of instrument that can be used to measure forces. What is the force doing?

Fig 7.1.4

185

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Forces: what are they?

13 Draw small, simple sketches of the following situations: • a weightlifter lifting a weight • a spanner tightening a nut • a nail being hammered • a small child pulling along a toy • a strong wind pushing your hair backwards • a sliding door opening • a football falling to the ground after it has been kicked a On each of your sketches, draw arrows to show the main forces. Indicate the size of the forces by using different length arrows. b Under each diagram, write words to describe the force as: • a push or a pull • contact or non-contact

d a car wreckage e wet mud f a diving board g a drinking glass 3 Examine a spring balance and explain how it works. Draw a simple diagram of its mechanism.

Surf 4 Find out more about what forces are by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 7, and clicking on the destinations button.

Project Roller ball

[ Extension] Investigate 1 ‘Elastic’ means that an object will bounce back to its original shape once a force is stopped. Other materials are called inelastic materials. Explain what inelastic materials do when a force is applied to them. 2 Classify the following as either elastic or inelastic materials: a an elastic band b a crumpled piece of paper c plasticine

UNIT

7.1

[ Practical activities ] Measuring forces

Prac 1 Unit 7.1

Aim To measure the force needed to do some common activities Equipment Spring balance

Method 1 Use a spring balance to measure the forces listed below. a Open and close different types of doors. b Pull off sticky tape stuck to a bench. c Pull your science textbook off the bench. d Lift or unzip your pencil case.

186

Your task is to build a structure that will allow a normalsized marble to drop a vertical height of 70 cm in as close to 20 seconds as possible: • Your structure must stand by itself and cannot be higher or longer than 70 cm. • The materials you can use are things that are readily available at home: cardboard boxes, tubing, plastic containers, glue, tape etc. • The marble must pass across/through a minimum of four different materials/structures. • You must label all forces that are involved in the trip: every push and pull.

e Undo a Velcro tab. f Open different types of drawers. 2 Some of the forces may change as you measure them. If so, write the smallest and largest measurements you take. We call this the range of measurements. 3 Note that some of the forces may be too large or too small for you to be able to measure.

Questions 1 Look carefully at your results. Explain what factors made some measurements very large. 2 List the forces in order from smallest to largest.

UNIT

7.1 Build your own force-measuring device Prac 2 Unit 7.1

Aim To build a simple force-measuring device using everyday materials

2 Place a mark on the scale with no masses. Mark it as zero (no force).

Equipment

3 Progressively add 50 g masses, marking the scale each time.

Materials as shown in Figure 7.1.5.

4 Since the scale is going to measure force, you will need to label the scale in newtons, not in grams. Use the table below to help you. This is called calibration of the scale.

Method 1 Build one of the following three designs:

5 Use the force measurer to re-measure some of the forces you measured in Prac 1. bosshead and clamp

cardboard

Mass added (g) 0 hacksaw blade or plastic ruler 50 g masses

retort stand

Equivalent weight force (N)

0

0

50

0.5

100

1.0

150

1.5

Questions 1 Clarify the meaning of the term ‘calibration’. Explain why calibration is important. wooden dowel

2 Compare your measurements in this prac with those taken in Prac 1. 3 Explain what happens to each of the designs when heavier objects are placed on them.

plastic graduated cylinder or measuring cylinder

markings on dowel

rubber band

coil spring metal washers

Fig 7.1.5

Three measuring device designs

187

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UNIT

context

7.2 Lots of things push and pull objects around. You can push your foot on the ground to increase the speed of your skateboard. You can pull on a rope in tug-of-war or on a zipper to close your fly. Gravity pulls all objects

downwards, making them fall, while buoyancy pushes objects up so they float. Friction slows a skateboarder down, and magnets move steel cans around in a recycling plant. These are all forces that you have seen or experienced.

There are two forces acting on you right now, and they are equal in size and opposite in direction. This means that they cancel each other out so there is no overall force on you. You are not moving, because the forces are balanced. Forces are balanced if they are equal in size but acting in opposite directions.

Fig 7.2.2 chair pushes back with the same size force as the weight force

weight force

Fig 7.2.1

Skateboarder pushing to gain speed

A balancing act What forces are acting on you right now while you are reading this book? First, there would be the downward pull of gravity (sometimes called weight). Even though you can’t see it, you know that gravity exists because if the chair broke you would fall down to the floor. You are not falling, however, because gravity is not the only force acting on you. The chair is also pushing you … upwards. You can feel its push through the pressure on your backside.

188

If forces in one direction are the same size as the forces in the opposite direction, they will balance. Forces are balanced on an object if it: • is not moving • is not getting faster or slower (we call this constant speed) • is not changing direction • is not changing shape. Worksheet 7.2 Skateboarding forces – the ollie

Prac 1 p. 190

7 In Figure 7.2.4 there are three objects that have no overall force on them. Copy these diagrams and add arrows to show how the forces cancel to provide no overall force.

Noah discovers the meaning of balancing forces.

UNIT

7. 2

UNIT

7.2

Fig 7.2.3 Balanced forces

[ Questions ]

Checkpoint A balancing act 1 Copy the following and modify any incorrect statements so they become true. a Forces are balanced when there is no overall force. b Forces are normally balanced when the forces are the same size and acting in the same direction. c If I am sitting on a chair, the only force on me is my weight force. d A car travels at constant speed when the force from the driving wheels balances the push backwards of the air (we call this air resistance) and friction between the road and the wheels. e A balanced force is needed if an object is going to accelerate. 2 Explain how you can tell if forces are balanced. 3 Describe what you would look for to check if forces are unbalanced. 4 Explain what will happen to a car moving at constant speed if all forces acting on it are balanced.

Analyse 5 Look around you. Identify three things that are stationary and have no overall force on them. 6 A bike is slowing down to a stop. Explain why the forces on it must be unbalanced.

Fig 7.2.4

8 Draw simple sketches of the following situations and add arrows to show the balanced forces involved: a A student is lying on a couch. b A student leans against the wall. c A person is standing. d A hang-glider floats in the air. e A skateboarder is cruising at constant speed along a footpath. f A drop of water hangs from a tap. 9 Draw simple sketches of the following situations and add arrows to show the unbalanced forces involved. (Remember that the length of the arrow indicates the size of the force.) a A student sits back on only two legs of a chair. b A parachutist jumps from a plane but hasn’t yet opened her chute. c A stone is dropped. d A passenger, not wearing a seatbelt, is involved in a car accident. e A parachutist is landing on the ground. 10 A class ran a tug-of-war. Who do you think would win in each of the following games? Provide a reason why you think that team won. a Three students went against another three students of equal strength. b Three went against four. c Ten students versus another ten students of equal strength. d Two versus ten.

189

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Balanced and unbalanced forces

[ Extension]

Challenge

1 The class tug-of-war continued. Who do you think would win these rounds and why? Fig 7.2.5 a

b

3 people

2 people

c

6 people 2 people

3 people

3 people

2 people

3 people

d 10 people

e 3 people

3 people

Wonky tower Construct as tall a structure as you can using no more than 20 drinking straws. The structure must be able to stand without any other support and must be able to hold a 50 g mass at its very top. You can cut straws and can use pins or glue to join the straws, but you are not allowed any other materials. 1 Each joint in the structure has forces acting on it. Are they balanced? Why? 2 What very important non-contact force is acting on the structure and the object?

10 people 5 people string washer

3 people pulley f

10 people

10 people clamp

1 person

benchtop

UNIT

7. 2

[ Practical activity ] Tug-of-war

Prac 1 Unit 7.2

mass

mass

Aim To examine balanced and unbalanced

a 3 masses

3 masses

forces

b 3 masses

4 masses

Equipment

c 4 masses

3 masses

Three pulleys and clamps, string/heavy cotton thread, metal washer/ring, 50 g masses

Method

3 masses

3 masses d

1 Set up the apparatus as shown in Figure 7.2.6.

3 masses

3 masses

2 Attach the masses shown and support them until they are all attached. 3 masses

3 Let all of the masses go at the same time.

f

4 Take note of any movement of the washer.

Questions 1 Record the situations in which the washer did not move. 2 Explain what this suggests about the forces on the washer. 3 State the situations in which the washer did move. 4 Explain why this suggests that the forces were not balanced.

190

2 masses e 3 masses

3 masses

3 masses

Tug-of-war

Fig 7.2.6

UNIT

context

7. 3 You use friction every day but probably don’t think about it. Imagine trying to walk if there was no grip or friction between your shoes and the floor. Imagine how fast you could go on your bike if there was no friction with the air or ground. There could also be problems if there were no friction between your brake pads and the wheel rim—the brakes wouldn’t work!

Introducing friction Friction is a force between two sliding or rolling objects that acts to slow the objects down. A bike will come to a stop if it is not peddled; your school bus will stop if the driver turns the engine off. In these two cases the force of friction will be greater than the force trying to keep the object moving—that is, the unbalanced Prac 1 forces will cause the bike or bus to slow p. 194 down and eventually stop. Friction is the force caused by the roughness of surfaces and always acts in the opposite direction to the object’s movement. What a drag! Some surfaces have a lot of When something moves through air it needs to push friction because they are very the air out of the way and rough. If we try to slide one then around it. The air ce rough surface over another, passing over the surfa has its own friction force, the bumps and hollows catch called air resistance or on each other and slow it drag. Cars and commercial to down. aircraft are designed save to drag the ise minim Smooth surfaces have on fuel consumption, and bumps and hollows jet fighters and arrows are too, although their as designed to travel as fast possible. An object is ‘roughness’ can called streamlined if it cuts often only be through the air with little air seen under a Prac 2 resistance or drag. p. 195 microscope.

Fig 7.3.1

Even smooth surfaces have bumps and hollows—an electron microscope view of the surface of a plastic contact lens.

motion

friction

Friction is always opposite to the direction of motion.

Fig 7.3.2

Friction can also wear away parts of a surface— remember what happens when you fall onto the gravel or asphalt. This can also be a problem in machines, since their parts will gradually wear out with time. The wheels and peddles on bikes and the wheels on skateboards all have parts moving across

191

Friction: slowing down and getting moving other parts. These metal or rubber parts will gradually lose their sharp edges, become smaller or thinner and eventually fail. Friction also causes heat to be generated. We rub our hands together on cold mornings because we can generate heat by friction.

>>> the ground. This way the hovercraft can travel over extremely rough surfaces (ground or water) without slowing down because of friction. A hovercraft uses a blanket of air to reduce friction.

Fig 7.3.4

Reducing friction We would travel further and faster, and machines would be more efficient, if we could reduce the friction between their moving parts. There are a number of easy ways of reducing friction. Friction occurs because of the roughness of the surfaces that try to slide over one another. If the hollows are filled in, the surfaces become smoother and will slide over each other much more easily. This happens when the surface is lubricated with oil or grease. Polishing and waxing make the surface smoother by removing some of the bumps and filling up some of those hollows that catch and cause friction. Wheels, rollers or ball bearings also reduce friction. Ball bearings allow your skateboard or inline skates to roll more freely by reducing the friction, allowing you to go as quickly as possible.

Fig 7.3.3

There is less friction if wheels spin on bearings.

The most effective way of reducing friction is to stop the surfaces touching each other at all. A hovercraft does this by squeezing a blanket of air underneath it so that the craft loses contact with

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Useful friction So far, friction seems to be a problem force. But friction can work for us too. On your bike, you need to make sure the brakes are in good condition so that the friction of the brake pads against the rim is high. The condition of the tyres also contributes to the safe operation of the bike, as friction between the tyres and the road allows the bike to go forward and around corners. The type of tyres is also of great importance when the ground is rough and loose. Mountain bikes use a wider, blocked tread to gain more grip, as shown in Figure 7.3.5.

Fig 7.3.5

Mountain bike tread

What happens to a car that is trying to move on an icy road? Its wheels spin but does the car move? Can it be controlled once it is in a skid? When we try to move forward, whether we are in a car, on a skateboard or walking, we need to push backwards.

If the surface is rough, friction pushes back against our foot and pushes us forward. We get traction and traction moves us forward. If the surface is smooth then we lose traction: we simply cannot get moving or control our movements and we slide and skid. We have nothing to ‘push off’.

UNIT

7.3

Useful friction 4 Clarify the term ‘traction’. 5 Friction allows us to do many things. List at least ten situations in order from greatest frictional force to least. 6 Identify a device that needs friction to work.

Think 7 State five examples of objects that naturally slow down (or stop) because of friction. 8 State five examples of surfaces that have very little friction between them.

the ground pushes back on the skateboard and it moves forward

you push the ground backwards

We need friction between our foot and the ground to move forward.

UNIT

7. 3

9 Friction makes hinges on a door squeak, allows us to write with a pencil and to file our nails. Explain each of these situations using scientific terms. 10 A snowboarder hates friction but a cyclist is happy it’s there. Explain why. Fig 7.3.6

[ Questions ]

Checkpoint Introducing friction 1 Copy and complete: Friction is a force caused when two surfaces … 2 Copy the following and modify any incorrect statements so they become true. a Friction is caused by bumps and hollows of the surfaces catching on each other. b Smooth surfaces have no bumps or hollows. c Friction causes a moving object to speed up. d Friction is a non-contact force. e Drag slows a moving object. f ‘Streamlined’ is a word used to describe shapes that cut through the air easily.

Reducing friction

11 List three machines or devices that would benefit from using bearings in their wheels.

Analyse 12 In a world without friction, predict what would happen to: a objects that you hold on to. b pieces of wood nailed together. c pieces of wood screwed together. d your doona or blankets through the night. e your shoelaces. f the way you move across a room. g the way you stop. 13 List the disadvantages of friction as a force. 14 Predict the order from most to least friction for the blocks in Figure 7.3.7. Fig 7.3.7

A

B long round dowels

C oil

3 Construct a table to summarise the different ways that friction can be reduced.

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Friction: slowing down and getting moving

[ Extension] Investigate

Surf

1 Investigate why weightlifters put chalk on their hands when attempting a heavy lift. What other sports use chalk to assist the participant? 2 Investigate why snowboarders wax their boards. Find other sports where this happens.

7 Find out more about the forces involved in skateboarding by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 7, and clicking on the destinations button.

3 Car brakes get hot after driving in the city. Investigate how disc and drum brakes work. List the advantages that disc brakes have over drum brakes.

Creative writing

4 The tread on car tyres helps to increase friction or ‘grip’ in wet conditions. When conditions are dry, the tread actually reduces friction: in these conditions, racing cars put on ‘slicks’ with no tread. Explain why tread is only important in the wet. 5 When we drive in snow, we often are required to put chains on our tyres. Research why.

Create 6 How did the gangs of slaves in ancient Egypt move the massive blocks of stone across the desert to build the pyramids and temples? Construct a model demonstrating how you think these large blocks were shifted over the sand.

UNIT

7. 3

Overnight scientists have discovered that friction has disappeared! What can we expect today in this new, frictionless world? Create a short piece of writing on friction. You must explain: 1 what friction is 2 how you intend to move about and stop 3 what will happen to structures (will nails hold and screws stay in?). • •

Write your piece as either: a diary page about your exploits after getting out of bed a newspaper front page explaining what is happening in the world

or • a pamphlet from the government explaining to residents how to cope in this strange new world.

[ Practical activities ] Bumps and hollows

Bumps and hollows Prac 1 Unit 7.3

Aim To investigate the smoothness of surfaces tape

Equipment 2 x A4 sheets of paper, light cotton line or fine string, sticky tape

tape

string

tape

tape

Method 1 Tape a piece of A4 paper to the bench to hold it in place. 2 Tape 30 cm of cotton line to the edge of the other piece of paper.

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Fig 7.3.8

>>

tape tape

string

tape

3 Use the cotton line to pull the top sheet across the bottom one.

Bottom sheet

Top sheet

4 Now carefully fold the top sheet as a concertina, as shown in Figure 7.3.8.

Smooth

Smooth

5 Repeat the experiment with both sheets folded as a concertina.

Smooth

Folded

Folded

Folded

UNIT

7.3 Observations: was the task easy, hard or impossible?

6 Record your observations in the table.

Question Write a statement about what makes it difficult to slide things over each other.

Measuring friction Prac 2 Unit 7.3

Aim To compare the friction of different materials on a surface

Fig 7.3.9

One way to compare frictions

Equipment

Protractor, wooden blocks, selection of different materials (bare wood, carpet, various grades of sandpaper, rubber grip material), ‘ramp’, lubricants such as detergent, non-stick spray, cooking oil, wooden dowels etc

wooden block

ramp

material to be tested

Method 1 Construct a table in your workbook with the following headings:

protractor 90

benchtop

Material

Angle

2 Predict which material would have the least friction and which would have the most. Arrange them in order in the table. 3 Place a wooden block on the wooden ramp. 4 Slowly lift one end of the wooden ramp until the block is just about to slide. 5 Measure the angle between the ramp and the desk with a protractor. 6 Place one of the selected materials on the ramp and repeat the experiment. 7 Repeat with all the other materials.

Extension 8 Repeat the experiment, but this time lubricate the surface instead of making it rougher. 9 Run another experiment, placing the block on wooden dowels to act as ball bearings.

Questions 1 What happened to the angle as you changed the roughness of the surface? 2 Explain your answer in terms of friction.

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UNIT

context

7. 4 You’re on your bike travelling along at high speed when you unexpectedly hit a rock. You lose control, and as the bike flies out from under you there is only one way to go— down! You have to love gravity.

Introducing gravity Gravitational force is a non-contact force that attracts objects to each other. In the above example you are attracted to the ground. Although normally a very small force, gravity becomes significant when we are near a large object such as a planet like Earth, a moon or a star like the Sun.

Fig 7.4.1

I find you attractive! Building on the earlier work of Galileo and Johannes Kepler, Sir Isaac Newton in 1687 developed the law of gravitation. This law suggests that all things with matter are attracted to all other things with matter. This means that you are currently being pulled towards the desk in front of you … and the person sitting next to you … and the ceiling … and everything else in the room! It sounds like some sort of nightmare until we realise that the gravitational force is actually extremely small, so small that most things do not affect us.

American astronaut Ed White is weightless in space. Does he still have mass?

In effect, gravity makes things fall down. Of course, ‘down’ depends on where we are on Earth!

Mass

Prac 1 p. 200

Mass is the amount of matter in an object. Unless we break the object up or add things to it, the mass of an object never changes. That’s massive! Astronauts, for example, can A Boeing 747-400 (the ‘jumbo’) flies non-stop be ‘weightless’ in space, but from Sydney to Los Angeles their body mass has not every day using almost all changed. its 173 000 kg of fuel on its 14-hour, 13 000 km Mass is normally measured journ ey. On take off, its in kilograms (kg), maximum mass (aircraft, but sometimes is measured in passengers, cargo and fuel) is 400 000 kg. This is the grams (g) for smaller things, equivalent of 258 Holden or tonnes (t) for very large Commodores! objects. We often use the terms ‘mass’ and ‘weight’ interchangeably in everyday speech. They are, however, different things.

Weight Weight is the name given to the pulling force on a mass caused by gravity. Weight is a force and depends on two things: • the mass of an object • the gravity on the object. To find the weight of an object you multiply its mass by gravity: Weight = mass x gravity W =m x g

On Earth, gravity is about 10 m/s2, and therefore you would need a force greater than 10 newtons to lift a 1-kilogram mass. Like all other forces, weight is measured in newtons (N). Worksheet 7.3 Pressure

196

The effect of distance Gravity gets smaller as you get further away from Earth. This is because gravity depends on distance. This may seem strange since our weight doesn’t seem to get any smaller if we climb a mountain. This is because you have to go much further away than that for the decrease in gravity to be noticeable. A 70 kg person normally has a weight of about 700 N (exactly 686 N) at sea level. The table shows what happens to the person’s weight as they travel to the Moon.

Distance from Earth’s surface

What is normally found at this height

Mass (kg) Weight (N)

0

Sea level

70

686.0

305 m

Top of Centrepoint tower

70

685.8

2228 m

Top of Mt Kosciusko

70

685.5

10 km

Normal height of commercial airliners

70

683.8

395 km

Height of space station

70

608.3

595 km

Hubble space telescope

70

573.9

35 900 km

Aussat 2 communications satellite

70

15.4

190 000 km

Half-way to the Moon

70

0.8

Gravity and weight get less as we go further away from the Earth.

UNIT

7. 4

Fig 7.4.2

70 kg 0.8 N

Aussat 2 communications satellite 36 000 km 70 kg 574 N Space station 400 km

70 kg 15 N

Commercial aircraft 10 km

70 kg 608 N

70 kg 686 N 70 kg 683.8 N

Earth

Hubble space telescope 600 km

2 km 70 kg 685.5

Measuring mass and weight Mass can only be measured by using a balance. If the two sides of the balance are the same, then the mass on both sides is equal. This would be the case whichever planet you were on, whether it was Earth, the Moon or Mars.

Because weight is a force due to gravity, you must use gravity to measure it. You allow gravity to stretch or squash a spring to give you a measurement.

Prac 2 p. 200

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Gravity

5 Identify the direction in which the weight force is pointing. 0

100

200

300

400

500

600

0

10

20

30

40

50

60

70

80

90

100

1

2

3

4

5

6

7

8

9

10

0

6 Weight depends on two things. State what they are. 7 Distinguish between mass and weight.

Think 8 Copy and complete: All things fall at the _____ rate unless _____. 9 Explain how mass and weight can be measured. 10 Clarify the term ‘weightlessness’. 11 In space, does an astronaut have less mass or weight? Explain. 12 The following comment was overheard in a Year 7 class recently: ‘Of course 1 kg of lead is heavier than 1 kg of feathers! It’s lead, isn’t it?’ Explain why the student has got it wrong and how they may have come to have this opinion. 50 40 20 10 0

A beam balance (top) measures mass, a spring balance (bottom) measures weight.

UNIT

7. 4

Fig 7.4.3

[ Questions ]

Checkpoint Introducing gravity 1 Clarify the term ‘gravity’.

Mass 2 Clarify the term ‘mass’. 3 State common units that are used to measure mass.

Weight 4 Identify whether weight is: a a push force or a pull force b a contact or non-contact force

198

13 Copy the following and modify any incorrect statements so they become true. a Weight is measured in grams. b Kilogram is a unit for mass. c Weight is a force. d The weight of an object is the same everywhere you go. e Gravity does not depend on how far you are from a planet. f There is no gravity on the Moon. 14 List the three things gravity depends on. 15 Identify where on Earth you think gravity would be the greatest and where the least. 16 ‘All things fall at the same rate due to gravity.’ a State one observation that supports this statement. b State an observation that does not support this statement.

Analyse 17 The gravity on the Moon is only one-sixth the gravity on Earth. Explain what this suggests about the mass of the Moon. 18 List three activities you could do on the Moon that on Earth you normally would find difficult.

19 Three balls—a tennis ball, a cricket ball and a shotput — were dropped at the same time. The experiment was photographed on the way down, but unfortunately only the tennis ball was recorded on film. Complete the ‘photographs’ by predicting where the other objects would be at the same time as the tennis ball. Fig 7.4.4 tennis ball

Where will the others be?

cricket ball

shot put

2 Research and record the world records for: a the largest mass that a man and a woman have lifted b the heaviest thing living at this moment c the smallest living thing d the heaviest of the dinosaurs e the heaviest ship ever built

UNIT

7. 4

3 Investigate how gravity keeps planets such as Earth revolving around the Sun and the Moon revolving around the Earth. 4 In science fiction movies, you often hear of a spacecraft being ‘caught’ in the gravitational field of a planet. NASA often does this to change the direction of its deep space missions. Investigate how NASA does this.

Creative writing Skills 20 An astronaut has a mass of 75 kg. Calculate his weight on earth if gravity is 10 m/s2. 21 Calculate your weight using your own mass, if gravity is 10 m/s2. 22 Complete the following table using the formula for weight: weight = mass x gravity

Weight

Mass

Gravity

5 kg

10 m/s2

2 kg

10 m/s2 10 m/s2

10 N 20 N

Imagine a world without gravity. Nothing would fall down. Create a piece of writing about a world without gravity. You can produce either: • a pamphlet for umpires explaining the rules of a sport invented for a world without gravity • a diagram or model of a gravity-free home, bathroom or toilet • a set of rules for going to bed without gravity and a design for the bed or • a poster of exercises to keep astronauts fit and to stop their muscles getting weaker while on long space missions.

2 kg

Project

10 m/s2

14 N 100 g

10 m/s2

[ Extension] Investigate 1 Research and record the masses in kilograms of: a an average adult man and woman b an average newborn baby c an average family car

Strength Find the stretch and strength of one of the DYO following objects: • a plastic supermarket bag • sticky tape • a nylon fishing line • an elastic band. You are to draw a line graph of the stretch obtained as the masses were added. Mark clearly the mass required to break the object.

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Gravity

UNIT

7. 4

[ Practical activities ] Falling objects Aim To see if all objects fall at the same speed

Prac 1 Unit 7.4

Equipment 50 g mass, a range of different objects that will not break if dropped

Method 1 Collect a range of objects of different masses and different shapes and sizes. 2 Drop the 50 g mass and one of the other objects at the same time from the same height. Ensure that the objects fall onto something soft so as to reduce any damage. 3 Make the drop as high as possible. 4 Repeat with all the objects, until you have compared every object with the drop of the 50 g mass. 5 Arrange the objects in the following table: A lot faster than the 50 g mass

About the same as the 50 g mass

A lot slower than the 50 g mass

9 Drop the 50 g mass and the paper ball and record your results again. 10 Crumple the paper into a very tight ball and repeat the experiment.

Questions 1 Identify the column in which you placed most of the objects. 2 Identify the type of objects that ‘fluttered’ on the way down. 3 Explain why you think they did that. 4 Identify whether any masses fell faster than the 50 g mass. If so, Explain why. 5 Complete this sentence: Most objects fall at the same rate as/faster than/slower than a 50 g mass. Objects that ‘flutter’ instead of dropping

6 Describe the only difference between the sheet of paper, the loosely crumpled ball and the tight ball. 7 Identify which dropped slowest. Explain why.

6 Now drop the 50 g mass and a single sheet of A4 paper at the same time and from the same height. 7 Add these results to the table.

8 Draw a conclusion by completing these sentences: Objects that catch the air fall ______ than objects that do not. Objects that do not catch air fall ______.

8 Now crumple the paper into a loose ball.

Measuring mass and weight Prac 2 Unit 7.4

Object

Mass measured from beam balance (g)

Weight measured from spring balance (N)

Aim To accurately use a beam balance and spring balance to find the mass and weight of different objects

Equipment Beam balance, spring balance, a variety of objects of different weights and sizes

Questions

Method

1 State the maximum mass that could be recorded using the beam balance.

1 Use the beam balance to measure the mass of each of the objects. 2 Now use the spring balance to measure the weight of each object. 3 Record all your measurements in a table like the one opposite.

200

2 State the maximum weight that could be recorded using the spring balance. 3 Copy and complete: The weight of an object was about _____ times the mass of the object.

Science focus: Flying high Prescribed focus area: The applications and uses of science An understanding of forces has allowed humans to create a wide variety of useful machines and activities that were previously impossible. An interesting example of this is humans’ attempt to fly. Shortly after learning how to fly, humans again used their knowledge of forces to allow them to jump out of the aeroplane and land safely. Others considered the possibilities of going even higher and faster to eventually travel into space. Today there are many forms of flying machines and ongoing research to try and improve them.

How wings create lift Two inventions have made it possible for humans to fly. The first is the wing, or aerofoil. The second is engines that produce enough force to reach very high speeds. The speed is needed to allow the air moving over the wings to create lift. The lift overcomes the weight-force due to gravity and the aeroplane can take off. The forces acting on an aeroplane wing when flying at a constant speed and altitude are shown in Figure SF7.1.

Air above the wing rushes across the upper surface of the wing to catch up with the air travelling below the wing Lift

This fast-moving air creates a LOW PRESSURE compared to the air under the wing.

Thrust

Drag

Front of wing is pushed through air.

Weight Air on the underside of the wing moves more slowly. This slowly moving air is at HIGH PRESSURE compared to the faster-moving air above the wing.

Motion Airflow

Fig SF7.1

A wing showing forces at constant speed and altitude

The thrust is provided by the aeroplane’s propeller or jet engine. The drag is due to air resistance as the aeroplane pushes through it. Air resistance is caused by the molecules of air colliding with the moving object. The lift is produced because the air across the top of the wing has to travel further, so it moves faster to catch up with the air travelling under the wing, and is more spaced out. This makes low pressure air above the wing. The air underneath the wing has less distance to travel, so moves more slowly. This makes it less spaced out and higher pressure. The wing gets sucked up into the area of low pressure. The weight is due to the mass of the aeroplane being pulled down by the Earth's gravity. The lift must be greater than the weight for an aeroplane to take off.

Faster and higher When scientists thought about going faster and higher, they knew that wings could only produce lift when there is enough air. This means that to leave the Earth and fly into space, a new engine and craft would be needed that did not have wings. This led to the rocket engine. Rockets must overcome gravity and air resistance to fly into space and this requires lots of energy. This means a rocket must be very powerful and produce enough thrust to propel the spacecraft through and out of the Earth’s atmosphere. Unfortunately, rockets must carry all their fuel, so most of the energy needed to lift a rocket into space is wasted on carrying the fuel. The space shuttle is much smaller than the huge fuel tanks it carries. Once in space, a smaller rocket engine can produce the thrust for the spacecraft as there is no air resistance, and gravity is much less. Research is continuing to develop new engines that will more efficiently transport spacecraft and satellites into orbit. It is hoped that these new engines will also be used for aeroplanes to allow us to travel faster than ever before. Imagine a jet engine that doesn’t pollute te atmosphere, flies at seven times the speed of sound and doesn’t carry any fuel. Well, Australia is a leader in this area, with Queensland

201

Jump!

Fig SF7.2

1 When the skydiver first jumps from the aeroplane they are pulled down by Earth’s gravity. Their speed is low, so air friction is small. The skydiver accelerates downward, gaining speed.

Air friction Speeding up Weight-force (due to gravity)

Air friction at high speed

2 The skydiver continues to gain speed and the air friction increases. When they are travelling very fast, the air friction pushing them up becomes equal to gravity pulling them down. This means the forces are balanced and the skydiver no longer accelerates, but continues to fall at a constant speed. This speed is known ‘terminal velocity’.

3 The moment the skydiver opens their parachute, the air friction increases greatly as more air molecules collide with the parachute. Air resistance is now far larger than gravity. This causes the skydiver to slow down until air friction pushing upwards once again becomes equal to the weight pulling downwards. Fortunately for the skydiver, this is at a much slower speed than when they first opened their chute.

Terminal velocity

Weight-force (due to gravity)

Air friction at high speed when parachute opens

Slowing down

Weight-force (due to gravity)

University doing research into a new form of propulsion system called a scramjet (super sonic scramjet). The scramjet is a more efficient engine as it uses oxygen from the air, and does not have to carry much fuel. The Australian team, working on a

202

shoestring budget, have shown great innovation and creativity to make good progress. In 2002 they conducted a successful trial of the scramjet, known as HyShot, using a rocket launched from Woomera. The scramjet project is supported by NASA and many other sponsors.

Enormous rockets are used to propel the space shuttle through Earth’s lower atmosphere and into orbit.

Fig SF7.3

Fig SF7.4

Launch of a HyShot rocket from Woomera, carrying an experimental scramjet engine being developed by Queensland University

[ Student activities ] 1 Many objects are caused to move, change direction, speed up, slow down or stop due to forces acting on them.

• large helicopter • small military jet • large commercial jets.

a In small groups create two lists. i Methods or devices that use forces to get objects moving. ii Methods or devices that use forces to control the motion of an object, or stop it moving. b For each of the devices in your list, write a short description of how they use forces and attempt to name the forces involved. 2 Draw an aeroplane wing and include arrows on your diagram to demonstrate the size and direction of forces in the following situations: a during take-off b accelerating at a constant altitude c just before touchdown

Try to find out which aeroplanes fly highest in the atmosphere.

3 Because most flying machines require air to operate, they are restricted to flying at particular heights. Research the maximum height that can be safely reached for the following flying machines: • small helicopter • small propeller-driven aeroplane

Record your information in a table. 4 a Investigate the forces produced by a rocket. b Use a series of diagrams to create an information brochure demonstrating how a rocket engine works. Make sure you show the forces acting on the rocket. c Build a working model rocket. Try using a film canister, Alka-Seltzer tablets and water. You will find many examples on the Internet. 5 Australia was once among the leaders in rocket science and one of the first to launch a satellite into orbit around the Earth. Complete one of the following activities. a Research and describe how an understanding of forces now makes it possible to place a satellite in a stable orbit around the Earth. b Investigate and record any major contributions made by Australia to producing new forms of propulsion systems. Be sure to include some information on the Queensland University work on the scramjet.

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UNIT

context

7. 5 There are two special forces involved when objects are placed in water. The force that allows you to sit on your surfboard and float while waiting to catch a wave is known as buoyancy. The other force, called surface tension, allows you fill a glass above the rim without it spilling Prac 1 and enables some insects to walk on water. p. 206

buoyancy

Buoyancy A lump of steel sinks if it is placed in water, yet a ship made from steel floats. How is this possible? This is because the ship’s weight is balanced by the

weight

Fig 7.5.2

Weight is greater than buoyancy.

water pushing upwards on its hull. The Prac 2 force that keeps the ship from sinking is p. 206 called buoyancy. A ship would definitely sink if it were solid steel: steel is more dense than water, so it sinks. The hull is hollow, however, and contains air, making the ship less dense than the water it floats in. Water gives the ship its upward buoyancy force, which then balances the downward weight force of the ship. As the ship is loaded, it gets lower and lower in the Dead man’s float water. If it is loaded too If we want to float in much, or if the hull is holed a pool we always breathe in, filling and fills with water, it will our lungs with air. If we get sink. The buoyancy force is rid of all the air, we wil l generally sink: the bu now not enough to balance oyancy is now not enough to the weight of the ship, and keep us afloat. down the ship will go.

buoyancy

weight

Surface tension

Buoyancy equals weight-force.

204

Fig 7.5.1

Water creates a ‘film’ or ‘skin’ on its surface. This skin is often strong enough to keep afloat objects that would normally sink and can make water take on shapes that are quite unexpected.

Prac 3 p. 207

UNIT

7. 5 All water particles have, between them, a force of attraction, called cohesion. This holds the water particles together. Cohesion at the surface is called surface tension and is sometimes strong enough to form a ‘skin’. Drops of water can hang from a tap without falling, we can fill a glass above the lip and small insects can walk on water because of the ‘skin’ that surface tension creates. Worksheet 7.4 A paper boat

UNIT

7. 5

[ Questions ]

Checkpoint Buoyancy 1 Copy the following, correcting any incorrect statements so they become true. a Gravity is the force that keeps a ship afloat. b An iceberg stays afloat because its buoyancy balances its weight force. c A ship will sink if its weight is greater than its buoyancy. d Small objects often float because they are very dense. 2 Explain the term ‘buoyancy’ in your own words.

Surface tension 3 Explain what cohesion is. 4 State what cohesion at a surface is called. 5 Identify what this cohesion at the surface forms. 6 List three places where you have seen surface tension in action.

Fig 7.5.3

Surface tension being used by a pond skater

Analyse 10 Plimsoll lines are lines painted on the hull of a ship to show where the waterline should be under different conditions. Below is a diagram of a partly loaded ship. Copy this diagram and draw and label Plimsoll lines for: a when the ship is empty b when the ship is fully loaded c a safe line for a ship expecting heavy and dangerous seas. Fig 7.5.4

Plimsoll lines on a container ship

Think 7 Organise this list into a table that classifies the following objects into those that float on water and those that sink. a a small pebble b a house key c a paperclip d a cork e a drop of car oil and a drop of cooking oil f a cricket ball g a book and a sheet of paper h an ice cube i a leaf j an inflated balloon and a deflated balloon

LT LS LW LWNA

LTF LF L

TF F R

T S W W

8 Explain what density has to do with buoyancy.

11 How does a steel submarine float on top of the water while it is in harbour?

9 What happens to the water level on a ship as it is loaded? Explain.

12 When out at sea, the submarine dives. Explain what the crew must do to allow it to dive.

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Forces in water

[ Extension] Investigate

Create

1 It is impossible for a person to sink in the Dead Sea on the Israeli/Jordanian/Palestinian border. It is also recommended that people with small cuts or open wounds do not swim there because it would be very painful for them. Investigate what is strange about the Dead Sea that could account for these two facts.

3 Using a sheet of A4 paper (or a piece of aluminium foil of the same size), design and build a ‘boat’ that can hold the greatest number of paperclips. Run a competition between class members to find out who has the best boat.

2 When a piece of newspaper is dropped in water, it will probably float, but after a while it will sink. Examine this phenomenon and explain what is happening.

UNIT

7. 5 Prac 1 Unit 7.5

[ Practical activities ] What water does

How do ships float?

Aim To investigate buoyancy and surface tension

Aim To investigate the principle of buoyancy

Equipment Table tennis ball, balloon, bucket/pneumatic trough/large sink, thin test tube, bubble-making equipment, detergents, glycol

Prac 2 Unit 7.5

Method 1 Try to hold a table tennis ball under water and an inflated balloon under water.

Equipment 100 mL conical flask, a large container such as an plastic ice-cream container or bucket, spring balance, elastic band, cork or rubber stopper

Method 1 Copy the table below into your workbooks.

2 Observe a drop of water hanging from a tap and a small amount of water on the bench.

Observations as flask is lowered into water

3 Observe the top of the water in a half-filled test tube and a test tube filled until it is brimming. 4 Make some bubbles using various detergents and glycol mixtures. Determine which mixture was the best in making the largest bubbles. 5 Carefully draw diagrams of each situation.

Weight of flask as it is lowered (N) into water

Empty flask Quarter-full Half-full

Questions 1 Identify each case as an example of either buoyancy or surface tension at work. 2 Propose two ways each in which surface tension and buoyancy may be useful.

2 Seal the empty flask with the cork/rubber stopper. 3 Place an elastic band tightly around the neck of the conical flask. Use it to attach the hook of the spring balance. 4 Weigh the sealed conical flask. 5 Lower the conical flask into a large container of water.

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206

Fig 7.5.5

How does a ship float?

6 Record your observation of what is happening to both the flask and the reading on the spring balance.

UNIT

7. 5 7 Progressively add more water to the flask and repeat the above.

spring balance 50 40

Questions

20 10 0

1 State the weight of the empty flask in air. elastic band/string water

2 Describe what you noticed about the flask’s weight as it was lowered into the beaker of water. Explain.

stopper flask

3 Draw a diagram of all the forces on the flask as it was lowered into the beaker of water. ice-cream container filled with water

4 State how full the flask was when it just sank. 5 Explain why the buoyancy force is sometimes insufficient to keep objects afloat.

2 Carefully place a pin on the surface of the water. Record what happens.

A special case of floating Prac 3 Unit 7.5

Aim To examine the forces involved in surface tension

4 Place your eye level with the surface of the beaker and draw what you see. 5 Carefully rest a pin on the edge of the beaker and see if you can get the other end to float on top of the water.

Equipment Two fine pins, 250 mL beaker, detergent, eyedropper, aluminium tray, milk, food colouring

Method 1 Fill the 250 mL beaker with water until it nearly reaches the top. Fig 7.5.6

3 Now add more water very slowly and carefully until it is brimming—that is, the water is actually above the lip of the beaker.

How to make a pin float

6 If you cannot make it float, carefully use another pin to push it into the centre of the beaker. Keep trying if at first you don’t succeed. 7 Record your observations of the water around the pin. 8 Repeat the experiment but now place a small amount of washing detergent on the surface. Record your observations and explain the effect of the detergent. 9 Place a mixture of milk and water into an aluminium tray to cover the base. 10 Allow it to settle, then place one drop of food colouring in the centre of the milk. Using an eyedropper place a single drop of detergent in the middle of the food colouring. 11 Observe and record what happens.

Questions 250 mL

1 A pin normally drops to the bottom of a beaker of water. Explain why. 2 With care, the pin floats. Use the idea of surface tension to explain why. 3 If pushed too hard, the pin once again sinks. Explain what has happened to the surface tension now. 4 For the milk experiment, use surface tension to explain the effect the detergent had on the food colouring.

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UNIT

7. 6 context

Which direction do we go?

Magnets exert an invisible force that is strong enough to push or pull without even touching. This force is called a magnetic force. It is a non-contact force that has many uses. You would have felt the pull of a cupboard door just before it closes, or the pull of the rubber magnets that are on the fridge door. These magnetic forces attract only over a short distance between the magnet and the metal.

Introducing magnets Magnets can: • attract metals containing the elements iron, nickel or cobalt. Steel is a common metal which contains a high percentage of iron. Magnets therefore also attract steel. • pull the ends of other magnets towards them (attract), or push the ends of those same magnets away (repel) Iron filings in the magnetic field of a bar magnet

• point to the north and south poles of the Earth • make some other objects magnetic.

It is thought that birds, turtles and even bees may use the magnetic fiel d of the Earth to navigate while travelling over long distances.

Attraction and repulsion The magnetic force fields are particularly strong at the ends of a magnet. The ends are called poles: the north pole and the south pole. Poles that are the same (called like poles) push away or repel each other. Poles that are different (unlike) pull Prac 1 p. 211 together or attract each other.

Fig 7.6.1

Magnetic like poles repel (top), magnetic unlike poles attract (bottom).

208

Fig 7.6.2

Making and destroying magnets The first magnets were simply lumps of rock that were naturally magnetic. These rocks contained a lot of iron and were called magnetite or lodestones. Magnets, iron and steel are all thought to have inside them mini-magnetic particles called domains. In unmagnetised iron, these domains are pointing in different directions. The forces from these minimagnets cancel each other out and give no overall magnetism. If another magnet is used to push these domains around, they can become aligned and the piece of iron will become magnetic. This process is shown in Figure 7.6.3.

S

Bar magnet showing the force field with small compasses

N

N

S

N

S

S

S

N N

N

N

S

N

S

N

S

N

S

N

S

N

S

N

S

N

S

N

S

N

N

S

N

S

N

S

Fig 7.6.3

Fig 7.6.4

N

S N

S

S

S

S

N

would point in the field. Scientists show the direction of the field with arrows that point away from the north pole and into the south pole.

UNIT

7. 6

Iron becomes magnetic if its domains align.

This can be done by: • stroking the piece of iron or steel repeatedly, in the same direction, with another magnet • lining up a piece of iron with the north and south poles of the Earth and gently tapping it • leaving the iron in the core of an electromagnet. If magnets are dropped, hit or heated, the domains can be knocked out of alignment and the magnetism is lost. Permanent magnets are made from harder steel or cast iron where the domains are more resistant Prac 2 p. 212 to being knocked.

Magnetic fields Non-contact forces must have a method of moving other objects without touching them. This happens because there is a force field around the magnet. This magnetic field is the area around a magnet where a magnetic force is felt. Magnetic field lines show the direction an iron filing or a compass needle

These lines never cross and come straight out of any surface. Lines that are close together show strong fields. Weak fields have their lines widely spaced. Magnetic fields are strongest at the magnet’s poles and get weaker as we move Prac 3 p. 212 further away from them.

Magnetic Earth The ancient Chinese, Romans and Greeks all used lodestone (a natural magnetic rock) as a primitive compass to help them in their navigation. Although used less now than in the past, compasses are still used in navigation. Compasses are actually small magnets that are allowed to move. The compass needle aligns itself with the Earth’s Watch it! field lines and can be used to The fine inner workings find north or south. of a watch can easily be destroyed if a strong This suggests that the magnet comes nearby. interior of the Earth is actually The backs of watches a magnet, with its own are always made from stainless steel to shield magnetic field flowing from the mechanism from the south pole to the north magnetic fields. pole

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Magnetic forces

Making and destroying magnets

geographic axis

S

N

7 Explain the term ‘domain’.

Earth’s magnetic north pole

true north pole

8 Describe how a material can be made magnetic. 9 Use a drawing to explain what the word ‘align’ means.

Magnetic fields 10 Draw magnetic fields for a bar magnet and a horseshoe magnet. 11 Identify where the magnetic field on a magnet is strongest and where it is weakest.

S

Magnetic Earth 12 Predict what the Earth’s core is made up of, given that the Earth has a magnetic field.

N

13 Explain how a compass works.

Think

Earth’s magnetic south pole

Bar magnets and the Earth have similar magnetic fields. The symbol at the top left shows the way a compass reacts in the Earth’s magnetic field.

Fig 7.6.5

Worksheet 7.5 Magnets

UNIT

7. 6

[ Questions ]

Checkpoint Introducing magnets 1 Suggest how magnets were given their name. 2 Identify whether magnetic forces are contact or non-contact forces. Explain your answer. 3 List the three metals that can be attracted to magnets.

Attraction and repulsion 4 Explain what a ‘pole’ is. 5 Identify the two poles found on magnets. 6 List the rules for attraction and repulsion of magnetic poles.

210

14 Copy the following and modify any incorrect statements so they become true. a The north pole of a magnet will attract other north poles. b Compasses are actually small magnets. c The area around a magnet is called its poles. d The ends of a magnet are called its magnetic field. e Domains must be aligned for a piece of iron to be a magnet. f The Earth does not have any magnetic field. 15 Magnets need to be stored carefully. Propose a set of recommendations for how they should be stored. 16 Steel ships often accidentally become magnetised while they are being built. Propose reasons for how this happens. 17 The Aurora Australis is an amazing show of lights in the night sky that only happens at the South Pole. It happens when particles from space follow the magnetic field of Earth until they enter the Earth’s atmosphere. a Draw the magnetic field of Earth, indicating where the field is strongest. b Indicate where the field lines actually touch Earth, and predict where on the Earth you would expect to see an aurora.

UNIT

7. 6 [ Extension] Investigate 1 Investigate what you think the word ‘ferromagnetic’ might mean. (Hint: Use the periodic table to find the chemical symbol for iron.) 2 Most permanent magnets are made from an alloy called Alnico. a Use a periodic table to identify the meanings of the chemical symbols Al, Ni and Co. b State the three elements that the alloy Alnico contains. c Propose a reason why each one might be included. 3 Research the uses of electromagnets in simple electrical devices such as doorbells and telephones. Produce a report to explain how these electromagnetic devices work.

5 The north pole is not exactly where a compass points! Explain the difference between the geographic and magnetic north poles. 6 Investigate how magnetism is used to record sound and images in cassette tapes, computer disks and videotapes. Draw a series of diagrams to show how these devices record information.

Surf 7 Find out more about compasses and make your own by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 7, and clicking on the destinations button.

4 Screwdrivers and screws are often accidentally magnetised when an electrical device such as a power drill has been operating nearby. Investigate how an electric motor works and how it could affect a screwdriver.

[ Practical activities ] Attracting and repelling

Prac 1 Unit 7.6

Aim To investigate the two poles of a bar magnet

Equipment Watch-glass, 2 bar magnets

S

N

N

UNIT

7. 6

Method 1 Balance a magnet on the back of a watch-glass. 2 Hold another magnet near the poles as shown and record your results in the table below. Magnets attract and repel.

North pole North pole South pole

South pole

Fig 7.6.6

Questions 1 Propose a rule for the attraction and repulsion of magnetic poles. 2 Explain the term ‘poles’.

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Magnetic forces

Prac 2 Unit 7.6

Getting magnetic

Magnetic fields

Aim To make an object magnetic

Aim To observe magnetic fields

Equipment A permanent magnet, a large nail, small pins or paperclips, polystyrene, cork or other floating material, bucket or ice-cream container

Method 1 Repeatedly stroke the large nail with the same end of the magnet, lifting it high at the end of each stroke. Count the number of strokes you make. 2 Keep stroking until the nail is able to attract some pins or paperclips.

Prac 3 Unit 7.6

Equipment A wooden board or bench mat, 1 sheet of waxed lunch-wrap, bar and horseshoe magnet, fine iron filings (preferably in a shaker), either access to a 200–300 W spotlight to be used as a heat source (CAUTION: the spotlight will be extremely hot)

Method 1 Place a magnet on the board or bench mat and lay a sheet of the waxed lunch-wrap over the magnet.

3 Now rest the nail on a float such as a piece of polystyrene.

2 Sprinkle a small amount of the iron filings onto the sheet, gently tapping the sheet to spread them out around the magnet.

4 Carefully rest the float on water in a bucket or ice-cream container.

3 Shine the spotlight onto the sheet to melt the filings into the wax.

5 Check the direction the nail points with that of a ‘standard’ compass.

4 You now have a permanent record of the magnetic field of the magnet—paste it into your workbook.

Fig 7.6.7

A compass is simply a magnet.

5 An alternative is to use hair spray to fix the iron filings to the paper. (CAUTION: check whether any students are allergic to perfumed hair sprays.)

Questions 1 Identify where the magnetic field was the strongest. 2 Identify and describe any positions on the magnet where no (or very few) filings were attracted. 3 Describe what you noticed about the strength of the field further away from the magnet.

Questions 1 State the number of strokes you made to magnetise the nail. 2 Describe whether the nail successfully acted as a compass. 3 Describe how you could check.

212

Chapter review [ Summary questions ] 1 Match the words with their correct meanings. Force

Caused by rough surfaces sliding

Spring balance

A unit of mass

Friction

Reduces friction

Newton

Forces that add up to zero

Lubricant

Push or pull

Heat

Causes large friction

Sandpaper

Produced by friction

Kilogram

A unit of force

Balanced forces

Measures mass

Balance

Measures weight

2 True or false? a Mass and weight are the same. b Gravity depends on the planet we are on. c The mass of an object depends on where we are in the universe. d There is no gravity on the Moon.

e The gravity on the Moon is less than on Earth. f Weight is measured in kilograms. g All objects have their own gravity and pull all other objects towards them. h A ship floats because its buoyancy balances its weight. i Buoyancy is a downward force. j Drag always makes objects go faster. 3 Classify the examples below according to whether friction can be seen as an advantage or a disadvantage. a stopping in a hurry b pushing a fridge across the floor c running a car engine d parachuting from a plane e turning quickly on your bike 4 Complete the following table to summarise how forces are important in our everyday lives. Give two examples for each type of force.

Type of force

Where used

How it works

Push

Skateboarding

Skateboarder pushes ground with foot to move forward

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Pull

Friction

Gravity

Magnetic

Buoyancy

213

>>> [ Thinking questions ] 5 ‘Reducing friction would make machines more efficient.’ Explain what is meant by this statement. 6 When we swallow food, there is a lot of friction from our throat. Explain what makes swallowing food easier. 7 Describe three ways in which a magnet can be made. 8 Explain how magnets can lose their magnetism. 9 Draw the magnetic field that exists around a bar magnet. 10 Explain what a compass is and how it can be made. 11 Identify three ways in which friction may be reduced. 12 Explain three situations in which it is important to be able to reduce friction.

14 Draw small, simple sketches of the following situations. On each, draw all the forces that are acting. a A kite is flown. b A basketball is thrown towards the goal. c A magnet affects a compass. d A fish is hauled in on a line. 15 Calculate the weight of a person on Earth who has a mass of 80 kg, if gravity is10 m/s2. 16 An astronaut has a mass of 91 kilograms on Earth. a Calculate their weight. The astronaut goes into space on a mission. b What would be their mass in space? c What would be their weight in space? Worksheet 7.6 Forces crossword Worksheet 7.7 Sci-words

[ Interpreting questions ] 13 For each of the diagrams below, identify whether it shows: • push • pull • friction • drag • buoyancy • surface tension • weight • magnetic force

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8

Earth and space Key focus area:

>>> The history of science

describe the spacing, size and movement of the planets explain how and why different astronomers developed different models to describe the solar system

Outcomes

list the planets of the solar system in order

4.1, 4.9.1

By the end of this chapter you should be able to:

compare conditions on each of the planets in the solar system. explain how the day, night, seasons and tides occur on Earth describe the motion of the Moon, and the conditions that occur there.

longer than its year?

2 Name the planets that humans have visited either in person or with probes.

3 Why do we experience longer days in summer than in winter?

4 How hot is it on the Sun? 5 The Moon has seas that are not really seas. What are they?

6 Name a famous astronomer.

Pre quiz

1 Which planet has a day that is

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UNIT

context

8. 1 For thousands of years ancient astronomers saw points of light that appeared to move among the stars. They called these ‘planets’, meaning ‘wanderers’, and named them after the Roman gods. If you look up at a clear night sky, you too will be able to see many of the planets that the ancient astronomers saw. You might

Theories of the solar system Pythagoras was a Greek scientist and mathematician who lived in the sixth century BC. Although he is best known for his important and useful rule for right-angled triangles (which you will study in Maths), Pythagoras also proposed a theory we now know to be wrong—he suggested that the Earth was the centre of the universe. Aristotle (384–322 BC), Hipparchus (died after 127 BC) and Ptolemy (127–145 AD) proposed more detailed models in which Earth was placed at the centre of the solar system. This type of model is known as the geocentric model (geo = Earth). The geocentric model by Ptolomy (left) and the heliocentric model of Copernicus (right)

Fig 8.1.1

Ce

ia l le s t

e containing all th spher es

also see an assortment of space junk and satellites that also move in the night sky. Today we use telescopes to have a close look at the planets and sometimes send probes to visit them. Because of this we have a much greater understanding than before of Earth and the eight other planets of the solar system in which we live.

Another ancient Greek, Aristarchus (310–230 BC) questioned the geocentric model and proposed instead a model in which the Earth and other planets revolved around the Sun. This is known as a heliocentric model (helio = Sun). Aristarchus also thought that the Moon went around the Earth. The geocentric model continued to be favoured until the end of the fifteenth century. Those who suggested otherwise were often in danger from the religious authorities, who thought that humankind and Earth had to be the centre of everything. In the 1530s, Polish astronomer Nicolas Copernicus (1473–1543) agreed with Aristarchus and suggested that the Earth and other planets orbited the Sun. There was fierce opposition to his ideas.

Saturn

t ar

Jupiter

s

Mars Moon Earth Venus

Mars

Mercury

Venus Moon Jupiter

Earth

Mercury Sun

Sun

Saturn Ptolemy model

216

Copernicus model

Galileo (1564–1642) was a strong supporter of Copernicus’s ideas, and in 1609 he used a telescope for the first time to make detailed observations of the Moon and planets. His observations exposed errors in the geocentric model. The Danish astronomer Tycho Brahe (1546–1601) did not support Copernicus’s heliocentric theory and took numerous detailed measurements of the positions of stars and planets in an attempt to Tycho Brahe’s nose improve the geocentric model. Body piercing may be Ironically, using Tycho Brahe’s thought of as a modern data, German astronomer Johannes fashion trend but in Kepler (1571–1630) finally the late 1500s Tycho Brahe’s gold and silver showed that Copernicus’s idea of a nose must have caused heliocentric model was correct. In 1566 his real a stir. nose was cut off in a sword duel with another student over who was the better mathematician.

The solar system

The term ‘solar system’ takes its name from the object at the centre of it all—the Sun, also known as Sol. The nine planets of the solar system, in order starting from closest to the Sun, are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. One way of remembering this list is to use a sentence like the following, which may sound a little crazy, but helps us remember the order (such a sentence is called a ‘mnemonic’): My Very Early Morning Jog Starts Up Near Phillip’s. The planets each orbit the Sun, rotating on their axes as they do so. The time taken for a planet to spin Fig 8.1.2

The planets to scale. The rings of the gas giants are not shown.

UNIT

8 .1 once on its axis is called its day, and the time taken to orbit the Sun once is called its year. All the planets have days and years of different lengths. The four innermost planets are called terrestrial (meaning ‘Earth-like’) and orbit the Sun in almost circular orbits. The other, outer planets move in elliptical or oval orbits. All planets move in the same plane (a large imaginary flat surface) except for Pluto, whose orbit is tilted by about 17° compared to the other planets’ orbits. For this reason, some astronomers think that Pluto should not be classified as a planet. The larger outer planets—Jupiter, Astronomical unit Saturn, Uranus and Neptune—are The average distance from known as the gas giants, because the Earth to the Sun is their outer layers are composed of called an astronomical unit, or AU for short, and equals gases such as hydrogen and helium. 149 600 000 kilometres. It was introduced by Copernicus and later defined by Cassini in 1672. To appreciate this distance, if you travelled at 100 kph it would take about 170 years to cover the distance.

The ancient planets

Following is a series of ‘fact files’ for the planets that were known by ancient civilisations and which we will call the ancient planets. All can be observed by the naked eye. The diameter measurements are made at the equator for each planet. For comparison, the diameter of the Sun is 1 392 000 km. The symbols used for each planet are still used by astrologers and were invented by the Greeks, who imagined each planet to be a god.

Mercury Mercury was known in ancient Sumer (now Iraq), some 5000 years ago. Since the planet moves very quickly across the sky, it was named after the Roman god, Mercury, who was the swift messenger of the gods. Symbol for Mercury

Fig 8.1.3

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The solar system

Fig 8.1.4

Mercury showing its heavily cratered surface

Mercury

Mercury’s missing rock Mercury is the second-smallest Scientists believe planet in the solar system and is Mercury has an iron the closest planet to the Sun but it core 75 per cent as large as the planet itself. interestingly, is not the hottest. Earth has a much lower Because it is so close to the Sun, it iron content. If both is often hard to observe, appearing planets were formed at as a morning or evening star. about the same time, Mercury should contain Mercury is in many ways similar more rock and less to Earth’s Moon, with a surface iron, so where did the containing craters, plains, and no missing rock go? Possible explanations atmosphere of its own. The are that the rock was Mariner 10 space probe flew past swept away by gas at Mercury three times in 1974 and the time Mercury was formed, or was 1975, photographing more than vaporised by a young half the planet’s surface. The Sun, or was blasted Messenger space probe was off by a collision with launched in 2004 and is the first an asteroid. spacecraft to have orbited the planet. Messenger will investigate Mercury’s geology, atmosphere and magnetic field.

Fact file

Venus

Mythology

God of travel, commerce and thieves

Mass

0.056 times that of Earth

Moons

None

Diameter

4878 km ( = 0.38 x Earth’s diameter)

Surface

Similar to Earth’s moon, with craters, lava-flooded plains and smooth mountains

Atmosphere

Mainly helium, which blows past Mercury from the Sun

Gravity

0.38 times that on Earth

Surface temperature

–170°C to 430°C

Period of rotation (day)

59 Earth days

Tilt of axis

0°

Distance from Sun

0.39 AU (58 million kilometres)

Symbol for Venus

Fig 8.1.5

Venus was recorded by the Babylonians in approximately 3000 BC and it is also mentioned in the astronomical records of the ancient civilisations of China, Central America, Egypt and Greece.

Time to orbit Sun (year) 88 Earth days

Scale model (Sun = 300 mm) Diameter

1 millimetre

Distance from Sun

12.5 metres Fig 8.1.6

218

Venus radar image from the 1990–94 Magellan mission

Venus Fact file

used radar imaging to map 99 per cent of the planet’s surface, which cannot be observed using telescopes because of Venus’s thick cloud layer.

UNIT

8 .1 Earth

Mythology

Goddess of love and beauty

Mass

0.815 times that of Earth

Moons

None

Diameter

12 103 km ( = 0.95 x Earth’s diameter)

Surface

Extensive cratering, volcanic activity. Mountain ranges, a 1500 km trench.

Atmosphere

80 km thick layer of carbon dioxide with some water vapour. Clouds contain concentrated sulfuric acid droplets.

Atmospheric pressure

90 times that on Earth (enough to crush early space probes)

Gravity

0.9 times that on Earth

Surface temperature

460°C

Period of rotation (day)

243 Earth days

Tilt of axis

30°

Distance from Sun

0.72 AU (108 million kilometres)

The third planet from the Sun,Earth is known as the blueor water planet and is the only planet currently known to support life. The Earth has a molten core topped by floating plates that make up its surface, 70 per cent of which is under water. The Earth is orbited by the Moon and many communication satellites. Symbol for Earth

Fig 8.1.7

Venus and Captain Cook Important early telescopic observations of Venus were conducted in the 1700s when Venus passed directly between the Sun and the Earth and was silhouetted against the Sun. This is called a solar transit. Captain James Cook observed the 1769 transit of the planet Venus across the Sun from Tahiti. He then sailed south to find the east coast of the southern continent, the so-called Terra Australi, (Australia) in 1770.

Earth showing Australia and Antarctica

Fig 8.1.8

Time to orbit Sun (year) 225 Earth days

Scale model (Sun = 300 mm) Diameter

2.6 millimetres

Distance from Sun

23.3 metres

Venus, the hottest planet, is a similar size to the Earth, but would be very inhospitable for humans, with its acidic and crushing atmosphere. Apart from the Sun and Moon, Venus (when visible) is the brightest object in the sky and is known as the morning and evening star. Venus is unusual for several reasons. It spins in the opposite direction to the Earth and other planets (that is, from east to west) and a Venus day is longer than its year. Mariner 10 flew past Venus on its way to Mercury in 1974. More recently, the Magellan Venus Orbiter

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The solar system

Earth Fact file Mythology

Gaia—mother Earth

Mass

1.0 times that of Earth (5 980 000 000 000 000 000 000 000 kg)

Moons

One (‘the Moon’)

Diameter

12 756 km

Surface

Two-thirds water, one-third land

Atmosphere

78% nitrogen, 21% oxygen, 1% carbon dioxide, argon and water vapour and other gases

Gravity

1.0 times that on Earth

Surface temperature

Average 22°C

Period of rotation (day)

1 day

Tilt of axis

23.5°

Distance from Sun

1 AU (150 million kilometres)

Time to orbit Sun (year)

365.25 days

across the sky gave ancient astronomers problems because it was sometimes direct and sometimes backwards (called retrograde motion). This was, however, explained by Kepler in 1609. The Viking 1 and Viking 2 space probes landed on Mars in 1976 after orbiting the Fig 8.1.10

Basic maths mistake destroys Mars probe The loss of the Mars Climate Orbiter has been blamed on a failure to convert units of thrust to metric units in software controlling the probe. Consequently the probe was positioned too close to Mars when it tried to enter orbit.

Mars showing red earth and polar caps

Scale model (Sun = 300 mm) Diameter

2.7 millimetres

Distance from Sun

32.2 metres

Mars Mars is the ‘red planet’ and has been the subject of numerous science fiction movies. Perhaps Mars should be called ‘the rusty planet’, as its red appearance is due to Symbol for Fig 8.1.9 rust (iron oxide) in its Mars surface soil and rocks. There are some similarities between Earth and Mars. A Martian day is only 30 minutes longer than an Earth day, and its 25° tilt causes seasons similar to Earth’s, only twice as long. The movement of Mars

220

The Sojourner rover sampling the large rock known as ‘Yogi’ on Mars in July 1997

Fig 8.1.11

planet and were used to look for signs of microscopic life. The results of these investigations are still being debated. In July 1997 the Pathfinder mission landed on Mars and placed a six-wheeled robotic rover, named Sojourner, on the surface to gather information about the rocks and weather. In September 1999, the Mars Climate Orbiter ‘disappeared’ while orbiting Mars. In 2003 two rovers, Spirit and Opportunity, were launched to search for evidence of liquid water at different regions on Mars. Further Mars space probe launches are planned in the future.

Mars Fact file Mythology

God of war

Mass

0.107 times that of Earth

Moons

2 (Phobos—diameter 23 km, Deimos—diameter 10 km)

Diameter

6794 km ( = 0.53 x Earth’s diameter)

Surface

Soft red soil containing iron oxide (rust), giving the planet its red appearance. Cratered regions, large volcanoes, a large canyon and possible dried-up water channels. Polar caps of frozen carbon dioxide and water.

Atmosphere

Very thin, mainly carbon dioxide

Gravity

0.376 times that on Earth

Surface temperature

–120°C to 25°C

Period of rotation (day)

1.03 Earth days

Tilt of axis

25.2°

Distance from Sun

1.52 AU (228 million kilometres)

Time to orbit Sun (year) 687 Earth days

Scale model (Sun = 300 mm) Diameter

1.4 millimetres

Distance from Sun

49.1 metres

The asteroid belt Orbiting the Sun between Mars and Jupiter is an asteroid belt composed mainly of small rocks and dust. The largest asteroid in the asteroid belt is Ceres, having a diameter of about 1000 kilometres. Another asteroid, Vesta, is visible from Earth with the naked eye.

Jupiter The largest of the planets, Jupiter has a diameter more than 11 times that of the Earth. Ancient astronomers named the planet Jupiter, for the ruler of the gods in the

Symbol for Jupiter

Jupiter showing alternating east and west wind belts. The Great Red Spot is the large oval shape.

Roman state. It is famous for its Great Red Spot, which is really a giant hurricane about three times the size of the Earth. In 1977, two space probes, Voyager 1 and Voyager 2, were launched. In March 1979, Voyager 1 flew by Jupiter and detected a

UNIT

8 .1

Fig 8.1.12

Fig 8.1.13

Shoemaker puts the boot in The Shoemaker-Levy 9 comet that struck Jupiter in 1994 was actually a series of 21 comets! The explosions caused by the impacts had the equivalent power of an atomic bomb going off every second for 5 or 6 years. Some of the resulting dust clouds were bigger than the Earth.

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The solar system faint series of rings around the planet measuring 29 km thick and 6400 km wide. The first active non-Earth volcano was also detected—on Io, one of Jupiter’s moons. In July 1994 the Hubble space telescope photographed the collision of the comet Shoemaker-Levy 9 with Jupiter.

Saturn He’s at it again! Remember Hooke from his discovery of cells? He was also one of the first men to build a Gregorian reflecting telescope and used it to discover a star in the constellation of Orion. Because of his telescope observations in 1664 he also suggested that Jupiter rotated on its axis. His detailed sketches of Mars were used in the nineteenth century to determine its rotation speed.

Jupiter

Saturn is the secondlargest planet in the solar system and is one of the most recognised due to its impressive ring system, which was discovered by Galileo in Symbol for Fig 8.1.14 1610. The rings are only Saturn tens of metres thick, but have a diameter of 270 000 kilometres. The rings are thought to be composed of particles of ice and icecovered rock, from tiny particles to large rocks. Like Jupiter, it is a world of gas, a planet so light it would float on water. The space probe Voyager 2 detected over 100 000 rings when it flew by Saturn in 1981.

Fact file Mythology

Ruler of the Gods

Mass

318 times that of Earth

Moons

At least 28 moons and four rings, including the four largest moons: Io, Ganymede, Europa and Callisto. These are known as the ‘Galilean’ moons.

Fact file

Diameter

Saturn Mythology

God of agriculture

Mass

95.184 times that of Earth

Moons

At least 30 moons and rings in seven bands

142 984 km ( = 11.21 x Earth’s diameter)

Diameter

120 536 km (= 9.45 x Earth’s diameter)

Surface

Liquid hydrogen

Surface

Atmosphere

Hydrogen (84%) and helium (15%). Upper layer contains white clouds, probably composed of solid ammonia.

Liquid hydrogen. Winds up to 1800 km/h

Atmosphere

Very thick layer of hydrogen and helium

Gravity

1.064 times that on Earth

Surface temperature

–180°C

Period of rotation (day)

10 hours 39 minutes

Tilt of axis

26.7°

Distance from Sun

9.6 AU (1400 million kilometres)

Gravity

2.525 times that on Earth

Surface temperature

Cloud top –150°C

Period of rotation (day)

9 hours 55 minutes

Tilt of axis

3.1°

Distance from Sun

5.2 AU (778 million kilometres)

Time to orbit Sun (year) 29.5 Earth years

Time to orbit Sun (year) 11.8 Earth years

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Scale model (Sun = 300 mm)

Scale model (Sun = 300 mm)

Diameter

30 millimetres

Diameter

25 millimetres

Distance from Sun

168 metres

Distance from Sun

307 metres

Uranus Fact file Mythology

Father of Saturn

Mass

14.54 times that of Earth

Moons

At least 21 moons and 11 rings

Diameter

51 200 km (= 4.01 x Earth’s diameter)

Surface

Likely to be frozen hydrogen and helium

Atmosphere

Hydrogen, helium and very turbulent, with winds over 600 km/h

Gravity

0.903 times that on Earth

Surface temp.

–220°C

UNIT

8 .1

Period of rotation (day) 17 hours 14 minutes

Saturn showing the cloudy atmosphere and the separation between the two bright rings (the Cassini Division)

Fig 8.1.15

Tilt of axis

98°

Distance from Sun

19.2 AU (2875 million klm)

Time to orbit Sun (year) 84 Earth years

Scale model (Sun = 300 mm)

The modern planets The following planets cannot be seen with the naked eye but need the assistance of a telescope and were discovered relatively recently. In fact, these planets do not appear in any textbooks printed before Captain Cook landed at Botany Bay in 1770. These books only show six planets—the ancient planets.

Diameter

10.1 millimetres

Distance from Sun

618 metres

Uranus Symbol for The English astronomer Uranus Fig 8.1.16 William Herschel accidentally discovered Uranus in 1781. Uranus’s axis is tilted at an angle of 98°, so it virtually lies on its side as it orbits the Sun. This tilt gives Uranus the strangest seasons of all the planets, with each season lasting 21 years. Like Saturn, Uranus has a large number of moons, and a ring system that is quite faint in comparison. Voyager 2 discovered additional moons and rings when it flew by in 1986.

Fig 8.1.17

Uranus showing the vertical rings and moons (white) orbiting the planet

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The solar system Neptune Sometimes referred to as the twin of Uranus, Neptune was identified by German astronomer Johann Galle on 23 September 1846 only after it was noticed that Uranus strayed from its orbit. The cause was the gravitational attraction of ‘nearby’ Neptune. The Great Dark Spot, which can be seen in Figure 8.1.19, is a huge cyclonic storm with winds up to 2400 km/h. Voyager 2 also flew past Neptune in 1989, examining the recently discovered rings that are the least known and understood of the rings Symbol for Fig 8.1.18 systems. Neptune

Neptune Fact file Mythology

God of the sea

Mass

17.15 times that of Earth

Moons

8 moons and 5 rings

Diameter

49 528 km ( = 3.88 x Earth’s diameter)

Surface

Frozen hydrogen and helium

Atmosphere

Mainly hydrogen, helium. Very high winds over 600 km/h

Gravity

1.135 times that on Earth

Surface temperature

–220°C

Period of rotation (day)

16 hours 7 minutes

Tilt of axis

29.3°

Distance from Sun

30.1 AU (4500 million kilometres)

Neptune showing its blue-green atmosphere. The Great Dark Spot seen at the centre is about 13 000 km by 6600 km in size.

Pluto Pluto is the outermost planet and was found by American scientist Clyde Tombaugh on 18 February 1930. It appeared as a dim ‘star’ that slowly changed its position against the fixed stars as it went on its 248-year orbit around the Sun. Since it was sighted it

Planet X

Symbol for Pluto

Fig 8.1.20

Time to orbit Sun (year) 165 Earth years

Scale model (Sun = 300 mm)

224

Diameter

9.7 millimetres

Distance from Sun

968 metres

Fig 8.1.19

has completed about a third of its orbit of the Sun. Pluto has an unusual orbit that actually comes inside Neptune’s orbit for 10 per cent of the time. Pluto is the smallest planet.

For several years, many scientists believed there was an undiscovered planet, ‘Planet X’, beyond Pluto that was responsible for unexplained deviations in the orbits of Uranus and Neptune. When Voyager 2 provided more accurate information about the masses of Uranus and Neptune, it was discovered that both planets were heavier than first thought. New calculations using these more accurate masses were then able to explain the deviations in orbit, ending support for the existence of Planet X.

There are plans for a probe to be launched in 2006 to arrive at Pluto in 2015. Recently there has been debate as to whether Pluto is a planet or a comet trapped by the Sun’s gravitational field.

Extrasolar planets As of July 2003, about 117 planets have been located revolving around other stars outside our solar system. Several of these are in what are called ‘habitable zones’ around their parent stars, where the temperature would permit water to remain in a liquid state. Perhaps life exists on one of these planets.

UNIT

8 .1 Pluto Fact file Mythology

God of the underworld

Mass

0.002 times that of Earth

Moons

1 (Charon)

Diameter

2300 km ( = 0.18 x Earth’s diameter)

Surface

Icy crust of methane

Atmosphere

Very thin, if any

Gravity

0.061 times that on Earth

Surface temperature

–223°C

Period of rotation (day)

6 Earth days

Tilt of axis

122°

Distance from Sun

39.6 AU (5914 million kilometres)

Time to orbit Sun (year) 249 Earth years Fig 8.1.21

UNIT

8 .1

Pluto is called a double planet because Charon (Pluto’s moon) is about half the diameter of Pluto.

Scale model (Sun = 300 mm) Diameter

0.4 millimetre

Distance from Sun

1275 metres

[ Questions ]

Checkpoint Theories of the solar system 1 Identify three astronomers who proposed that the Earth and other planets revolved around the Sun. 2 Explain what you think the underlined part of the following words means. a geocentric b heliocentric 3 Describe the difference between a geocentric and a heliocentric model of the solar system using a diagram. 4 Many scientists believed for long time that the planets revolved around the Sun, yet they did not speak up. Explain why you think this was.

The solar system 5 Identify the gas giants. 6 Unscramble these planet names. a PETENUN f ITUPREJ b SUNEV g SUNRAU c TOLUP h TEHAR d ARMS i RECYRUM e RATUNS

Worksheet 8.1 Saturn’s rings Worksheet 8.2 History of astronomy

Prac 1 p. 227

Prac 2 p. 227

7 List the planets in order from: a largest to smallest b closest to most distant from the Sun

The ancient planets 8 Clarify what is meant by a terrestrial planet. 9 Explain why the terrestrial planets are also classified as the ‘ancient’ planets.

The modern planets 10 This group of planets is not new. Explain why they are classified as the ‘modern’ planets. 11 Name two ‘modern planets’ and describe the main features that could be used to identify them.

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The solar system

k is two-thirds under water l has the most impressive ring system m was discovered because it was noticed that a neighbouring planet strayed from its orbit n has a day that is longer than its year o has the strongest gravity p is known as the morning and evening star q is the most dense

Think 12 Identify an object that is much smaller than a planet and which condensed from a cloud of interstellar gas and dust. 13 Identify three space probes, and at least one planet visited by each. 14 Identify the space probes that disappeared in 1999. 15 There is less information available about the outer planets than the inner ones. Explain why.

20 Identify which planets have: a moons b ring systems c methane in their atmosphere

16 Propose a reason why it is unlikely that life exists or has existed on planets other than Earth. 17 Estimate the diameter of Pluto’s moon, Charon, and its distance from the planet using Figure 8.1.21. (Hint: the diameter of Pluto is 2300 km.)

Skills 18 Construct a table to summarise the main astronomers in this unit. Include three columns for their name, date and a description of their ideas and discoveries. 19 Identify which planet: a is the hottest b is the coldest c has a giant hurricane raging that is larger than the Earth d doesn’t have its own atmosphere e spins the opposite way to all the others f has a similar day length to the Earth’s g spins on its side as it orbits the Sun h has a crushing atmosphere i has a rusty surface j is covered by a thick yellow layer composed mainly of carbon dioxide

21 Choose any three planets. Construct a table like the one below and enter the data for each planet. Planet name

__________

__________

__________

Mass Diameter Surface Atmosphere Gravity Surface temperature Moons Period of rotation Distance from Sun Time to orbit Sun

Create 22 Construct a three-dimensional model of the solar system using common spherical objects.

[ Extension] Investigate 1 a Calculate planet sizes or distances from the Sun for a scale diagram of the solar system that will fit on poster paper. b Construct your scale model on paper. (Hint: you may need to change one of the scales to make it fit.) c Explain why it is not convenient to have both size and distance to scale.

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2 a Investigate what or who each planet was named after. b Construct a booklet that summarises this information, including pictures of each planet and the person or object the planet was named after.

Action 3 ‘Money spent on space exploration would be better spent on things like medical research and aid programs.’ Research what this statement means and have a class debate on this issue.

Surf Find out more about the solar system by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8 and clicking on the destinations button. 4 Construct a model of a space probe such as the Cassini spacecraft that is currently on its way to explore Saturn. 5 Investigate the planets further through pictures, games and information on the Internet.

UNIT

8 .1

Creative writing Postcard from another planet The year is 3000 and you are on holidays at a resort on another planet in the solar system. Construct a postcard, complete with stamp, and write a letter describing your holiday to someone back home on Earth.

[ Practical activities ] Classification of the planets

A model solar system Prac 1 Unit 8.1

UNIT

8 .1

Aim To represent the relative sizes and distances of the planets Equipment Modelling clay, model information from Unit 8.1, a basketball to represent the Sun, photocopy of street map of the local school area, trundle wheel

Method 1 Split into small groups of students. 2 Copy the ‘scale model’ information from the ‘fact file’ for each planet into one table. 3 Using clay or play dough, make a model of each planet according to the size in the scale model. 4 Obtain a street map of the local school area. Decide where the Sun will be located and use the scale of the map to find the position of the outer five planets. 5 Go outside and place the Sun in position. 6 The inner planets should be placed in position from the Sun within the school grounds. Measure the distance for each planet using a trundle wheel. 7 Ask your teacher whether your group may place the outer planet models in position outside the school grounds. Measure the distance for each planet using a trundle wheel and check your street map to see if this is correct. Otherwise, mark on the street map where the other planets should be located.

Prac 2 Unit 8.1

Aim To classify the planets using different criteria

Method 1 The classification used in Unit 8.1 was according to history—ancient and modern planets. 2 Reclassify the planets according to the following rules. a Size—small planets have diameters less than 13 000 km, and large planets greater than 13 000 km. b Composition—rocky or terrestrial planets, and gas planets. c Distance from the Sun—the inner planets and the outer planets. The asteroid belt is the separating boundary. 3 Write a key for identifying the planets from their descriptions. 4 Use someone else’s key to identify the planets and evaluate whether their key is effective.

Questions 1 Describe any problems that you had when classifying Pluto.

Questions 1 For the outer planets, did the distance measured by the trundle wheel agree with the position marked on your street map? 2 Compare the spacing of the inner planets to that of the outer planets.

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Science focus: Early astronomy Prescribed focus area: The history of science For people who live in a city, when they look into the sky on a clear night, they do not see many stars. When you are in a location where it is truly dark, a clear view of the stars and planets can be an aweinspiring experience. Considering this, it is easy to understand why ancient humans were fascinated by the stars and planets.

Fig SF8.1

With no light pollution, a view of the Milky Way is amazing.

Nearly all early cultures had their own ideas on the stars and planets. Most studied the way they moved across the night sky, and many were worshipped as gods. Others used observations of their motion to make predictions about events such as the seasons. The available evidence suggests that astronomy (the study of the motion of the stars and planets) began around 3000 BC when the Mesopotamians, Egyptians and Chinese grouped stars together into constellations (collections of stars). Large structures like the pyramids and Stonehenge, constructed about 2500 BC, show how important the motion of the Sun and other objects in the night sky was to these ancient humans.

228

Astronomy and indigenous Australians The Australian Aboriginals were keen observers of the movement of the Sun, Moon and stars. Like the Inca people in South America, some indigenous tribes saw the Milky Way as a pathway to the ancestors and the dreaming spirits. The Aboriginal tribes used the motion of the stars across the night sky to predict the seasons and the time when certain food sources would become available. The constellations of the Southern Cross (Crux) and the seven sisters (Pleiades) are known to be of special significance to the Aboriginals, although each tribe often had different names and dreaming for them.

The seven sisters, known as Pleiades, as seen by the Aboriginals

Fig SF8.2

For the Pitjantjatjara tribe, originally inhabiting the Western Desert area, the Pleiades' first appeared in the east, just before dawn, was a signal that the dingoes would be having pups. The people would then know that, if they searched the dingo lairs, they would find newly born pups. For the Aboriginal tribes in the south-east of Australia, their dreaming story for the Pleiades (now commonly called the Seven Sisters), had the stars as seven young women. They believed that the young women had shown a lot of courage and insisted on doing all the tribal initiation rites that the men had to do. In honour of their bravery they were placed into the heavens together after their life on Earth, to act as a role model for others.

An early model of the solar system Claudius Ptolemy developed the geocentric model of the solar system (see Unit 8.1) using star measurements taken by the Greek, Hipparchus. Ptolemy wrote a famous book called the Almagest, which was produced in Babylon in about 150 AD. This book provided the first reasonably accurate way to predict how various objects moved across the sky. Those who used the information in the Almagest were able to predict, within about a hand span, where a star or planet would be in the night sky at any date and time. Ptolemy’s model was based on Aristotle’s idea that the objects of the heavens were ‘all perfect’, and moved in perfect circular orbits around the Earth. Because this is not totally correct, Ptolemy made some clever changes to enable his model to predict the motions more accurately.

The Ptolemy model predicted that Antares, a red star in the constellation of Scorpio, should be in the position where the thumb tip is. Ptolemy’s model was accurate enough to predict that Antares would be found somewhere within the circle, formed when the hand is rotated around the thumb.

Fig SF8.3

The influence of culture and religion During the fifteenth century the growing Christian church adopted the geocentric model as religious truth, and believed it to be in line with biblical teachings. But having the Earth at the centre of God’s created universe was to prove a very difficult issue.

Fig SF8.4

Ptolemy with Urania, the Goddess of astronomy. Ptolemy is holding a quadrant used for measuring the altitude of stars. In the bottom left corner is an astrolabe for measuring the altitude and position of stars and planets.

The Polish astronomer Nicolaus Copernicus began to examine all the available astronomical data and Ptolemy's model. Copernicus thought that Ptolemy’s model needed too many modifications to make it accurate. He suggested that this model could not truly reflect a perfect design from God. Copernicus produced a short paper in 1514, where he proposed his solution: a heliocentric model with the Sun at the centre. But Copernicus’s ideas were frowned upon and viewed by some in the Church as heresy. Copernicus continued to work on his heliocentric theory, completing a book in 1530. Because the Church disapproved of his ideas, his book was not published until 1543. Copernicus only saw a printed copy of the book on the day he died. The book was eventually banned in 1616 and placed on the Church's official ‘Index of forbidden books’, where it remained until 1835.

229

Pages from the book published by Copernicus in 1543 that described the heliocentric model of the solar system

Fig SF8.5 1

2

Fig SF8.7

Slow to change Despite the banning of Copernicus’s book, copies had become available. When the Italian, Galilei Galileo, read the book, he found that it made good sense and became a strong supporter of the heliocentric model. Galileo made a telescope and used it to examine the Moon and Jupiter. He showed others the mountains and craters of the Moon, and the moons orbiting around Jupiter, both of which were contradictory to what the Church believed. Galileo was condemned by the Church and forced to publicly declare that he was wrong to believe in a heliocentric model, and that he had misled others with the images they had seen through his telescope. He was kept under house arrest for the rest of his life. Galileo was finally given a reprieve by the Church in 1993. Better late than never!

Jupiter and the two Galilean moons, named after Galileo, who first viewed them through a home-made telescope

[ Student activities ] 1 We only know a few of the ideas and stories that Aboriginal people had regarding the stars and planets. a Think of and record reasons why this is the case. b Discuss your ideas with classmates. c Research to find more information about Aboriginals and astronomy by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8, and clicking on the destinations button. 2 The Milky Way is spectacular from a very dark location. a Research the Milky Way. Explain what it is and why it lights up the night sky so brightly. b Find a story that involves the Milky Way and retell it by writing a picture story book. 3 In his effort to get his idea across without causing more trouble with the Church, Galileo d use a poem to describe his ideas about the motion of the planets and stars. This got him getting into even more trouble. Imagine you are Galileo and first see the Moon with a telescope. Using the image of the Moon, write a short poem to try to describe it. 4 a Describe three reasons why most early people, and the church officials, could not believe that the Earth was in orbit around the Sun. b Design and perform an experiment or measurement to prove that the Earth is moving around the Sun and not the Sun around the Earth.

Fig SF8.6

230

Galileo demonstrating his telescope in 1609

5 One of the brightest stars in the night sky is AlphaCentauri. This star is found in the Pointer to the Southern Cross. Use the Internet to investigate and record any interesting information on Alpha-Centauri and give reasons why it might be considered ‘special’.

UNIT

context

8. 2 Historically many cultures have recognised the Sun as a god, demon or spirit. Whatever role the Sun takes, most cultures see it as the prime controller of all life on Earth. It is true that we depend on the Sun to supply the energy that has allowed life to flourish on Earth.

The importance of the Sun The Sun, also known in astronomy as Sol, is our nearest star and is currently in ‘middle age’, being about 4.5 billion years old, with another 4.5 billion years of ‘life’ left. Astronomers believe that the Sun is a second-generation star formed after a previous star collapsed, its debris combining with interstellar gas to form the Sun. The Sun is our source of heat and light energy and so is crucial to the continuation of life on Earth. Plants use energy from the Sun to help them make the food they need for growth, and in the process make oxygen. Animals that feed on plants, and the animals that feed on those animals, also depend on the Sun. Astronomical unit Deposits of dead plants and The distance from the animals in the Earth’s crust have Earth to the Sun is been converted over millions of called an astronomical years into oil, coal and gas and unit, or AU for short, and equals are further examples of energy 149 600 000 kilometres. sources related to the Sun. Solar An astronomical unit

Fig 8.2.1

The Sun showing a spectacular solar flare about 588 000 km across the solar surface

cells can now convert the Sun’s energy into other forms of energy and are being used more and more widely as technology improves their efficiency. As well as heat and light, other types of radiation such as ultraviolet (or UV) radiation reach us from the Sun. The Earth’s atmosphere screens out much of this harmful radiation, and provides an insulating layer to trap heat. Different parts of the Earth heat up by different amounts, creating pressure differences in Free-floating planets the atmosphere, which in turn Astronomers have create winds that increase recently discovered evaporation, leading to rainfall. several planets that do The Sun also provides the not appear to be orbiting stars but just drift massive gravitational force through space. necessary to keep the Earth and other planets in orbit around it.

Energy production in the Sun

1 AU

Earth Sun

Fig 8.2.2

Like all stars, the Sun produces energy in reactions in its core. The temperature and pressure at the core cause hydrogen particles to fuse or join together and form helium. This reaction releases a huge amount of energy and is called nuclear fusion.

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The Sun A million Earths The term ‘nuclear’ is used because each particle referred to above is really the centre, or nucleus, of a hydrogen atom. You will study more about atoms later in Science.

It would take 1.3 million Earths to fill the inside of the Sun, and 109 Earths would fit in a line across the Sun’s diameter.

Solar statistics The term solar is used to describe things associated with the Sun. The Sun is a star, but because it is much closer than other stars, it appears much larger and brighter.

Sun Fact file Mythology

The Sun God. Greeks called it Helios

Mass

333 400 times the mass of the Earth

Diameter

1 392 000 km ( = 109 x Earth’s diameter)

Gravity

28 times that on Earth

Surface temperature

6000°C (average). From 4500 to 2 000 000°C up to 15 000 000°C in the core.

Period of rotation (day) Equator 26 days, poles 37 days Tilt of axis

122°

Scale model Diameter

300 millimetres

Features of the Sun Several features of the Sun may be Rotation rates Different parts of the Sun observed from the Earth using rotate at different rates. special solar telescopes. The solar equator rotates CAUTION: Although we can once every 26 days, see these features from Earth, you while the Sun’s polar regions rotate once should never look at the Sun every 37 days. unless you are using special protective apparatus, as you can permanently damage your eyes. In 1611 Galileo observed for the first time sunspots and solar flares on the Sun’s surface. Sunspots are depressions on the Sun’s surface that appear darker because they are several thousand degrees cooler than the surrounding gas. The number of observable sunspots follows an 11-year cycle, and varies from zero to about 200 in a year. Solar flares come from sunspots and can reach a height of hundreds of thousands of kilometres above the Sun’s surface. These Prac 1 can cause interference with radios and p. 234 television on Earth. Prominences are a larger type of solar eruption and consist of a streamer of glowing gas. They can be observed from Earth during a total solar eclipse. Solar flare The Sun’s atmosphere radiation Due to a solar flare, consists of three main layers passengers in an aircraft as shown in Figure 8.2.4. The may receive radiation layers are: the visible surface of equivalent to that of one the Sun or photosphere; a thin medical X-ray. ring around the edge of the Sun, called the chromosphere; and a

corona (1 000 000°C–2 000 000°C)

Earth

chromosphere (4500°C–1 000 000°C) photosphere (5000°C) Sun

The Earth and Sun compared

232

Sun

Fig 8.2.3

The Sun’s atmosphere has three main layers.

Fig 8.2.4

faint halo extending out a great distance, known as the corona. The corona includes clouds of gas called prominences. The Sun is constantly emitting a stream of particles into space at speeds of about 500 kilometres per second. These solar winds send particles towards the Earth’s north and south polar regions, where they interact with gas particles in the atmosphere to cause Fig 8.2.5

Aurora Australis—the Southern Lights

spectacular light displays called aurorae. One such display occurs in Antarctica and is called the Southern Lights or Aurora Australis.

UNIT

8 .2 Solar eclipses The word ‘eclipse’ comes from the Greek word for ‘abandonment’—the eclipse was seen as the Sun abandoning the Earth. There are three types of solar eclipses. • A total solar eclipse is when the Sun is covered by the Moon. • A partial solar eclipse is when the Moon covers only part of the Sun. • An annular solar eclipse occurs when the Moon is at its greatest distance from the Earth. All solar eclipses occur when the Moon comes between the Earth and the Sun and the Moon’s shadow falls on the Earth, as shown in Figure 8.2.7.

total solar eclipse

Sun is behind Moon

Fig 8.2.6

How an aurora occurs

Moon

partial solar eclipse

solar corona now visible

annular solar eclipse

Moon Sun Moon Sun

solar wind aurora

Fig 8.2.7

There are three types of solar eclipse. Solar eclipses can occur up to twice a year but do not all happen in the same place.

Worksheet 8.3 Sunrise, sunset

night atmosphere aurora

8.2 UNIT

day

[ Questions ]

Checkpoint The importance of the Sun 1 Identify two types of energy provided by the Sun. 2 Plants and animals both depend on the Sun for food. Explain how.

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The Sun

3 If there had been no Sun, explain why there would also be no oil deposits inside the Earth.

13 The Sun is less dense than the Earth. Explain how this can be when the Sun is much bigger and has a much larger mass.

4 Name a harmful type of radiation from the Sun.

Energy production in the Sun.

14 List the following in order from closest to most distant from the centre of the Sun: chromosphere, photosphere, corona.

5 Explain what each word means in the term ‘nuclear fusion’.

15 a Identify the region of the Sun’s outer atmosphere that is the hottest. b State the maximum temperature that may be reached there.

6 State whether nuclear fusion is a chemical reaction or a nuclear reaction.

Features of the Sun 7 Identify three features of the Sun. 8 Describe each feature you have listed.

Solar eclipses

[ Extension]

9 Draw a diagram to demonstrate the view from Earth during: a a partial solar eclipse b an annular solar eclipse

Investigate 1 Investigate where an aurora other than Aurora Australis occurs, and what it is called.

Think 10 Explain how the Sun affects: a rainfall b wind

2 Investigate what the Ulysses probe is and construct a labelled diagram of its structure to show what it can do.

11 Identify the name of our nearest star and its distance from Earth.

3 a Research when the next eclipse will occur that can be seen from your local area. b Produce an advertisement to get people out to watch the eclipse. Remember to inform them how they can safely view the event without damaging their eyes.

12 If the Earth is drawn as a circle of diameter 1 mm, identify how large the Sun would be on the same diagram if the diagram is to be drawn to scale.

UNIT

8.2

[ Practical activity ] The sunspot cycle Equipment

Prac 1 Unit 8.2

2 If the graph follows a similar cycle for the next 11 years, sketch the predicted number of sunspots up to 2009.

Graph paper

3 How many sunspots do you predict for this year? If possible, check your prediction using the Internet.

Method 1 The approximate numbers of sunspots recorded over a 14-year period are given below. Use these data to construct a sunspot line graph. Place the years on the years on the horizontal axis.

Year Sunspots

234

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001 2002

157

142

146

94

54

30

18

9

22

64

93

120

111 104

UNIT

context

8. 3 The ancient civilisations defined the days, seasons, months and years by following the movements of the Sun and Moon. Babylonians, Mayans, indigenous Australians and many other cultures all developed complex ways to predict seasonal changes. This enabled people to plan when to plant crops or move to a new location in search of seasonal foods. Survival depended on this ancient scientific knowledge of the Earth’s movement in space.

Day and night are not usually of equal length, except at the equator. This is caused by the tilt of the Earth’s axis. The diagram below shows the Earth in a position where the southern hemisphere experiences longer nights than days.

Day and night

Sunrise and sunset The names ‘sunrise’ and ‘sunset’ seem to imply that it is the Sun’s movement that causes them. In fact it is the Earth spinning towards the Sun that causes sunrise. Sunset is caused by the Earth spinning away from the Sun.

area about to experience sunset

The Earth spins on its axis (an imaginary line joining the north and south poles) once every 24 hours. It is because of the Earth’s spin that we experience day and night. The part of the Earth receiving light directly from the Sun is experiencing day, while the other side, not receiving direct sunlight, experiences night. The direction of this spin is from west to east. This is why people in the east of Australia (e.g. Sydney) start each day before those in the west (e.g. Perth). The Earth spins on its axis, causing alternating day and night.

Sun Earth

area about to experience sunrise

Fig 8.3.2 Fig 8.3.1

Point A is about to experience ‘sunrise’, while on the other side of the Earth point B is about to experience ‘sunset’.

N

N

light from the Sun

equator equal length day and night longer nights

light from the Sun

longer days

northern hemisphere

S

southern hemisphere

S night

23.5°

day

When Earth is in the position shown, days are shorter in the southern hemisphere and longer in the northern hemisphere.

Fig 8.3.3

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Earth’s movement in space The year The time taken by a planet to orbit (travel around) the Sun is called a year. Earth spins on its axis while it orbits the Sun, just as a spinning top may move in a circular path while it spins. The Earth spins once on its axis in a day, and takes a year to orbit the Sun.

Fig 8.3.4

1 year

It is the Earth’s orbiting of the Sun that causes stars to appear in different positions throughout a year and the length of day and night to change through the year.

Seasons As the Earth orbits the Sun, the tilt causes different parts of the Earth to experience different heating effects—in other words, different seasons. In summer, the Sun’s energy is concentrated over a smaller area, and therefore produces a greater heating effect and higher temperatures. In winter, the same amount of energy is spread over a larger area and that area does not heat up as much.

Sun

Seasons in the southern hemisphere

Fig 8.3.6

1 day southern autumn equinox 21 March

N

Earth

An Earth year is not quite 3651/4 days. So that our calendar has an exact number of days, it is based on 365 days, with an extra day added in February each leap year. Generally, a leap year occurs every four years and is divisible by 4, but years ending in 00 (1900, 2100, 2200, etc.) are not leap years unless they are divisible by 400. Fig 8.3.5

southern winter solstice 21 June

Sun

southern summer solstice 21 December

southern spring equinox 21 September

Different concentrations of light and heat from the Sun produce the seasons.

same amount of heat/light from Sun heat/light from Sun line of latitude winter (heat/light spread out)

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spread over large area

spread over smaller area same latitude

summer (heat/light concentrated)

The Earth may be thought of in terms of two hemispheres, or half spheres. When it is summer in the southern hemisphere (which contains Australia), it is winter in the northern hemisphere. At the summer solstice, days are longest, and at the winter solstice, days are shortest. Between these two times, at the two equinoxes, day and night are of Prac 1 equal length. p. 238

UNIT

8.3

[ Questions ]

11 If the Earth’s axis was not tilted, explain whether there would be: a seasons b day and night

UNIT

8 .3 12 If the Earth tilted even more, explain how the seasons would be affected. 13 Describe the difference between an equinox and a solstice. 14 It is hot at the equator all year. Explain why.

Analyse 15 Identify which is longer, day or night, for the area marked A on Earth in Figure 8.3.7.

Checkpoint Day and night 1 Clarify what is meant by the ‘Earth’s axis’. A

2 State how long it takes the Earth to rotate once on its axis.

The year 3 State how long it takes the Earth to travel once around the Sun. 4 True or false: a A leap year is one that 4 divides into without any remainder. b The year 2000 was a leap year. c The year 2100 will be a leap year.

Seasons 5 Describe the feature of the Earth that is responsible for the seasons. 6 State the angle of the Earth’s tilt. 7 Clarify the following terms: a hemisphere b line of latitude c solstice d equinox

Sun

Earth

Fig 8.3.7 16 Identify which direction the stars appear to move: west to east, or east to west. Hint: Think about the direction of the Earth’s rotation. 17 Use Figure 8.3.6 to determine when the particular seasons occur in the northern hemisphere compared to the southern hemisphere.

8 Draw a diagram to demonstrate your understanding of how a season occurs.

Think 9 Identify the location on Earth where day and night are always the same length. 10 a Identify the location on Earth where it could be dark for more than 24 hours at a time. b Explain why this is possible.

237

Earth’s movement in space

>>>

[ Extension] Investigate 1 Use newspapers or other sources to record sunrise and sunset times for two weeks. Describe any changes in the length of day and night. 2 Investigate and explain aphelion and perihelion. 3 Research what the five climatic zones on Earth are and produce a poster to display your information, with examples of what these zones commonly are like. 4 Investigate at what speed the Earth: a spins on its axis b moves around the Sun

Creative writing Not in a spin! Scientists have just announced that the Earth is about to stop spinning on its axis! What may be the consequences? How will the weather and climate be affected? Will plants grow? Is this the end, or will life be possible in some areas? Write an account of how you prepare, and events afterwards.

Create 5 a Construct a model to demonstrate either the seasons, day and night, or the year. b Present your model to the class to teach them about your chosen concept.

UNIT

8.3

[ Practical activity ] Fig 8.3.8

A model Earth Aim To model night, day and the seasons Prac 1 Unit 8.3

Equipment

sphere (Earth)

mark where you live (approximately!)

A sphere (e.g. a ping pong ball or foam ball), a skewer or fine rod, a wedge, a lamp, a piece of string (60 cm)

Method

rod

1 Assemble the apparatus as shown in Figure 8.3.8, and place a mark on the Earth model to represent where you live. 2 Rotate the Earth model on its axis to simulate day and night.

string lamp (Sun)

wedge

3 Keeping the axis at the same angle, move the model around the lamp (the Sun) while a partner keeps it spinning on its axis to simulate day and night. 4 Repeat step 3 as required in order to complete the questions.

Questions 1 Explain the purpose of the piece of string. 2 Describe what you notice about the length of day and night as you move around the ‘Sun’. 3 Draw and clearly label a diagram to demonstrate your model in four positions representing each season.

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UNIT

context

8. 4 The Moon has inspired more stories, myths, prayers and rituals than anything else in history. Look at a full moon and you will see why different cultures see a man, a rabbit or a woman weaving. The name of the goddess Luna was given to the belief that a full moon makes people mad—lunatics.

Introducing the Moon Apart from the Sun, the Moon is the most obvious light in the sky. We see it shine because it reflects the light from the Sun. The Moon is much smaller than the Earth, having a diameter about the distance from Sydney to Perth. The Moon is the only celestial body on which humans have landed, beginning with the Apollo 11 mission in 1969, when Neil Armstrong uttered those now famous words: ‘One small step for man, one giant leap for mankind’. Buzz Aldrin near Apollo 11 and the US flag. Buzz was the second man on the Moon.

Easter is also associated with the Moon, as it falls on the first Sunday after the first full moon after 21 March. Maybe the Easter bunny is related to the image some cultures see in the Moon.

Astronauts must wear space suits with breathing apparatus on the Moon, as the Moon has no atmosphere and therefore no air to provide oxygen to breathe. Though astronauts have the same mass on the Moon as they do on Earth, their weight (the force of gravity on them) is about one-sixth on the Moon because the Moon is much smaller than the Earth. So lunar astronauts were able to take huge leaps and jump further than on Earth before falling to the surface once more.

The Moon Fact file

Fig 8.4.1

Mythology

God of the night

Mass

0.012 times that of Earth

Diameter

3476 km ( = 0.27 x Earth’s diameter)

Gravity

0.16 times that on Earth

Surface temperature

–230°C to 123°C

Period of rotation (day)

27.3 days

Time to orbit Earth

29.5 days

Tilt of axis

5°

Notice that the time for the Moon to orbit the Earth is nearly the same as the time it takes to spin once on its axis—this results in us only ever seeing the one side of the Moon from Earth. The other side is often called ‘the dark side of the Moon’ since it had never been seen until the Apollo missions.

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The Moon The lunar landscape

Phases of the Moon

In 1609, Galileo first used a telescope to view details of the Moon’s surface, which many had previously thought to be smooth. The two main types of lunar landscape he observed were plains (called maria) and highlands (which includes craters). An Italian Jesuit astronomer, Giovanni Riccioli, in 1651, thought the dark areas on the Moon were seas. This method of naming continues today, even though the Moon has no surface water, with names such as ‘Sea of Tranquility’ and ‘Sea of Serenity’. Though only one face of the Moon is visible from Earth, space probes have photographed the other side (‘the dark side’) to reveal very few maria there.

The Moon takes about a month to orbit the Earth, and spins at a similar rate, and therefore we always see the same face of the Moon. How much of the Moon’s face we see depends on where it is in its orbit around the Earth. We call these different views phases. There are eight Once in a main phases of the Moon. blue moon To understand Figure 8.4.3, We have all heard the imagine yourself on the Earth, saying ‘once in a blue under point A looking towards moon’, which means ‘not very likely’. But what Moon A. Because the Sun is is a blue moon? It is directly behind the Moon, the name given to the you see nothing of the Moon second full moon in the same month. Since the (we call this a new moon). time between two full Now imagine yourself on moons is 29.5 days Earth under point C, looking and a month is about 30.5 days, a blue moon directly towards Moon C. is rare, occurring only From here you would see once every two and only half the Moon. a half years.

C sunlight D

C B

D E

A full moon showing dark areas of lava-filled impact basins

Fig 8.4.2

Scientists believe that about 4 billion years ago the Moon was a hot, fluid mass that eventually cooled enough to form a crust. This crust was bombarded by meteorites to create the highland regions. Some of the depressions caused by meteorite impacts were filled with lava from lunar volcanoes that solidified to form large, Prac 1 p. 244 smooth areas or maria. In 1971 and 1972, Apollo missions discovered that the interior of the Moon is still hot. In 1998, the Lunar Prospector found evidence of water in the form of ice mixed with lunar dirt at the Moon’s poles.

240

B

A

E

full moon (fully visible)

F

new moon (nothing visible)

H G

F

A

H

G sunlight

Fig 8.4.3

Look from a letter on Earth to the same letter near the Moon and try to imagine the view from Earth in each case.

Now try the other positions (D to H) and check out how each phase occurs. A summary of the phases is shown in Figure 8.4.4.

Prac 2 p. 244

new moon

A

waxing crescent

first quarter

gibbous

B

C

D

full moon

E

gibbous

third quarter

waning crescent

F

G

H

UNIT

8. 4

?

views of the Moon from point on Earth

Fig 8.4.4

The eight phases of the Moon Why tides occur

Fig 8.4.6

low tide

water pulled by Moon’s gravity

Earth N

Moon high tide water not as strongly attracted by Moon’s gravity is ‘left behind’, causing another high tide

A composite image of the phases of the Moon

Fig 8.4.5

Tides As early as the second century BC, the Chinese had recognised a connection between tides and the Moon’s cycle. About twice a day the sea level rises to a high tide and falls to a low tide—the average time between two high tides is 12 hours 25 minutes. It was not until Newton proposed a theory of gravity in 1687 that tides were understood to be the result of the Moon’s gravitational pull on the Earth.

The gravitational force between two objects is only noticeable when one or both objects are very large, as is the case with the Moon and the Earth. The Moon attracts the oceans towards it, enough to cause a bulge in the oceans facing the Moon. If this were the only effect there would only be one high tide and one low tide a day, not two. The Earth’s rotation, however, causes a similar bulge on the other side of the Earth.

Lunar eclipse A lunar eclipse occurs when the Moon passes into the shadow of the Earth, as shown in Figure 8.4.7.

A lunar eclipse

Fig 8.4.7

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The Moon Lunar eclipses occur in stages as shown in Figure 8.4.8. Lunar eclipses can occur up to three times a year.

UNIT

8. 4

Fig 8.4.8

Stages of a lunar eclipse

view from space G penumbra

[ Questions ]

F E Sun

Checkpoint

Earth

D C

Introducing the Moon

B

1 Clarify what is meant by ‘celestial’.

4 State whether the Moon has: a atmosphere b gravity

penumbra

A

2 State the year when the first person walked on the Moon, and identify who it was. 3 Identify who the second person was to walk on the Moon.

umbra

Moon’s orbit

view of Moon from Earth penumbral eclipse

partial eclipse

total eclipse

B

C

D

5 State how far the Moon is from the Earth, rounded to the nearest 1000 kilometres. 6 Identify who used a telescope to view the Moon in 1609.

A

E

F

G

The lunar landscape 7 Identify the two main types of lunar landscape, and briefly describe them. 8 Identify where water may exist on the Moon. 9 Describe what the Apollo missions discovered about the core of the Moon.

Phases of the Moon 10 State how long it takes for the Moon to orbit the Earth. 11 Explain why we always see the same side of the Moon. 12 Explain what a ‘phase’ of the Moon means. 13 Draw each of the following: a a gibbous moon b a crescent moon

Tides 14 Identify what causes the tides on Earth. 15 State the number of tides that occur per day. 16 Draw a diagram to demonstrate how the tides are created.

Lunar eclipse 17 Describe how a lunar eclipse occurs.

Think 18 More meteorites reach the surface of the Moon than the surface of the Earth. Propose a reason why. 19 Identify the number of Moons (approximately) it would take to equal the mass of the Earth. A 10 B 100 C 1000 D 10 000 E 1 000 000 20 Explain the difference between a waxing crescent and a waning crescent. 21 Predict how the tides would be affected if the Moon was: a larger b further from the Earth 22 Explain what happens during: a a penumbral lunar eclipse b a partial lunar eclipse 23 Describe what is meant by ‘the dark side of the Moon’. 24 There are more extreme temperatures on the Moon than on the Earth. Propose a reason why.

242

25 Describe how the duration of a lunar eclipse would be different if the Earth was smaller.

[ Extension]

UNIT

8. 4 Hint: Look at Figure 8.4.8.

Investigate

Analyse 26 Copy Figure 8.4.9, and show where the Earth would be placed if a ‘quarter Moon’ is to be seen.

1 Produce a poster of the Moon, showing the names of some major features. 2 Investigate what ‘neap’ and ‘solar’ tides are. 3 Obtain a tides chart and produce a key to explain its use.

Surf

sunlight

Moon

Fig 8.4.9 27 The tidal bulges are missing from Figure 8.4.10. Copy the diagram and include them.

Moon

4 Construct a model of the Lunar Prospector that discovered ice on the Moon by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 8, and clicking on the destinations button.

Creative writing Due to overpopulation on Earth, a settlement is to be established on the Moon. You are a consulting scientist involved in planning and establishing the colony. What requirements will people have on the Moon? Anticipate some of the difficulties of life on the Moon. Consider factors such as food, temperature, oxygen, etc. and the possibility of meteorite strikes. Include a diagram of planned lunar constructions.

Earth

Fig 8.4.10

243

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The Moon

UNIT

8. 4 Prac 1 Unit 8.4

[ Practical activities ] Crater formation

Phases of the Moon

Aim To investigate how craters get their shape

Aim To construct a flip book to show the main phases of the Moon

Equipment Flour, chocolate icing sugar, shallow tray (e.g. foil tray), three rocks about 1 cm to 7 cm, newspaper, metre rule

Method

Prac 2 Unit 8.4

Method

1 Record the phases of the Moon every third night for one month, using multiple copies of a record box like the one in Figure 8.4.12.

1 Spread newspaper under the shallow tray. 2 Place a fairly thick layer of flour in the tray, and smooth it into the tray. 3 Cover this with a thin layer of chocolate icing sugar to represent an outer layer of rock. 4 Drop the rocks onto the flour from a height of 1 metre. Remove them after each drop. 5 Increase the height to two metres and repeat. 6 Record the diameter of each crater and its shape for the three rocks. CAUTION: Do not dispose of the flour down the sink (your teacher will advise you of the correct method of disposal).

Date

____________________

Time ____________________

Fig 8.4.11

Fig 8.4.12

Moon view record box

2 If the sky is cloudy, guess what the Moon may look like. 3 Paste the diagrams onto stiff cardboard. 4 Place them in order from a new moon and secure to make a small booklet. 5 Flip the pages with your thumb to see the Moon’s phases.

chocolate icing sugar

flour

Questions 1 Make a list of the factors that affected the type of crater formed. 2 Did the same rock make the same size crater every time? Explain. 3 The experiment assumes that all objects hit planets or moons vertically. Design an experiment to see the effect of an impact at an angle.

244

Chapter review [ Summary questions ] 1 Give scientific definitions of the terms ‘day’ and ‘year’. 2 Identify the term used when day and night are of equal length. 3 Identify the word starting with L that is used to describe aspects of the Moon. 4 State how long it takes the Moon to orbit the Earth. 5 Describe gravity on the Moon. 6 Draw the eight main phases of the Moon. 7 Explain three examples of our dependence on the Sun. 8 Copy and complete: Nuclear _____ reactions occur in the core of the Sun. 9 Why do sunspots appear dark when they are obviously very hot? Explain. 10 List the planets in order, starting with the one closest to the Sun. 11 Describe one aspect or fact about each planet. 12 Identify two space probes and state which planet(s) they explored. 13 Identify the planet that has an orbit which overlaps that of another.

[ Thinking questions ] 14 Explain the differences between a prominence and a solar flare. 15 Use a diagram to describe what causes an aurora. 16 Draw a diagram to demonstrate an annular eclipse. 17 State whether the year 2500 is a leap year. 18 The geocentric model was accepted before the heliocentric model. Compare these two models of the solar system. 19 Classify the following as supporters or opponents of the heliocentric solar system model: Aristotle, Copernicus, Ptolemy, Brahe, Kepler. 20 Explain why scientists did not speak up in favour of the heliocentric model for a long time when they knew it to be a better model than the geocentric model. 21 Identify the astronomer who first used a telescope to find errors in the geocentric model.

22 Explain the following phenomena. Include a description of what each phenomenon is and what its cause and effect are. Give examples where appropriate. a tides b seasons c day/night d year e lunar eclipse f solar wind 23 Describe how many cultures depend on the Sun and Moon for survival.

[ Interpreting questions ] 24 Use the ‘fact files’ in this chapter to answer the following questions. a Identify the planets with more than 15 moons. b List the terrestrial planets. c Identify the planets that have methane in their atmosphere. d Identify the planet that is most similar to Earth and explain your reasons for choosing this planet. e State how long a day and a year are on Pluto. f Identify the planet that looks red and explain why this is the case. 25 Construct a table that shows the distance from the Sun, the day length and the year length for each planet. 26 a List the things that make it possible for us to survive on Earth. b Could any other planets in the solar system support life? Explain why. c Which planet would be easiest to move to if we had to leave the Earth? Explain why. d Of the nine planets and the Sun, evaluate which is the most important body in the solar system. Give reasons for your decision. Worksheet 8.4 Earth and space crossword Worksheet 8.5 Earth and space revision Worksheet 8.6 Sci-words

245

Our planet Earth Key focus area:

>>> The implications of science for

4.4, 4.5, 4.9.3, 4.9.4, 4.9.5, 4.9.6

Outcomes

>>>

society and the environment Current issues, research and developments in science

By the end of this chapter you should be able to: identify and describe the different layers of the Earth and its atmosphere describe where sedimentary, igneous and metamorphic rocks come from identify different rocks and the minerals that make them up describe how rocks are broken down and moved about, and how this affects the shape of the land identify gases found in the atmosphere and describe their importance to life on Earth describe the importance of ozone and greenhouse gases to life on Earth describe the effect of the Sun on the atmosphere, weather and the water cycle

Pre quiz

identify some specialised careers for scientists.

1 If we dug a hole to the centre of the Earth, what would we see?

2 What causes volcanoes and earthquakes? 3 Is it possible for rocks to be made out of dead animals?

4 What is acid rain and what damage can it cause?

5 What is the danger in having a hole in the ozone layer?

6 Name a type of scientist who works with rocks or the atmosphere.

>>>

9

9.1 UNIT

UNIT

context

9.1 In 1872 Jules Verne wrote a best-selling novel called A Journey to the Centre of the Earth, in which dinosaurs fought to the death deep inside a hollow Earth. Today geologists are still trying to finding out what actually goes on inside our Earth. Geologists ask us to imagine the Earth as a cracked hard-boiled egg. The thin, cracked shell is the ‘crust’ and is divided into plates; within the shell is the ‘mantle’ made of firm but

Journey to the centre of the Earth Let’s now take an imaginary journey with a geologist to the centre of the Earth. A cutaway view of the Earth showing the different layers

Fig 9.1.1 Lithosphere p (crust and upper mantle)

Crust 11–70 km thick

slippery egg white, and the solid yolk is the ‘core’. As you move the pieces of shell around, some mantle is exposed. The same thing happens on Earth but this movement causes mountains, earthquakes and volcanoes.

The crust The crust is the layer of Earth on which we live. It contains the land and seas. If we were to dig down into the crust the first thing we would come across is a thin layer of soil and sand. This is followed by a layer composed mostly of solid rock. Just like the shell of an egg, it is brittle and can easily break. On Earth there are 12 major ‘pieces’ or plates. The crust is thickest under the continents (about 70 km thick) and thinnest under the sea (about 11 km thick). The crust is extremely thin when compared to the diameter of the Earth—like a postage stamp stuck on a basketball. The temperature of the crust increases from an average of 20°C at the Earth’s surface, Prac 1 to about 500°C at its maximum depth. p. 250

The mantle Mantle 2900 km

Solid

Inner core

Core

5100 km

6378 km

On further digging we enter the mantle. It is about 2900 km thick, with temperatures of 500°C near the crust and 3000°C nearer the core. The mantle is unusual in that the upper mantle is solid, very much like the crust. The upper mantle and crust form a rigid layer of rock called the lithosphere (from lithos, Greek for stone). Geologists believe that below the lithosphere is a narrow layer of semi-molten rock called the asthenosphere (from asthenes, Greek for weak). Below this is the lower mantle, which is solid due to the extreme pressure from the material above.

The core At the centre of the Earth is the core. The core is actually made up of two parts, a 2200 km thick liquid outer core and a 1280 km thick solid inner core.

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Our Earth The outer core is made of continually moving molten (molten means melted) metal (iron and nickel). This metal gives the Earth its north and south poles and its magnetic field. This field acts as a ‘cosmic shield’ for the Earth, protecting us by deflecting large doses of cosmic rays from the Sun. The temperature of the outer core varies from 4000 to 6000°C. The remaining 1280 km of our journey is through the inner core, where temperatures range from 4000°C to 7000°C. At these temperatures the iron and nickel that make up the inner core should be molten, but the extremely high pressures from the layers above keep these metals solid. Worksheet 9.1 Cut-away Earth

Crashing plates The surface of the Earth looks as if it could never move, but bits of it are actually moving all the time. The lithosphere is broken into huge slabs of rock called plates. These plates ‘float’ on the semi-molten rock of the asthenosphere. Currents (called convection currents) in the asthenosphere slowly move the semi-molten rock and also carry the plates

along with it: the plates are continually moving. The plates A changing Earth move until they eventually crash A map of the world of into one another, break away the distant future would look very different to from each other or slip along or that of today. Because under each other. This is the the continents are on source of much volcanic activity shifting plates, they are travelling slowly across and earthquakes. the surface of the Earth. This sliding is not smooth: Australia is drifting north rocks stick and jam. Pressure at about 5 cm per year! The Mediterranean Sea builds until the rocks can take is slowly being squeezed no more. There is a sudden shut, the Atlantic Ocean explosive slippage and an is getting wider and the earthquake happens, its damage Himalayan mountains are getting higher! being the most severe at the edges of the plate. Shifting plates also suggest that the continents must be slowly moving too. When a German meteorologist, Alfred Wegener, suggested in 1912 that continents could shift, the idea sounded so ridiculous that it was hardly believed at first. There are clues, however, that the continents were once stuck together as super-continents and that they have slowly shifted Earth’s plates move in different directions as they split, bang and scrape together.

Fig 9.1.2

North American plate

Eurasian plate

Caribbean plate Philippine plate

African plate

Cocos plate

Pacific plate

South American plate

Indian–Australian plate

N W

Nazca plate

E S

collision boundaries spreading boundaries

248

movement not known transform boundaries

main movement directions

to their current positions. These clues include the shapes of the continents and the types of rocks and plant life found on them. The idea that the Earth’s lithosphere is made up of shifting plates was first introduced in 1969 and is called the theory of plate tectonics.

UNIT

9.1 e the outer and inner core f the outer and inner mantle g the lithosphere and asthenosphere

Crashing plates 6 Copy and complete: The ____________ is broken into huge slabs of rock called __________. These ___________ ‘float’ on the continually moving molten rock of the _______________. 7 Identify two events that are caused by the plates of the Earth crashing into each other or moving apart. 8 Describe how an earthquake may be caused.

Think 9 List the types of places where a geologist may work. 10 Describe two tasks that a geologist would do as part of their work. 11 If you were to be good geologist, describe what skills you would need to have. 12 Explain why a geologist would need to check the land and rock that a skyscraper is to be built on.

Fig 9.1.3

UNIT

9 .1

The edge of a tectonic plate: the San Andreas fault causes up to five tremors a day through California.

[ Questions ]

Checkpoint Journey to the centre of the Earth 1 Clarify what is meant by ‘the crust of the Earth’. 2 Identify where the crust is: a thickest b thinnest 3 List the layers of the Earth from inside to out. 4 Identify which of the layers of the Earth is: a the thickest b the hottest c mainly made of iron and nickel d liquid e solid 5 Draw a cut-open diagram of planet Earth and label: a the poles b the equator c the direction it spins d the crust

13 Copy the following and modify any incorrect statements so they become true. a The inner core of the Earth is solid. b The iron and nickel in the crust gives the Earth its magnetic field. c The crust is very thick compared to the total volume of the Earth. d Mines are often deep enough to go into the mantle. 14 Describe how life on Earth would be affected if there was no magnetic field. 15 Scientists want to explore the Earth’s structure by digging a hole through the crust into the mantle. List the advantages and disadvantages of choosing central Australia for the dig.

Skills 16 Use the information in the table to plot a line graph showing the temperature for every kilometre as we dig into the crust.

Depth (km) Temperature (°C)

0

2

4

6

8

20

87

153

220

286

17 Use your graph from question 16 to estimate the temperature at the following depths: a 1 km c 10 km b 5 km d 20 km

>> 249

>>>

Our Earth

18 Use the graph to roughly determine the depth at the following temperatures: a 50°C c 200°C b 100°C d 300°C 19 Use an atlas to find the spot on Earth where you would expect the crust to be: a thickest b thinnest c thinnest while you are still standing on land. Explain why you chose these three sites.

3 a Research and write a short report on how the journeys of these sailors assisted us in thinking the Earth was spherical: i Christopher Columbus in 1492 ii Magellan and his ship Victoria in 1519 b Compare what they found to the work done by Eratosthenes of Cyrene in about 250 BC. 4 Australia is drifting northwards at 5 cm per year. This means that Sydney will eventually be where Newcastle is now! Calculate how long this will take if the distance between Newcastle and Sydney is 100 km.

[ Extension] Investigate 1 Imagine digging a hole from where you live straight through Earth to the other side. Use a globe to predict where the tunnel would emerge. 2 Investigate the seven continents of the world and identify the highest mountain on each.

UNIT

9 .1

Creative writing It’s hot down here! You have invented a machine that will dig 100 km into the centre of the Earth every day. The journey will take a little over two and a half days. Write a series of four diary entries for the time of day that you enter a new layer of the Earth. Calculate how long it will take to get through each layer and describe the conditions found in each.

[ Practical activity ] The crust is like an eggshell

Prac 1 Unit 9.1

Aim To observe first-hand a model of the Earth’s plates Equipment Fresh hard-boiled egg

Method 1 Tap the egg firmly so that the shell cracks, but do not peel off the shell. 2 Squeeze the egg gently but not enough to destroy the egg. 3 Try to slide one piece over another.

Fig 9.1.4

The cracks are in the egg’s shell only.

Questions 1 Describe what happens to the cracks in the shell. 2 Record your observations. 3 Explain how this cracked egg is similar to the Earth.

250

4 If an ant was standing on one of the cracks while you were performing the experiment, describe what it would experience.

UNIT

context

9. 2 Rocks may not be alive, but they can still tell us quite a lot. Geology is the study of the Earth, including its rocks and minerals. Though we are familiar with the words ‘rock’ and ‘mineral’, not many of us can give a good definition of what each word really means.

Minerals Clare describes minerals as ‘the building blocks of all rocks’. Clare’s work as a mineralogist involves working with mining companies to find better ways to get the minerals out of rocks. Minerals are natural substances in which the particles are arranged in patterns. Minerals often occur in beautiful shapes called crystals. Metals, gems and industrial materials of many kinds are made from minerals. Examples of minerals are quartz, mica and feldspar as seen in Figure 9.2.1. Ninety-nine per cent of all minerals are made up of only eight elements—oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium. Since the two most common elements that make up the Earth are oxygen and silicon, it is not

Fig 9.2.1

First we will ask Clare, a mineralogist, to explain what minerals are. We will then ask Peter, a petrologist, to explain rocks and their formation.

surprising that these are also common in minerals. Quartz is made up of silicon and oxygen. Some minerals are made up of only one metal element such as gold, silver or platinum, and are called native metals.

Native silver

Fig 9.2.2

Piezoelectricity When two brothers, Pierre and Jacques Curie, sandwiched a thin slice of quartz between two layers of tin and applied pressure to it in 1880, they detected a short pulse of electricity. Many years later, scientists realised that this so-called ‘piezoelectricity’ could be generated using tiny quartz crystals, and could be used to keep time in watches and clocks.

Quartz (left), mica (middle) and feldspar (right) are all minerals.

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Rocks and minerals Characteristics of minerals When asked how we can identify minerals, Clare suggested that we look at several properties or characteristics. These are described below. Hardness is an important property of minerals. A mineral is harder than another if it can scratch it, without getting scratched itself. In 1812, an Austrian mineralogist, Frederic Mohs, invented a scale of hardness from 1 to 10, 10 being the hardest and 1 being the softest. A mineral can scratch another only if it is higher on Mohs’ scale. Mohs’ scale of hardness 1

Talc

2

Gypsum

3

produce a streak, while other powdered minerals have a different-coloured streak than the mineral itself.

Minerals used by Aboriginal artists Powdered minerals are used by various native tribes worldwide as decorations and paint materials. The Australian Aboriginals collect their minerals as weathered (broken down) rocks. These minerals are called ochres and are crushed to a powder by the artists using a grindstone. The following table shows some of the ochres (minerals) used in Australia.

Hardness of some common objects Fingernail

2.5

Copper coin

3.5

Calcite

Iron nail

4.5

4

Fluorite

Glass

5.5

5

Apatite

Steel knife

6.5

6

Orthoclase

Emery board

9.5

7

Quartz

8

Topaz

9

Corundum

10

Diamond

A dentist’s drill has diamond pieces on its surface.

Fig 9.2.3

Name of ochre

Colour of streak

Where ochre is collected

Haematite

Red

Found as pebbles

Kaolin

White

In creek beds

Limonite

Yellow (or brown)

Water-worn pebbles in creek beds

Charcoal

Black

Produced in fires

Different colours in minerals are caused by the different chemicals in them. The red colour of haematite, for example, is caused by lots of iron oxide (more commonly known as rust). These ochres are often mixed to make other colours.

Fig 9.2.4

Although a mineral may have a distinctive colour, this is not a reliable enough property to identify the mineral. A better method is to crush the mineral into a powder. The colour of a powdered mineral is called its streak and can often be seen by rubbing a mineral on an unglazed white tile. Some minerals do not

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Aboriginal rock painting using powered ochre supplied by nature

Colours of the body The colours used by the Aboriginals often had special meanings. For some the och res represented the colours of the body. White is the colour of bones, brown is the colour of skin, red is the colour of bloo d (a sacred colour) and yellow is the colour of body fat.

Charcoal, for example, is commonly mixed with kaolin to make grey. The powders are also mixed with egg, juice or blood to make a paste that can then be painted onto rocks or the body.

Crystals Many minerals have a distinctive crystal structure. The word ‘crystal’ comes from the Greek word kyros, meaning icy cold. In ancient times it was believed that quartz crystals were composed of water that had frozen so solid that it could never melt. Because each mineral has a different crystal structure and colour, they reflect light differently. Lustre is a term that refers to the way a mineral reflects light.

Fig 9.2.5

Some common uses of minerals are listed here. Mineral

UNIT

9. 2 Uses

Salt

Food preservative, source of sodium and chlorine

Graphite

‘Lead’ in pencils, electric motors

Phosphate

Matches, fertilisers

Tungsten

Light bulb filaments, saw blades and drill bits

Sulfur

Used to make sulfuric acid, fertiliser

Rocks Petrology is the study of rocks. Prac 1 Prac 2 As a petrologist employed by a p. 255 p. 255 mining company, Peter collects rock samples, looking at their properties and working out which minerals they contain. This information is used in designing mines. Peter describes rocks as follows: ‘Rocks are made up of minerals. Granite is a rock made from three minerals—quartz, mica and feldspar—whereas limestone contains just one mineral—calcium carbonate. You may be surprised to learn that clay and sand are types of rock.’

The distinctive flat crystals of wulfenite

Some crystals have an internal structure that causes them to break apart more easily in particular directions. These are called cleavage planes. Several cleavage planes can be seen in these crystals.

Fig 9.2.6

Granite is made up of quartz, mica and feldspar.

Fig 9.2.7

Ores Part of Peter’s job is to study the minerals in rocks and work out whether it is worthwhile getting them out. Ores are rocks or minerals that contain elements that can be profitably extracted. For example, iron is extracted from an ore called haematite, and aluminium from the ore bauxite.

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Rocks and minerals Haematite (iron ore) occurs in several forms, including so-called kidney ore.

UNIT

9.2

Fig 9.2.8

Ore

Element that may be extracted

Azurite

Copper

Bauxite

Aluminium

Carnotite

Uranium

Cassiterite

Tin

Chalcopyrite

Copper

Galena

Lead

Haematite

Iron

[ Questions ]

Checkpoint Minerals 1 Describe what a geologist does. 2 Clarify what minerals are. 3 List four examples of minerals 4 List four characteristics of minerals. 5 a Explain what Mohs’ hardness scale is used for. b Frederick Mohs was a scientist. Identify what type of scientist he was.

Rocks 6 Describe what a petrologist does. 7 Clarify the term ‘rock’. 8 Identify three examples of rocks.

Ores 9 Is an ore a rock, a mineral or could it be either? 10 Clarify the term ‘ore’. 11 Identify the ore that contains: a iron b aluminium 12 Identify two ore types that contain the same element. Name the element.

Think 13 Explain the difference between geology and petrology. 14 Explain how a native mineral is different from most other minerals. 15 Identify how ancient or current-day people use pigments from minerals. 16 Describe what ochre is, and who uses it. 17 Identify three ochres and their colour.

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Some other examples of ores are listed in the table below. Australia has large mines for extracting aluminium, iron, uranium and many other elements from rocks.

18 Explain how an ochre is prepared before being used for painting. 19 The following statements are incorrect. Modify each so it becomes true. a A mineral is any substance found in the ground. b The two most common elements that make up the Earth are oxygen and aluminium. c Gold and silver are metals, not minerals. d Mineralogy is the study of minerals. 20 Silicates are types of minerals containing silicon and oxygen. Explain why silicates are very common. 21 True or false? a Clay is a type of rock. b A rock may contain only one type of mineral. c Ore is a type of mineral.

Analyse 22 a Construct a line representing Mohs’ scale of hardness. b Predict where each of the following would go on the line and mark them on it. i fingernail ii copper iii iron nail 23 List the following minerals in order from softest to hardest. apatite, calcite, talc, quartz, diamond 24 Predict whether: a orthoclase would scratch gypsum b quartz would scratch topaz c calcite would scratch your fingernail d diamond would scratch glass 25 Gneiss contains feldspar, quartz, mica and hornblende. Identify which of these: a are minerals b is a rock

UNIT

9.2 [ Extension ] Investigate 1 Investigate the types of gemstones, their characteristics and where they are found. 2 The term ‘carats’ is used to describe diamonds and other gems. Investigate exactly what a carat is, and find out how diamonds are classified in terms of colour and quality. Produce an information card for people to use when selecting diamonds for jewellery. 3 Research the location of Australia’s major known mineral deposits. Draw a poster-sized map showing the location of these. Include pictures of different minerals, ores and mines in Australia.

UNIT

9.2

4 Present information in a chart showing how an ore is processed to produce a pure metal.

Surf 5 Learn more about the uses of minerals in Australia, by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9, and clicking on the destinations button.

[ Practical activities ] Fig 9.2.9

Making a crystal icy pole stick

Aim To grow a crystal and observe its structure Prac 1 Unit 9.2

Equipment Copper sulfate, 250 mL beaker, icy pole stick, petri dish, Bunsen burner, tripod, gauze mat, heat-proof mat

seed crystal

Method copper sulfate solution

PART A Obtaining a seed crystal 1 One-third fill a 250 mL beaker with water and dissolve as much copper sulfate in it as possible. 2 Heat the solution and add more copper sulfate in small amounts until no more will dissolve.

2 Sketch the fully grown crystal.

3 Remove the solution from heat and allow it to settle and cool for about 5 to 10 minutes.

3 Identify whether copper sulfate crystals have obvious cleavage planes.

4 Carefully decant some of the solution into a shallow layer in a petri dish and allow this to cool overnight. Keep the rest of the solution in the beaker. PART B Growing a large crystal 1 Obtain a small ‘seed’ crystal from the petri dish (or ask another group for one if yours did not produce any). 2 Tie it to a length of cotton thread and suspend it in your cooled copper sulfate solution. 3 Observe the crystal every few days for a week or so.

Observing rocks Prac 2 Unit 9.2

Aim To examine the characteristics of various rocks and minerals Equipment A selection of rock and minerals, copper coin, steel nail, unglazed white tile

Method

Questions 1 Your initial solution was saturated. Explain what this means.

Construct a table of results and comment on as many of the following characteristics as you can for the rock samples: colour, streak, lustre, crystal structure, hardness, density.

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UNIT

context

9. 3 When you pick up a rock, have you noticed that some are different than others? There are so many different rocks that geologists have found it hard to classify them. To make identification of rocks easier, geologists classify rocks according to how they were formed. This results in three main types of rocks: igneous, sedimentary and metamorphic.

Igneous rocks Igneous rocks are formed when molten material from within the Earth cools and becomes solid. Igneous comes from the Latin word ignis, meaning fire. Molten material is called magma when it is below the Earth’s surface, and lava when it is above the Earth’s surface. Magma reaches the Earth’s surface when volcanoes erupt. When magma cools slowly below the Earth’s surface, intrusive igneous rocks containing large interlocking crystals are formed. Intrusive means ‘forced in’, and is a good description of underground igneous rocks that have squeezed between other rock layers. Lava solidifying to form extrusive igneous rock

volcano lava extrusive igneous rock

dyke sill intrusive igneous rock

Fig 9.3.1

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magma

How extrusive and intrusive igneous rocks are formed

Fig 9.3.2

Granite is an example of a slow-cooling igneous rock in which crystals are easy to see. Because it is above the Earth’s surface, lava cools more quickly than underground magma and the crystals formed are smaller or nonexistent. This results in extrusive igneous rocks. Extrusive means ‘pushed out’. Basalt is an example of an extrusive igneous rock containing tiny crystals and is the main rock forming the ocean Prac 1 crust. p. 263

Uses of igneous rocks

Sedimentary rocks

Because they are hard, igneous rocks like granite and basalt are useful building materials.

Sedimentary rocks derive their name from the Latin words sedimentum, meaning ‘settling’, and sedere, meaning ‘to sit down’. They are made from sediment—small, broken-down bits of other rocks, or animal or plant remains. This material has been compressed and stuck together in a process known as lithification. There are two main stages in lithification. First, sediment builds up in a layer (for example, at the bottom of a river bed or the sea). The pressure of material above it squeezes the sediment at the bottom of the layer. This pressure reduces the air gaps and the particles interlock. Second, water seeping through the compressed sediment carries with it minerals which cement the sediment particles together even more strongly.

Uses of granite

Uses of basalt

Bridges

Bridges

Buildings

Buildings

Kitchen benchtops

Crushed and placed under railway sleepers

Gravestones

Crushed and covered with tar to make bitumen roads

Ancient tools Aboriginals had a great knowledge of the rocks in Australia. This was important in the making of tools, weapons and ochres. Different rocks were identified for different purposes depending on their hardness, ability to flake and form sharp edges, ability to be ground or worn, and their colours. Very hard igneous rocks were suitable for making tools such as axe heads. At Mount William in Victoria, volcanic greenstone was mined for axes. It had the hardness, toughness and fine grain needed to make heavy-duty axes with a sharpened edge. Greenstone from such quarries was traded with many other tribes around Australia. Axes made from igneous rocks have also been found in ancient Aboriginal quarries near volcanic outcrops in Kakadu National Park, Northern Territory. These axes have been dated using scientific methods and found to be over 20 000 years old! An Aboriginal axe-head made from an igneous rock

Sedimentary rock

Made from

Sandstone

Sand

Mudstone

Mud

Conglomerate

Particles of different sizes

Limestone

Remains of sea organisms (e.g. fish, corals)

Chalk

Skeletons of tiny sea animals

Coal

Compressed plant material

UNIT

9.3

Fig 9.3.3

Sandstone

Fig 9.3.4

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Types of rocks

Fig 9.3.8

These stalactites are chemical sedimentary rocks.

Stalactites and stalagmites Fig 9.3.5

The Three Sisters in the Blue Mountains National Park—note the horizontal sedimentary rock layers

The white cliffs of Dover in England are made of powdery chalk composed of the tiny skeletons of sea creatures over 70 million years old. The white cliffs of Dover, England

Fig 9.3.6

Sedimentary rocks are easy to split because of their layered structure. Sandstone comes in a variety of colours, and blocks of it are used to make bridges and buildings. Limestone may be ground to make cement, which in turn is a key ingredient in concrete, one of the most important building materials of all. Coal is burnt to provide power for electricity generation and heating.

Kata Tjuta, meaning ‘many heads’ in the local Anangu language

Tourist-attracting rocks Kata Tjuta (the Olgas) are a group of thirty or so huge rocks in Central Australia that are the weathered remains of sedimentary rocks. They consist of both sandstone and conglomerate rock. The largest of these rocks reaches 546 metres above the surrounding ground level.

258

These fascinating natural structures are formed when slightly acidic rainwater dissolves calcium carbonate (lime) out of sedimentary rock. This lime solution may then drip from the roof of a limestone cave, leaving deposits on the ceiling (stalactites) and floor (stalagmites) when the water evaporates.

Prac 2 p. 263

Fig 9.3.7

Oyster mortar The first white settlers of Sydney had no limestone from which to grind lime for mortar used in bricklaying. Instead they collected oysters, which were in abundance around Sydney harbour, and burned and crushed them to produce the lime needed.

Career profile Palaeontologist A palaeontologist examines, classifies and describes animal and plant fossils found in sedimentary rocks. This helps us understand the history of life on Earth, which is particularly important in oil exploration.

A palaeontologist with a fossilised dinosaur skull

• • • • •

• • • •

Sedimentary, igneous or even metamorphic rocks may be changed by heat, pressure or a combination of both within the Earth. A rock made this way is stronger than the original material, because its particles are fused together. This is similar to the process of squeezing a snowball to make it stronger. Original rock

Original rock type

Changed by

Metamorphic rock

Limestone

Sedimentary

Heat

Marble

Granite

Igneous

Heat, pressure

Gneiss

Shale

Sedimentary

Pressure

Slate

Slate

Metamorphic

Heat, pressure

Schist

Schist

Metamorphic

Heat, pressure

Gneiss

UNIT

9.3

Fig 9.3.9

Palaeontologists can be involved in: locating sites where fossils may be found carefully digging fossils out of the rocks in which they are found preparing fossils for display or storage dating fossils to work out their age using information about fossils to study other things such as oil exploration or the history of life on the Earth. A good palaeontologist will: be able to work safely as a team member or alone be able to work very carefully and patiently as it can take years to remove fossils from rocks have a good eye for detail love fossils.

Metamorphic rocks Pressure cooker conditions deep in the Earth’s crust can change rocks into new types of rocks. The word ‘metamorphic’ comes from the Greek words meta (meaning change) and morphe (meaning form), so a metamorphic rock is one that has changed form.

Fig 9.3.10

Gneiss (pronounced ‘nice’) is a metamorphic rock that frequently contains bands of different minerals. Bends in the bands indicate where enormous pressure has folded the rock.

Marble is a popular material for kitchen benchtops and ornaments because of its beautiful patterns and dense composition. The Taj Mahal in India is made of the metamorphic rock marble inlaid with gemstones. Slate is used for roofing tiles, floor tiles and billiard tabletops.

In the barrel of a gun In the late 1700s, geologists Sir James Hall and James Hutton set out to prove that heat and pressure could change limestone to marble. They sealed some limestone in a gun barrel and roasted it over a fire. When they examined the contents later, the limestone had indeed turned to marble.

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Types of rocks

Fig 9.3.13

Simplified rock cycle

Igneous rocks

g

g Coolin

Meltin

Weathering Erosion

Heat Pressure

Magma

Melting Sediments

Fig 9.3.11

The rock cycle If sedimentary and igneous rocks have been changed continually into metamorphic rocks during Earth’s history, shouldn’t rocks today be mostly metamorphic ones? The answer is no, because rocks, including metamorphic ones, change back into other types because of other influences such as weathering, erosion or melting, in what is known as the rock cycle. Fig 9.3.12

Weathering Erosion

The Taj Mahal in India is made of white marble and was built by the emperor Shah Jahan as a tomb for his wife, Mumtaz. Compaction and cementing

Weathering Erosion Heat Pressure

Metamorphic rocks

Sedimentary rocks

Worksheet 9.2 Identifying rocks

The rock cycle sediments fall to the bottom of rivers and oceans

weathering breaks down rocks, erosion occurs

ocean crust

mantle sediments build up and compact to form layers of sedimentary rock continental crust igneous rocks formed from molten rock

260

heat and/or pressure form new, metamorphic rocks

sediments pulled deeper by movement of tectonic plates

UNIT

9.3 Career profile Geologist Geologists study the composition and structure of the Earth. This allows them to locate materials and minerals. Geologists work in laboratories and in the field, usually as part of a team. Fieldwork can involve spending time in remote deserts, or in tropical or Antarctic areas.

• •

Geologists can be involved in: advising on suitable locations for tunnels and bridges examining rock samples using electron microscopes studying the nature and effects of natural events like weathering, erosion, earthquakes and volcanoes taking rock samples for analysis finding the age of rocks and fossils.

• • •

A good geologist will be able to: work as a team member or alone keep accurate records and prepare reports work safely in a number of different environments.

[ Questions ]

Checkpoint Igneous rock 1 Clarify the meaning of the Latin word ignis. 2 Compare the following terms: a magma and lava b intrusive and extrusive rocks c a dyke and a sill 3 The rate of cooling of molten rock affects crystal formation. Explain how this occurs and identify whether fast or slow cooling forms the biggest crystals.

11 Copy and complete Figure 9.3.15, which is a schematic diagram summarising the rock cycle.

>>

Fig 9.3.15 igneous rocks

Sedimentary rocks 6 Identify two types of sedimentary rocks and describe what they are made from.

er o n

5 Describe a use for a particular igneous rock.

Rock cycle

sio

4 Identify two types of igneous rocks.

10 Marble is sometimes used to make food-cutting boards. Propose a reason why marble is used for this purpose.

heat/pressure

melting

7 The particles in a sedimentary rock have to stick together. Explain two ways in which this can occur. ero

e

s

he

ur

ng

lti

9 Identify two types of metamorphic rocks, and name their ‘parent’ rocks.

me

8 Identify two things that may affect rocks in the Earth’s crust.

io

n

Metamorphic rocks ss

UNIT

9.3

Fig 9.3.14

Geologists studying sedimentary rock layers in the field

me ltin g co oli ng

• • •

at/

pr

e

261

Types of rocks

Think 12 Copy and complete: Rocks are classified according to … 13 Granite is formed underground, yet granite boulders are often seen above ground in many areas of Australia. Explain how this could happen. 14 State the age of some ancient Aboriginal axes found in Kakadu National Park. 15 Draw a sketch explaining the difference between a stalactite and a stalagmite. 16 Stalactites and stalagmites often occur in pairs. Propose a reason why you think this may occur. 17 Clarify the meaning of these terms: a sediment b lithification 18 Although coal is made from plant material, a lump of coal burns much longer than a similar-sized piece of dry plant. Explain why. 19 Write a one-sentence summary of each of the three main rock types.

Analyse 20 Classify the following types of rocks from their descriptions and attempt to name each rock. a Commonly known as bluestone, this rock has small crystals and is found where volcanoes used to be in New South Wales. b Used for tiling floors, this rock easily breaks into layers. c This rock is white and made up of the remains of millions of sea creatures. d Formed inside the Earth by heat and pressure, this rock has layers of minerals that are visible. e This rock forms where muddy rivers flow into lakes. f This rock has large, easily seen crystals and forms inside volcanoes. g This rock was mined by Aboriginal people and used for axe heads.

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>>> [ Extension ] Investigate 1 a Investigate Uluru (formerly known as Ayers Rock) to find out the type of rock it is made of. b Draw a diagram to demonstrate how Uluru was formed. c Describe the cultural history of Uluru and its mythology to the Australian Aboriginals. d Discuss with your teacher how to present your findings. 2 Investigate in more detail how coal is formed, and explain the difference (besides colour) between brown and black coal. Present your information as a poster including the key stages in coal mining. 3 Investigate the properties of artificial sedimentary rocks made from various combinations of sand, dry clay, small stones, plaster mix and water.

DYO

Create 4 Imagine you are a piece of magma in a volcano. Write and draw a picture storybook that shows what happens to you as you erupt from the Earth and form a rock. Follow your life through the rock cycle as you become different types of rock.

Surf 5 View animations of how the main types of rock are created, and learn more about the rock cycle by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9, and clicking on the destinations button.

UNIT

9.3

UNIT

9.3 [ Practical activities ] Crystals and cooling rates Prac 1 Unit 9.3

Aim To observe the effect of cooling rates on crystal size

Concrete evidence Prac 2 Unit 9.3

Concrete is made from a combination of two or more of the following: cement, sand, crushed rock, water.

Aim To make various types of concrete

Equipment Copper sulfate, two 100 mL beakers, two 500 mL beakers, one 250 mL beaker, stirring rod, Bunsen burner, tripod, gauze mat, heat-proof mat, safety glasses

Equipment

Method

Method

1 One-quarter fill the 250 mL beaker with cold water, and dissolve as much copper sulfate in it as possible. 2 Heat the solution and add more copper sulfate in small amounts until no more will dissolve. You now have a saturated copper sulfate solution. 3 Carefully place half of the solution in each of the 100 mL beakers. 4 Place one 100 mL beaker in a 500 mL beaker with some cold water as shown in Figure 9.3.16. 5 Place the other 100 mL beaker in an empty 500 mL beaker. 6 Allow each to stand overnight and pour off any excess solution from the 100 mL beakers. 7 Observe any crystals formed. Fig 9.3.16

Cement (dry, powdered), sand, finely crushed rock, plastic teaspoon, paper or plastic cups, water 1 In one cup, place 3 teaspoons of sand and 3 teaspoons of cement. Label this cup 3S, 3C. 2 In another cup, place 4 teaspoons of sand and 2 teaspoons of cement. Label this cup 4S, 2C. 3 In another cup, place 2 teaspoons of sand and 4 teaspoons of cement. Label this cup 2S, 4C. 4 In another cup, place 3 teaspoons of finely crushed rock, 2 teaspoons of sand and 1 teaspoon of cement. Label this cup 3R, 2S, 1C. 5 Now gradually add a small amount of water to the first cup and mix until you get a thick, even paste. Repeat for the other cups. 6 Leave each cup to dry overnight. 7 Devise a test for the strength of each concrete sample.

Questions

DYO

1 Explain why it was important to have the same total amount of ingredients in each case. 2 Identify which sample was strongest. 3 Identify whether you think concrete setting is a physical or chemical change. Explain why. cold water

saturated copper sulfate solution

air only

Questions 1 Describe and sketch any crystals formed in the small beakers. 2 Compare the contents of the beakers to see if there are any key differences between them. If so, describe them. 3 Explain what caused larger crystals to form.

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UNIT

context

9. 4 Have you ever wondered where soil, sand, pebbles and boulders came from? When you look very closely at them you will see that they are simply rocks that have been broken down into smaller particles. This natural process is caused by wind, water, temperature and other factors. Humans can also speed up this change through their actions, some of which can have negative effects on the environment.

Break it down The process of breaking down rocks into smaller pieces is called weathering. Once weathered, any material that is loose can be moved away by the wind, water from rain, creeks and rivers and the ice of glaciers. This movement is called erosion. The material that is washed away is called sediment and is the first step in making sedimentary rocks. Rocks seem tough but can be broken down in a variety of ways. Physical weathering (sometimes called mechanical weathering) is when rocks break into smaller pieces. Waves crashing on rocky shores break down our coasts. Dramatic changes in temperature break rock into small flakes: water expands when it freezes and can split rocks in two if it freezes in cracks on frosty nights. The small particles of soil and sand that are carried away by wind and water have an abrasive action that can act like sandpaper on other rocks that they scrape across. Farming and drought loosens the soil and can speed up erosion by the wind, as Figure 9.4.1 shows. Worksheet 9.3 The soil texture triangle

Prac 1 p. 268

Some rocks are actually changed into new substances by chemical reactions with water or the gases of the air. This is called chemical weathering. Burning fossil fuels and other industrial activity adds harmful pollutants to the air. Some of these

264

Fig 9.4.1

Extreme erosion: wind dumped 140 000 tonnes of soil from farmland on Melbourne in 1983.

pollutants are acidic and can dissolve in rainwater to form acid rain. Acid rain is a product of pollution that can speed up the process of chemical weathering. It can also have many effects on the environment, including: • dissolving statues and buildings made of certain rocks such as marble • killing fish and animals in rivers and lakes • killing forests, leading to erosion • making soils too acidic for plants and Prac 2 crops to grow. p. 268 Other weathering can be caused by animals scratching and breaking apart rocks with their tracks, as they look for food and when they build burrows. Seeds can settle and grow in small cracks in rocks, and tree roots can search out cracks for a better grip. As these plants grow so do their roots, forcing the crack wider until eventually the rock splits. Any weathering due to living things is called biological weathering.

UNIT

9. 4 Gases dissolve in water vapour and form sulfuric acid Wet deposition (acid rain) can cause die-back of new growth, leaf fall, and root damage to trees and crops. It increases soil acidity and releases poisonous chemicals into soils, lakes and rivers

Smoke and fumes from power stations and factories Sulfur dioxide (SO2)

lakes acidified

Fig 9.4.2

Dry deposition— smoke and soot blacken buildings. Sulfur dioxide corrodes metal and stone and damages plants

Sulfur dioxide in pollution causes acid rain, which will increase chemical weathering.

People and erosion

Industrial pollution adds harmful chemicals to the atmosphere.

Fig 9.4.3

Science has produced many inventions. These need to be built and fuelled, often from materials found in the Earth’s crust. Humans have changed the surface of the Earth dramatically, particularly in the past 200 years since the Industrial Revolution. We have physically broken rocks down by mining them, by using explosives, and by landscaping the Earth with roads, houses and cities. Exhaust gases from cars and factories have added destructive gases to the air. These can slowly chemically weather away rock on mountainsides and the rock used for city buildings. Building houses, roads and their cuttings, breakwaters and piers in the sea, and ploughing on farms all change how water and wind flow. Without careful planning, these changes can increase the amount of soil and sand that is washed away. The roots of trees and plant cover help to keep soil bound together and make it less likely to be eroded. Drought, overgrazing and forest clearing can remove grass and plant cover, allowing the wind and water to remove the soil.

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Weathering and erosion

Career profile Environmental scientist Science has had a large impact on our society and especially on the environment. Environmental scientists have the important job of measuring, recording and finding methods to control the harmful effects of human activity on our environment.

•

Environmental scientists can be involved in: investigating the effects of chemical spills and accidents on the environment assisting farmers, industry and others in methods to reduce their negative effect on the environment testing pollution in water, soil and air assessing the environmental impact of new housing estates and industrial developments upholding anti-pollution laws.

• • • •

A good environmental scientist will be able to: work as part of a large team communicate by writing clear, accurate reports apply the scientific method to an investigation be passionate about environmental issues.

• • • •

Environmental scientist taking a water sample to check pollution levels

Fig 9.4.4

What can we do? One of the implications of science speeding up erosion and weathering is the need to now bring it all back under control. We all need to help protect the environment. Contour ploughing (where furrows run around a hill and not down it) on farms, gutters and the sealing of roads are all used to direct water in order to minimise erosion. Livestock numbers need to be monitored, particularly in times of drought, to minimise overgrazing. Wind speed can be reduced by windbreaks and stands of trees. Models of buildings, piers and breakwaters can be used to simulate erosion and plans can be changed to minimise problems before building starts.

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Choosing to walk or ride instead of driving a car can mean that you are producing less harmful gases that will form acid rain. Modern car exhaust systems must have catalytic converters that reduce the amount of pollutants pumped into the air. New hybrid petrol/electric cars are available that produce less than half the pollution of normal cars. Industrial chimneys can have ‘scrubbers’ attached to remove some of the dangerous chemicals discharged from them and processes changed to release less harmful pollutants. There are things we can all do to help. Think about it!

UNIT

9. 4

UNIT

9. 4 [ Questions ]

Checkpoint Break it down 1 Clarify the meanings of the following terms: a soil b decomposition c weathering d sediment 2 Explain the difference between erosion and weathering. 3 Describe what happens to water when it freezes. 4 Identify three causes of: a mechanical weathering b biological weathering 5 Identify three different ways in which rocks are weathered. 6 Identify four ways in which weathered material can be moved.

16 Identify which parts of a statue are most likely to be weathered and explain why. 17 Chemical weathering is more likely in the city than the country. Explain why. 18 In your own words, summarise what an environmental scientist does. 19 Construct an argument as to why you think humans have or have not sped up erosion and weathering.

Create 20 The Environment Protection Authority (EPA) has responsibility for protecting the environment. An environmental scientist employed by the EPA gets up and watches a morning news report that there has been an oil spill in Sydney Harbour. Write a diary for their day, starting from when they hear the news.

People and erosion 7 Explain two ways in which humans and science have accelerated weathering.

[ Extension ]

8 Identify the chemical released into the air that speeds up chemical weathering.

Investigate

9 Explain how this chemical gets into the air. 10 Describe how acid rain speeds up chemical weathering.

What can we do? 11 Describe whose responsibility it is to stop the weathering caused by humans. 12 Identify two things that you can personally do, that will help stop or slow weathering and erosion.

Think 13 Compare the similarities and differences between sand and boulders. 14 It is dangerous to leave a filled glass bottle in the freezer. Explain why. 15 Many ancient statues in cities have changed shape in the past 50 years. Propose a reason why.

1 a Investigate ways of minimising erosion in one of the following situations: • in rivers • on beaches • on farms • around building or road construction sites b Use this information to go out and find examples of these methods. Take some photographs of them. c Produce a poster with your photos to show how these methods work. 2 Describe what these geographical features are and how they form. a river deltas b sandbanks and sandbars in rivers 3 Produce a crossword about weathering and erosion.

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Weathering and erosion

UNIT

9. 4 Prac 1 Unit 9.4

[ Practical activities ] You’re cracking me up!

Acid rain

Aim To investigate the effect of changing temperature on rocks

Aim To simulate the effect of acid rain on

Equipment Large tin, Bunsen burner, bench mat and matches, safety glasses, tongs, sample(s) of rock (granite, sandstone or shale)

Method

Prac 2 Unit 9.4

various rocks

Equipment Safety glasses, watch-glass, eyedropper, dilute sulfuric acid, samples of rock (limestone, marble, sandstone, shale, granite, basalt), 3 x 100 mL beakers, hammer

1 Put your safety glasses on.

Method

2 Three-quarters fill the tin with cold water.

PART 1 1 Place the rock sample on the watch-glass.

3 Hold a small piece of rock in a blue Bunsen burner flame with tongs. 4 After about a minute, carefully drop the hot rock into the water. 5 Carefully observe what happens. 6 Once cool, repeat 2–3 times with the same rock, recording your observations.

Questions 1 Identify the type of weathering you are simulating. 2 Draw a conclusion about the effect of changing temperatures on rock. 3 Explain other ways that temperature changes can crack rock.

2 Place 2–3 drops of acid on the surface of the rock. 3 Record your observations. PART 2 1 Measure out three identical samples of limestone or marble chips. 2 Use a hammer to make the particles in one pile large, another medium and the last small. 3 Place each pile in a 100 mL beaker. 4 Add the same volume of dilute sulfuric acid to each. 5 Record the time required to completely dissolve the limestone.

Questions 1 Identify the type of weathering you are simulating. 2 Draw a conclusion about the effect of acid on rock. 3 Draw a conclusion about how the size of a rock affects the rate at which it is damaged.

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UNIT

context

9. 5 We live in a thick layer of gases that surrounds the Earth. This layer is what we call ‘air’. Scientists know the layer of gases as the atmosphere. The atmosphere moves and swirls about us, often quite violently, with winds, storms, cyclones and tornadoes. It stretches about 800 km from the Earth’s surface, providing us with oxygen to breathe and clean water to drink. It also protects us from the harmful radiation from the Sun and from stray meteorites. The atmosphere is very important to all of us, and without it we would not be here.

ionosphere

120

110

100

90

80

Layer upon layer 70 mesosphere

60 Altitude (km)

Although the atmosphere can be considered to be about 800 km high, it is very thin at the top and much more dense down where we live at the Earth’s surface. Ninety-nine per cent of all the air in the atmosphere is found in the first 80 km from the surface, with little left for the remaining 700 km or so. We live in the troposphere, the layer that touches the Earth’s surface. This is where three-quarters of all air is found and where the clouds and weather occur. The troposphere has a height of about 10 to 13 km, and as you climb higher the temperature drops from an average of 17°C to –52°C. The stratosphere is the next layer and extends to 50 kilometres high, with temperatures gradually increasing to –10°C at the top. It is a region of very low air pressure and fast jet-stream winds. Most commercial aircraft fly here. Within the stratosphere is the all-important ozone layer. This blocks out almost all harmful solar radiation, which, if allowed through, could injure or kill most living things. Above the stratosphere is the mesosphere, which extends to about 80 kilometres and where the temperature again falls to –93°C. At the outer limits of the atmosphere we find the largest of the layers, the thermosphere. This is a region of increasing temperature and few air particles.

50

40

stratosphere

30 ozone 20

10

0 –100

Mt Everest

troposphere

sea level –80

–60 –40 –20 Temperature (°C)

Layer upon layer—the Earth’s atmosphere. The temperature at each level is shown as the solid curve.

0

20

40

Fig 9.5.1

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The atmosphere

2 fossil fuels: every time fossil fuels such as petrol, oil, gas and coal are burnt in car engines, factories, homes and power stations, carbon dioxide is produced 3 rotting garbage in tips breaking down to release carbon dioxide. Australians alone add 70 million tonnes (1 tonne = 1000 kg) of carbon dioxide to the atmosphere each year. Carbon dioxide is increasing in concentration.

Fig 9.5.3

360

Fig 9.5.2

Space shuttle image of the clouds and weather patterns in the troposphere

The region called the ionosphere begins near the top of the stratosphere and extends Shooting stars through the mesosphere and A shooting star is actually thermosphere, but is most a meteor: what you are noticeable at altitudes above about seeing is a small rock, 80 km. The ionosphere is also t, walnu a of size the maybe burning up 100 km or so where meteors begin to burn up above the Earth. and where harmful gamma rays from the Sun are screened out. The final layer is the exosphere, which begins at about 600 km and extends out into space.

What’s in air? The air we breathe is made up of more than ten different gases. One of the most important gases in the air is oxygen (O2). This is the gas that humans and all other animals breathe. Although only making up 21 per cent of the atmosphere, it is constantly being replaced by plants. Like animals, plants also use some of the oxygen in air to produce energy. Only a tiny 0.03 per cent of the atmosphere is carbon dioxide (CO2). It is vital to plants since they use it to make their own food. CO2 is also one of the gases animals breathe out. The amount of carbon dioxide in our atmosphere is increasing due to: 1 forest depletion: trees use up carbon dioxide and every tree that is cut down increases the amount of this gas in the atmosphere by reducing the amount removed from the air

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CO2 concetration (parts per million)

350 340 330 320 310 300 290 280 1850

1900

Year

1950

2000

At 78 per cent, nitrogen is the most abundant gas in the atmosphere. It seems to have little use except to dilute the oxygen gas to levels that animals can breathe without feeling ill. Pure oxygen can be poisonous to animals and plants. In the middle level of the stratosphere lies a 15–20 km thick layer of ozone (O3).

The greenhouse effect The Sun does not directly warm the Prac 1 atmosphere. If it did, the atmosphere would p. 275 be hotter at the top than the bottom and snow would never be found on mountaintops. The Sun actually warms the Earth, which then warms the atmosphere. The part of sunlight that we can see (called visible light) and the part of sunlight that gives us heat (called infra-red or IR radiation) pass straight through all the layers of the atmosphere. The sunlight falls on the Earth’s surface and is absorbed, heating up the rocks, water and buildings that it hits.

UNIT

9. 5 Radiation passes straight through glass instantly Radiation passes straight through atmosphere instantly greenhouse

Heat cannot escape easily through carbon dioxide so atmosphere stays warm.

Heat energy cannot escape through glass easily so greenhouse stays warm

The greenhouse

Fig 9.5.4

The atmosphere

Compare the two diagrams and you will see why it is called the greenhouse effect.

Overnight this stored heat is released slowly back into the air, warming it up. If all this heat escaped back to space, we would freeze at night. Clouds, water vapour and gases such as carbon dioxide and methane reduce this loss to space and keep the atmosphere warm. Carbon dioxide is very effective in trapping this heat. This greenhouse effect keeps the Earth at a temperature that can support life. It is a natural and essential phenomenon. The enhanced greenhouse effect is caused by an increase in the amount of carbon dioxide (and some other pollutant gases) in the atmosphere. The amount of CO2 in the atmosphere has increased by 37 per cent since the early 1800s. Many scientists believe that this increase has led to a warming of the Earth— global warming. Glaciers have been gradually retreating (melting and getting smaller), huge icebergs are breaking off Antarctica more than ever before, and the ice has been getting thinner in Greenland. Are these indicators that the temperature is rising? Science and technology have led to many inventions and activities that add CO2 to the air. We do not yet fully understand the implications this might have for society and the environment in the future. Australian scientists predict that some of the following changes may occur:

• The melting of much of the polar ice caps would raise sea levels, flooding coasts, cities and some entire island countries. • Expansion of the water in the oceans would also raise sea levels, causing further flooding. • Increases in the numbers of wild storms and cyclones. Cyclones could move further south. • More droughts and heatwaves. • More bushfires. • Less rain and snow. Ski resorts may go out of business. People will need to collect their own water with tanks. • The places animals and plants live in will change. Some may become extinct. • Increased temperatures may cause bacteria to grow faster, causing more disease in humans and other animals. • Some plants may grow faster with higher temperatures. This would be good news for farmers. But less rain may mean that farmers can grow fewer plants and fewer varieties. • Increased heat may cause more humans to suffer from heat stroke and illness. With all these possible changes to the environment it is clear that we must start reducing the amount of greenhouse gases Prac 2 we release into the atmosphere. p. 275

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The atmosphere Are global temperatures increasing?

The ozone hole

Fig 9.5.5

The layer of ozone in the upper stratosphere filters out about 97 per cent of the ultraviolet (UV) radiation from the sunlight falling on Earth. UV radiation is known to cause sunburn, premature aging and, with prolonged exposure, skin cancers, in humans. Without Lucky shrimp ozone we are more likely to Research has suggested develop these conditions. that tiny shrimp-like With our outdoor lifestyle animals called krill naturally make and hot and sunny climate, sunscreen in their own Australians are already exposed shells if they are to high amounts of UV radiation exposed to more UV radiation. Unfortunately, and as a nation we have a higher the rest of us can’t. rate of skin cancer than anywhere else in the world.

Change in average temperature (C)

1.2 1.0 0.8 0.6 0.4 0.2 0 1880

1900

1920

1940 Year

1960

1980

2000

Career profile Greenhouse engineer Engineers are like designers. A greenhouse engineer is really an environmental engineer. Environmental engineers work to design ways to do things better, so that we reduce the impact of humans on the environment. The greenhouse engineer provides advice and services on energy management and greenhouse gas reduction to companies and the government. Environmental engineers are in one of the fastest-growing job areas as we try to find ways to live without harming the Earth. • • • •

• • •

272

Greenhouse engineers can be involved in: measuring greenhouse gas emissions. carrying out environmental audits reviewing facilities to identify where environmental improvements can be made finding ways for companies to reduce greenhouse gas production. A good greenhouse engineer will be able to: work as part of many different teams communicate with people from many different backgrounds apply the scientific method to collect and analyse data

A greenhouse engineer completing air sample testing in the laboratory

• •

Fig 9.5.6

give people clear advice on how to improve what they are doing be passionate about environmental issues.

UNIT

9. 5

1980

Fig 9.5.7

1990

The hole in the ozone layer over Antarctica is getting bigger.

In 1985 it was discovered that the ozone layer over Antarctica was getting thinner: a ‘hole’ had been forming, allowing more UV radiation through to the Earth’s surface. Concern that the thinning of the ozone layer could spread worldwide led to restrictions on the use of chemicals called chlorofluorocarbons. Chlorofluorocarbons (CFCs) are chemicals known to react with ozone, destroying it.

UNIT

9.5

2000

Until recently CFCs were used as the propellants in aerosol cans, in the production of polystyrene and as a coolant in air conditioners and refrigerators. It is thought that these gases slowly rise up into the ozone layer and are reacting with it, causing the ‘hole’. It is now reported that the ozone hole has shrunk a little over the past couple of years. This shows that we can solve environmental problems through scientific research and international cooperation.

[ Questions ]

Checkpoint Layer upon layer 1 Copy the following, and modify any incorrect statements so they become true. a Humans live in the ionosphere. b Commercial aircraft travel in the stratosphere. c Oxygen is the most common gas in the atmosphere. d Meteors burn up in the troposphere. e The ionosphere protects us from X-rays and gamma rays. f The ozone layer is part of the stratosphere. g Weather happens in the troposphere. h Most of the air is in the ionosphere. 2 The atmosphere does not escape into space. Explain why. 3 Identify the layers of the atmosphere that could be considered the: a hottest b coldest c thickest

4 Describe what happens to the air temperature as we go higher in the: a troposphere b stratosphere c mesosphere d ionosphere

What’s in air? 5 Identify the main gases in air and state the percentage of each. 6 Each gas in air has a purpose. Describe a purpose for each gas you listed for Question 5.

The greenhouse effect 7 State whether the greenhouse effect is a natural phenomenon or one caused by humans. 8 Describe why it is important that we have a greenhouse effect on Earth. 9 Identify the cause of the enhanced greenhouse effect. 10 Describe two effects that the enhanced greenhouse effect may have on the Australian environment.

>> 273

The atmosphere

11 Describe two effects that the enhanced greenhouse effect may have on Australian society.

The ozone hole 12 Explain where the ozone layer is and what it does. 13 Identify the chemicals that react with and destroy ozone. 14 Identify where those chemicals were once used.

Think 15 State what these abbreviations stand for. a O2 b O3 c CFC d UV e IR f CO2 g SO2 16 Accurately draw a pie chart showing the percentage of each gas in the atmosphere. 17 Sea levels are expected to rise in the future. a Provide a possible reason for this. b Identify where the water would come from. c Describe the possible effects of this. d Describe three ways in which humans are adding CO2 to the atmosphere. e Propose three ways in which you could reduce the amount of carbon dioxide you personally produce every day. 18 Even though CFCs are generally not used now, they will react with the ozone layer for many more years. Propose a reason why.

Analyse 19 ‘The troposphere is the atmosphere of Earth.’ Explain why: a this statement is wrong b this statement has some truth in it 20 Use Figure 9.5.5 to find the average increase in the average temperature of Earth between: a 1880 and 1990 b 1940 and 2000 21 State which 20-year period showed the greatest increase in Earth’s temperature.

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>>> [ Extension ] Action 1 The enhanced greenhouse effect is a very serious problem. a As a class or in large groups, organise an information display about the enhanced greenhouse effect and global warming. You should include information to teach people about: • what the greenhouse effect is • what the enhanced greenhouse effect is and its causes • the possible effects of the enhanced greenhouse effect on Australia • how people can help reduce the problem through everyday decisions. b Your display should use different ways to communicate such as signs, posters, pictures, video, sound and activities. Make it fun! c Get your display set up in the science area or at science day, open day or even a local shopping centre.

Investigate 2 Record in a diary the day and night temperatures reached over a week and the amount of cloud cover each night. Which days had the greatest difference between day and night temperatures? What was the cloud like on those days? Summarise your findings. 3 a Investigate how sunscreens work. What does the SPF number on a sunscreen indicate? b Examine reasons why Australians are more likely to develop skin cancer, and recommend ways to minimise the risk. Produce a sign/poster for use at the beach to inform sunbathers of the skin cancer risk and solutions.

UNIT

9. 5 Prac 1 Unit 9.5

UNIT

9. 5 [ Practical activities ] An already wet planet

An even wetter planet

Aim To calculate the percentage of water on the Earth’s surface.

Aim To examine what would happen if the sea level rose

Equipment A4 map of the world, graph paper, calculator

Method 1 Trace out the main continents from a map of the world onto graph paper. 2 Count the number of squares covered by the continents. 3 Do not count squares that are less than half-filled. Count squares that are more than half-filled as full squares. 4 Use subtraction to calculate the number covered by water.

Prac 2 Unit 9.5

Method

1 On the map from the previous activity, extend inland all the oceans, seas and bays by one graph-square. 2 Reduce the lands covered in ice by two graph-squares.

Questions 1 Identify which pieces of land have completely disappeared. 2 Describe six problems that would occur in a shrunken world like this. 3 Identify what could cause this to happen in reality.

5 Use a calculator to find the percentage of the Earth that is land by completing this calculation: 100 x Earth squares total squares

6 Calculate the percentage of water on Earth.

Questions 1 Did you count the number of squares covered by lakes and rivers, islands and small land masses? If not, explain why. 2 About 29 per cent of the Earth’s surface is land, while the other 71 per cent is water (97 per cent of that is salt water, 2 per cent is stored as ice in Antarctica and Greenland). Describe any difference between the percentages that you calculated and the percentages given here. 3 State three suggestions as to why your percentages may be different to those given.

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Science focus: Global warming Prescribed focus area: Implications for society and the environment Is global warming a serious cause for concern? Scientists and governments around the world generally agree that human activities are leading to global warming. The main cause of increasing carbon dioxide levels in the atmosphere is the burning of fossil fuels.

Evidence in the ice Scientists collect ice cores from Antarctic ice by drilling down as deep as 4.7 kilometres. The deeper they drill, the older the ice is, as each year new snow falls on top. As snow builds up, tiny air bubbles are trapped in the ice. Scientists can study these trapped gases to work out the amount of carbon dioxide that was in the atmosphere up to nearly 400 000 years ago.

This ice core is being sliced to collect samples of a known age.

Fig SF9.2

On the temperature line, the troughs represent the ice ages when the average temperature was up to six degrees lower than today. The peaks are when warmer periods occurred on Earth.

CO2 and temperature over 420 000 years Predicted level CO2 in 2100

650 600 550

450 400

Fig SF9.1

This piece from an ice core shows tiny bubbles of trapped air from the atmosphere.

The graph in Figure SF9.3 shows carbon dioxide levels in the Earth’s atmosphere for the last 420 000 years. It is normal for the level of carbon dioxide to go up and down, but the amount of carbon dioxide in the atmosphere is now at the highest level ever. Notice that the Earth’s temperature changes in line with changes in the amount of carbon dioxide in the air.

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Temperature (°C)

Current level

350

20

300

10

250 200

0

150

–10 400 000

100 300 000 200 000 100 000 now Predicted Years before present CO2

Fig SF9.3

CO2 (ppm)

500

Temperature

temperature rise by 2100

Carbon dioxide levels over the past 420 000 years. The graph shows a prediction for the year 2100 if humans keep increasing carbon dioxide levels at the current rate.

Evidence of surface temperatures To find out what the temperature on Earth was in the past, scientists use evidence from such sources as tree ring growth or coral cores. These sources, combined with historical records, can only produce results going back about 1000 years. That is because this is the age of the oldest living trees and corals. These measurements also confirm that the Earth's average temperature is rising to its highest level ever.

Evidence from changing weather patterns

rise, possibly flooding many low-lying and coastal communities. This has already created great concern for communities on many small islands. These people are worried that as the oceans rise their whole islands may be lost below the water. Many models on global warming predict that Australia will become drier as temperatures slowly increase. (More possible effects are listed in Unit 9.5.) One thing that is clear is that the Earth is slowly warming, and there is new and stronger evidence that most of the warming observed over the past 50 years has been caused by human activities.

Evidence from coral reefs

The increase in unpredictable weather around the Earth, and the increased frequency of the El Nino weather pattern (alternating droughts and wet periods), has caused many people around the world to consider carefully what the effect of global warming may be. Meteorology is one of the sciences where it is most difficult to make precise predictions. We only have to consider how often weather forecasts are incorrect. It is difficult to make accurate predictions of exactly what will happen as the Earth warms. One prediction is that the polar ice caps on Earth will begin to melt and sea levels will begin to

Over the past decade, there have been increasing records of coral bleaching. Corals have single-celled plants or algae living in their coral tissue and helping them survive. When ocean temperatures increase above 30°C, the algae, essential to the coral’s health, begin to die. This in turn kills the coral. The most recent evidence is of particular concern. Many parts of the Great Barrier Reef are beginning to be bleached. Previously this had only been observed closer to the equator.

Fig SF9.5

There is already worldwide evidence that glaciers are receding and shrinking back up the mountains. Global warming is melting glaciers faster than a few years ago.

This section of the Great Barrier Reef has been bleached and is now dead. The cause was increasing ocean temperatures.

Fig SF9.4

277

Summary of scientific information Atmospheric carbon dioxide changes: • Atmospheric carbon dioxide has increased by 31 per cent since 1750. • About three-quarters of the carbon dioxide emissions produced by humans during the past 20 years has been from the burning of fossil fuels (currently about 6 600 000 000 tonnes per year). A lot more has been caused by land clearing. • As carbon dioxide levels go up, so does the Earth’s temperature. • At present the land and the ocean absorb about half of human carbon dioxide emissions. The rest remains in the atmosphere.

Climate change: • The Earth is experiencing a major change in climate. • Climate change caused by humans will persist for many centuries. • Research is required to collect more information in order to increase our understanding of what may happen in the future. • To stop carbon dioxide levels rising we need to produce less carbon dioxide.

[ Student activities ] 1 A lot of Australia’s electricity and transportation is now produced by the burning of fossil fuels such as coal. , Australians possibly produce more greenhouse gases per person than anyone else in the world. a List the ways that you produce greenhouse gases like carbon dioxide. b List the ways that you, as an individual, can contribute to reducing greenhouse gas emissions. c Pick one of the items on your list and make an effort to do this activity. d Report back to the class about how successful you have been in reducing the amount of carbon dioxide you produce. 2 Many people think that the contribution of an individual will make no difference. But it is definitely true that many little contributions will quickly add together to ultimately make a large contribution. Discuss this topic in small groups. a Explain why some people think that an individual cannot make a difference. b Describe a number of examples to prove that lots of little contributions can add up to be very significant. c Describe why many people, such as friends and family, may find it difficult to make any changes to reduce their use of fossil fuels and electricity use. d List ways that you can help others make small contributions that collectively will reduce the greenhouse emissions created by your school, your home and your community.

278

3 Connect to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, by selecting chapter 9 and clicking on the destinations button. Use the web links available to research the following questions. a Which countries produce the most greenhouse gases? b What is the predicted rise in sea levels over the next 50 years? c Which locations and countries are most at risk from rising sea levels? 4 The world community was concerned enough about global warming to produce the Kyoto protocol. This document was designed to get all countries to agree on ways to produce less carbon dioxide and other greenhouse gases. As of 2004, both Australia and the USA had still not signed the Kyoto protocol. a Research this issue and find out reasons why some say we should sign up while others think we should wait until the evidence is clearer. b Organise a class debate based on the following topic: Australia and the USA should sign the Kyoto protocol as soon as possible.

UNIT

context

9. 6 We often talk about the weather. ‘It’s too hot’, ‘It’s too cold’ or sometimes ‘Today is perfect weather for …’. Sometimes we like the wind, as it helps clothes dry and yachts race, but at other times it messes our hair or blows dust into our eyes. The weather affects our everyday decisions such as what we wear, how we travel, and where we go. Extreme weather causes floods, drought and often destruction. It is therefore important to understand this most important part of our lives.

The Earth’s equator receives a lot more concentrated heat and light energy from the Sun than do the poles, causing the air over the equator to rise and the air over the poles to drop. Convection currents take warm air to the poles and cooler air back to the equator. The atmosphere is also swirled around by the spin of the Earth, creating a series of winds called tradewinds.

light and heat from Sun

Wind As air is heated, it expands and becomes ‘lighter’ or less dense and has lower pressure. Cold air is ‘heavier’, more dense and has a higher pressure than warmer air. Because of this, hot air rises while cold air drops. This process is called convection and happens in our houses, the kitchen oven and in the atmosphere. The Sun’s heat is spread over a smaller area at the equator—this makes the equater hotter.

equator hot air rising air moving in to replace air that has risen

Fig 9.6.1

warm air moving to cooler region

cold air sinking Sunlight is more concentrated at the equator

Sunlight spreads further at the poles

Global movement of air

Fig 9.6.2

In theory, this would cause winds that always blow roughly in the same direction, but winds don’t actually do this. The Sun heats different materials at different rates. Land areas heat up more quickly than lakes, oceans and the seas. Dark colours increase in temperature faster than light colours. This means that bitumen roads, carparks, newly ploughed fields and dark-coloured rocks such as basalt heat faster than sand and marble, fields of crops and shiny metal roofs. Convection currents and winds are created because of differences in temperatures and air pressures in a small area.

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Weather

Fig 9.6.3

Wind patterns over the Earth

Local winds are caused by different heating rates, and differences in air pressure.

Fig 9.6.4

pressure variation

high air pressure low air pressure

surface wind

water, forming clumps of small droplets that we normally call clouds. If the clouds cool further by being pushed upwards or over colder regions, the tiny droplets begin to join to make bigger drops that will fall as rain or, if cold enough, sleet or snow. Tiny specks of high floating dust often start the process. Sometimes it is cold enough for the water vapour to cool just above the land, forming fog. Hail formation is still not fully understood. One explanation is that the Severe thunderstorms supercooled raindrops freeze These usually develop in the on the surface of dust particles late afternoon when the atmosphere is moist and or snow. These small unstable. High cumulonimbus hailstones are blown up and clouds rapidly develop with down inside the cloud by the lightning, thunder, severe wind gusts, heavy rain and large storm’s wind. They gradually hail. Many thunderstorms are gather more water and shortlived (about one hour), increase in size until they and limited in size. They can become too heavy and fall travel large distances and cause significant damage. The to the ground. Another 1999 Sydney thunderstorm explanation is that they grow was unusual in that it lasted in size as they fall through over five hours, with hailstones measuring up to the storm cloud. 9 cm. The rain, hail and wind All this water evaporating affected 22 000 properties, and falling back as rain forms with $2 billion in insurance part of the water cycle, as losses. shown in Figure 9.6.5. Clouds are cooled water vapour. This is called condensation. If the drops are heavy enough, they fall as rain. This flow of water from sea to clouds to rain, then run-off from land to sea, is called the ‘water cycle’.

Winds move from areas of high pressure to fill the ‘gap’ created in areas of low pressure.

Looks like rain! Water is constantly evaporating from anything wet on Earth, Prac 1 p. 284 whether it is a lake, the ocean, or the washing on a clothesline. More water evaporates from the oceans and seas than anywhere else. This warm water vapour rises, cooling as it gets into higher and colder levels of the atmosphere. When cold enough, it condenses back into liquid

280

Fig 9.6.5

clouds form

water droplets fall as rain water evaporates

rain water run-off rain water run-off

sea or lake

Too much movement … storms

a Cumulus clouds do not produce rain.

b Altocumulus clouds produce light showers.

c Stratocumulus clouds produce drizzle.

d Cirrus clouds consist of ice crystals, and do not produce rain.

e Stratus clouds produce drizzle or fine rain. They may form fog at low levels.

f Cumulonimbus clouds produce thunderstorms with lightning.

g Nimbostratus clouds produce heavy rain or snow.

h Cirrocumulus clouds do not produce rain.

Fig 9.6.6

In the southern hemisphere, winds move in a clockwise direction around a low on a weather map, and anticlockwise around a high. A cyclone (known as a hurricane in the USA and a typhoon in Asia) begins as an intense low over a stretch of ocean, usually in the tropics. The warm humid air begins to spiral clockwise and upwards, cooling and condensing as it goes. Energy is released and the air is warmed again, forcing it to go even higher, reducing the air pressure at ground level even more. Air is sucked in from the seas around, bringing high-speed winds and torrential rain. The cyclone usually keeps going until it passes over land and loses its supply of water and its energy.

UNIT

9. 6 It’s raining fish! There have been over 20 reports of fish raining down over Australia in the past 50 years. A man on the northern coast of NSW woke up to find fish all over the roof of his house. In 1989 sardines showered down on sunny Ipswich in Queensland. Three fish storms occurred in the same month in Killarney, 320 km inland from the Northern Territory coast. A cyclone can suck up water from a lake or the ocean, taking fish with it. The fish are carried into the thunderstorm clouds and fall with rain. If the storm goes high enough into the atmosphere the fish can be carried for hundreds of kilometres in jet stream winds. They can rain down from clear skies hundreds of kilometres from the ocean or storms. Many other animals have been reported as rain, including snails, eels, mussels, frogs, spiders and even snakes.

Clouds

Worksheet 9.4 Cloud types

A satellite image of a low pressure weather system off Australia’s southern coast. Note that the winds spiral clockwise and move towards low pressure.

Fig 9.6.7

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Weather

dry air sinking

spiralling moist air cooled air sinking

eye

rain

warm moist air sucked in

Tropical cyclones cause massive amounts of air to shift.

Fig 9.6.8

Career profile Meteorologist Meteorologists forecast the weather and study the atmosphere to improve our understanding of the Earth’s climate. Meteorologists can have a major effect on both society and the environment. Their weather predictions affect our society every day, especially when the forecast is inaccurate. Their advance warnings for dangerous weather can save both lives and property.

•

A meteorologist can be involved in: using different scientific instruments to forecast the weather examining satellite images of clouds for dangerous weather preparing special reports for shipping, agriculture, fishing and flying issuing warnings of cyclones, storms, floods, frosts, fire dangers and strong winds reporting air pollution.

• • • •

A good meteorologist will be able to: record and analyse many different types of data be part of a team use different instruments to gather data in the field write accurate reports.

• • • •

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Meteorologists releasing a weather balloon to measure temperature and humidity in the atmosphere

Fig 9.6.9

UNIT

9. 6

UNIT

9.6 [ Questions ]

Checkpoint Wind 1 Copy the following and modify any incorrect statements so they become true. a Hot air rises and cold air drops. b The equator receives more concentrated heat energy from the Sun than the poles do. c Hot air circulates away from the poles to the equator. d Tradewinds are local winds. e All rocks heat up at the same rate.

Looks like rain!

Analyse 17 Predict the direction of the winds in the areas shown in Figure 9.6.10. Fig 9.6.10 forest

bitumen

road

2 Identify these processes. a H2O (l) → H2O (g) b H2O (g) → H2O (l) 3 Explain what is needed to cause a cloud to rain. 4 Identify the types of clouds most likely to cause rain. 5 In your own words, describe what the water cycle is.

land

sea

Too much movement … storms 6 List the other names used for cyclones. 7 Describe what causes a cyclone to begin. 8 Identify what causes a cyclone to lose strength. white sand

Think

black rocks

9 Explain why it is unwise to eat snow. 10 Explain why the poles would be even colder if there were no convection currents. 11 Predict whether the temperatures at the equator would be higher or lower if there were no convection currents. 12 Gliders often increase their height by riding ‘thermals’ (rising hot air). Identify where these might be found. 13 Draw a simplified diagram to demonstrate the water cycle. 14 Plants are also involved in the water cycle. Describe how you think they fit in.

18 Gather weather maps from the newspaper for one week. Then use each map to do the following: a Draw arrows on the maps to indicate the directions you would expect the winds to blow. b Shade areas where it would be warmer in red, and cooler in blue. c Draw water drops or snow flakes where you would expect rain or snow. d Write a summary to describe Australia’s weather over the week.

15 The water in your body could once have been in the body of a great scientist. Explain how this could be possible. 16 In your own words, summarise the role of a meteorologist.

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Weather

[ Extension ] Investigate 1 Keep a diary of the types of clouds you see over the next week and any rainfall (none, rain, drizzle, spitting) that occurs. 2 Investigate how tornadoes form and why they are rare in Australia but common in the USA. Also find out how storm chasers in the USA collect information about tornadoes.

4 Set up a weather station in your school grounds and monitor the weather.

Surf 5 Look at satellite photos of the weather and learn more about forecasting by connecting to the Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 9, and clicking on the destinations button.

Action 3 Construct a model of the water cycle using a fish tank with a lid on. Set up the inside of the tank to look like a part of the surface of the Earth. Attach labels to the outside of the glass to explain what is occurring in each part of the tank.

UNIT

9. 6

DYO

[ Practical activity ] Making clouds Aim To determine what conditions are needed to

Prac 1 Unit 9.6

make clouds

Equipment 400 mL beaker, ice cubes, evaporating dish, Bunsen burner, bench mat, tripod, gauze mat and matches, safety glasses

Method 1 Heat about 100 mL of water in the beaker until boiling. 2 Turn off the gas and cover the beaker with an evaporating dish. 3 Observe and note in your results what happens. 4 Repeat the experiment but this time place ice cubes in the evaporating dish as shown in Figure 9.6.11. 5 Write down your observations in your results.

ice cubes

Questions evaporating dish 400 mL beaker

1 Explain what water vapour is. 2 Describe what happens to water vapour as it cools. 3 Explain how cooling water vapour could cause a cloud.

Fig 9.6.11

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Water vapour condenses to form clouds.

Chapter review [ Summary questions ]

[ Thinking questions ]

3 1 True or false? a The radius of the Earth is approximately 12 800 km. b The thickest layer of the Earth is the mantle. c Sedimentary rock is a type of mineral. d Rocks can contain a number of different minerals. 4 e The mantle is where most volcanic and earthquake activity occurs. f The crust is thickest under the continents. g The moving around of pieces of rock by wind and 5 water is called weathering. 6 h The layer of the atmosphere that humans and animals live in is called the stratosphere. i The magnetic field of the Earth comes from movements in the outer core. 7 j Winds move in a clockwise direction around a low. k Condensation is the name given when water turns 8 from liquid to vapour. l Hot air is more dense than cold air. m Water heats up more quickly than rock. n The Sun heats up the atmosphere. o Australians add 70 tonnes of carbon dioxide to the atmosphere each year. 9 p At night the Earth releases heat back into the atmosphere. 10 q Greenhouse gases trap heat in the atmosphere. Rock type r More CO2 in the atmosphere traps more heat. Sedimentary s Clouds help trap heat in the atmosphere Metamorphic on cold nights. Igneous 2 Draw simplified diagrams to demonstrate any three of the following: a the rock cycle 11 b the water cycle c the Earth’s structure 12 d the greenhouse effect 13 e acid rain

Use a diagram to explain why: a the Mediterranean Sea is being slowly squeezed shut b the Atlantic ocean is getting wider c the Himalayan mountains are getting higher Identify in which layer of the atmosphere is: a the ozone layer b the layer we live in Describe where the ‘ozone hole’ is located. Describe the effects in the future if: a the ozone hole continues to increase b carbon dioxide concentrations increase further c acids are continually released into the air List eight types of cloud in order from those most likely to give heavy rain to those that will not bring any rain. Compare the following items: a rock and mineral b crystal and mineral c pigment and streak d rock and ore Identify the element that may be extracted from chalcopyrite. Match a rock type to a description.

Description Formed from molten material Made from broken down particles compressed into layers Made from other rocks changed by heat and/or pressure

Identify two uses for each major type of rock. Describe two uses that Aboriginals had for rocks. a Explain the term ‘ochre’. b Describe how ochres were prepared and used by the Aboriginals.

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>>> [ Interpreting questions ] 14 Copy and complete the following table to summarise the science careers covered in this chapter.

Job title

Main tasks

Skills required

Geologist Palaeontologist Environmental scientist Greenhouse engineer Meteorologist

15 Identify two other science careers not included in the table in Question 14, but mentioned in this chapter. 16 Draw a diagram to demonstrate the wind direction around a low-pressure system. 17 Make a sketch to demonstrate the air movement around a cyclone. 18 Place in order from hardest to softest: calcite, quartz, corundum, topaz. 19 On Mohs’ scale a particular mineral has a hardness of 6.5. Identify a mineral it would: a be able to scratch b not be able to scratch 20 Classify as sedimentary, igneous or metamorphic: a shale b sandstone c granite d limestone e conglomerate f gneiss g basalt

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21 List these layers of the Earth and atmosphere in the correct order starting from the centre of the Earth: outer core, stratosphere, troposphere, mantle, inner core, ionosphere, mesosphere, troposphere, crust. 22 From the list in Question 21, identify which layer: a is the hottest b is about 20–25°C on average c is made of liquid rock d is where the jet stream winds occur e contains most of the air f is made mostly of iron and nickel Worksheet 9.5 Our planet Earth wordfind Worksheet 9.6 Sci-words

bacteria, 94 beam balance, 19–20 bearings, 192 bimetallic strip, 49 binominal name, 157 biology, 6 birds, 163 boiling (liquid), 42 Brahe, Tycho, 217 breezes, wind and sea, 121–122 Brown, Robert, 37, 97 Brownian motion, 37, 46–47 Bunsen, Robert, 27 Bunsen burner, 27–28 buoyancy, 204 carnivorous plants, 149 cathode ray oscilloscope (CRO), 140–141 cells, 87–106, 151 animal, 95 cloning, 104, 108–110 human, 99, 103–106 parts of, 95 plant, 96, 100 stem, 108–111 theory, 94 Celsius, Anders, 118 centrifuging, 70 changes of state, 41–44 characteristics (of life), 148 chemistry, 6 chlorine, 79 chlorofluorocarbons, 273 chlorophyll, 96 chloroplast, 96 chordates, 161, 174 chromatography, 61, 75, 78 classification, 155–158 animals, 161–168, 174 indigenous, 167–168 keys, 176–178 plants, 171–174 climate change, 276–278 coal, 258 clouds, 280–281 cnidarians, 165 cold blooded, 149 colloid, 64 compass, 209 compression in liquids, 36 in sound waves, 137 concentration, 63 conclusion, 6 condensation, 42, 280

conduction, 118–119 contraction, 48, 49 convection, 120–122 Copernicus, Nicolas, 216, 229 crustaceans, 167 crystallisation, 74 cyclone, 281 day and night, 235 decanting, 69 decibel scale, density, 54–56, 204 diffuse reflection, 130 diffusion, 37, 40 dilute, 63 dissolving, 37 distillation, 74–75 domain (magnetic), 209 drag, 201 dyke, 256 Earth, 219–220 crust, 247 mantle, 247 core, 247–248 earthquakes, 248 echoes, 139 echolocation, 139–140 eclipse lunar, 241–242 solar, 233 ecology, 6 ectothermic, 149 elastic, 183 electrolytes, 79 electromagnetic waves, 122 electrostatic separation, 71 emulsion, 64 endothermic, 149 energy, 113–115 conservation, 115 heat, 118–123 kinetic, 113 light, 129–132 potential, 113 production, sound, 137–142 source, 115 transformation, 114 enhanced greenhouse effect, 271 environmental scientist, 266 equinox, 237 equipment, 12, 28 drawing of, 12–13 erosion, 260, 264–265 and people, 265–266 errors parallax, 19 reading, 18 zero, 19 evaporation, 74, 280 excretion, 150 exoskeleton, 166 expansion, 48–51 experiment, 6, 46 family, 156 fertile, 157 filtration, 69–70 fish, 163–164 floating and sinking, 55–56 flocculation, 79 fluoride, 79 foam, 64 forces balanced/unbalanced, 188–189, 201–202 contact, 183–193 drawing, 184

frictional, 188, 191–193, 201–202 gravitational, 188, 196–197, 201–202 in water, 204–205 magnetic, 208–210 measuring, 184 non contact, 196–197, 208–210 freezing, 42 friction, 188, 191–193, 201–202 reducing, 192 using, 192–193, 202 froth flotation, 71 fungi, 172–173

INDEX

absorption of heat, 123 of liquid, 75 of sound, 140 acceleration, 183 acid rain, 264, 265 activated sludge process, 82 aeration tank, 82 amphibians, 162 animals, classification, 161–168 arachnids, 166 Aristarchus, 216 Aristotle, 216 arthropods, 166 asteroids, 221 astronomical unit, 217, 231 astronomy, 6, 228–230 indigenous, 228 atmosphere (Earth’s), 269–273 aurorae, 233 autotrophs, 149

Galileo, 217, 222, 230 Galle, Johann, 224 gases, 37, 42–43, expansion of, 50–51 gel, 65 genus, 156 geology, 6 geologist, 261 global warming, 271, 276 evidence of, 276–277 gravity, 188, 196–197, 201–202 separation, 70 Great Barrier Reef, 277 greenhouse effect, 270–271 enhanced, 271 growth, 151 heat, 118 energy, 118–123 hemispheres, 237 Herschel, William, 223 heterotrophs, 149 Hooke, Robert, 87, 93 humans, impact of, 265–266 hurricane, 281 hypothesis, 24 igneous rocks, 256–257 extrusive, 256 intrusive, 256 uses of, 257 images (reflections), 131 imperial units, 18 inference, 9 insects, 166 insoluble, 63 insulation, 119–120 invertebrates, 165–167 ionosphere, 269, 270 joule, 113 Joule, James, 113 Jupiter, 221–222 Kepler, Johannes, key, 158 branching, 176 circular, 177–178 dichotomous, 158 tabular, 158, 177 kingdom, 156 lateral inversion, 131 lava, 256 law of reflection, 130–131 light, 129–132 Linnaeus, Carolus, 156 lime, 79 liquids, 35–36, 41–42, 49–50 expansion of, 49–50 luminous (and non-luminous), 129 lunar eclipse, 241–242 landscape, 240

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Index Magellan Venus orbiter, 218 magma, 256 magnetic fields, 209–210 forces, 208–210 separation, 70 magnets, 208–210 electromagnet, 209 mammals, 164 Mariner (space probe), 218, 219 Mars, 220–221 marsupials, 164 mass, 196, 197 matter, 35 measurement, units of, 18–19, 118 measuring, 18–20 equipment, 20–21 forces, 20–21, 184, 196 mass, 20–21, 196, 197 melting, 41 meniscus, 19 Mercury (planet), 217 mesosphere, 269 Messenger (space probe), 218 metamorphic rocks, 259 meteorologist, 282 metric system, 18 microscope, 87–91 compound, 87 electron, 89–91 simple, 87 sketching images, 89 stereo, 87–88 using a, 88–89 mineralogist, 251 minerals, 251 indigenous uses, 252 properties, 252–253 mirror plane, 131 mist, 65 mistake, 18–19 mitrochondria, 95 mixtures, 62–65 separation, 68–71, 74–75 molluscs, 167 monera, 173 monotremes, 164 Moon, 239–242 landscape, 240 phases, 240–241 statistics, 239 multicellular, 99 music, 141 Neptune, 224 Newton, Sir Isaac, 184 newtons, 196 normal, 130 nuclear fusion, 231 observations qualitative, 9 quantitative, 9 order, 156 ores, 253–254 organs, 103 organisms multicellular, 99–100 unicellular, 100–101 ozone, 269–270, 273 hole, 272–273 layer, 269, 270 paleontologist, 259 parallax error, 19

288

particle model, 35–37 Pathfinder mission to Mars, 221 pebble bed filter, 82 petrologist, 251 photosynthesis, 96, 149 phylum, 156 physics, 6 planets, 216–225 plants, classification, 171–175 plate tectonics, 249 Pluto, 224–225 pollution, 264, 265, 266 predictions, 9 pressure (and weather), 279–281 protists, 173 Ptolemy, 216, 229 Pythagoras, 216 qualitative observations, 9 quantitative observations, 9 radiation, 122–123 rain, 280 ray tracing, 131 reading error, 18 reflection heat, 123 light, 130 refrigerators, 42 regular reflection, 130 reports, 15–16 reproduction (sexual, asexual), 151 reptiles, 162 resonance, 141 reverberation, 140 rock cycle, 260 rocks igneous, 256–257 metamorphic, 259 sedimentary, 257–258 safety in the laboratory, 3 saturated solution, 63 Saturn, 222–223 Schleiden Matthias, 94, 98 Schwann, Theodor, 94, 96 scientific drawings, 12–13 equipment, 12–13, 27–28 models, 35–37, 46–47 reports, 15 seasons, 236–237 sediment, 63, 257, 264 sedimentary rocks, 257–259 separation of mixtures, 69–75 septic tank, 81 settling tank, 82 sewage, 81–82 sewerage, 81 shadows, 129–130 sieving, 69 sky diving, 202 smells, 37–38 smoke, 65 soda ash, 79 solar atmosphere, 232 eclipse, 233 energy, 231–233 flares, 232 prominences, 233 statistics, 232 wind, 233 solar system, 216–225 geocentric, 216, 229 heliocentric, 216, 229 history, 216–217, 228–230

solidification, 42 solids, 35–36, 41–43, expansion of, 48–49 sols, 64 solstice, 237 solubility, 63 solute, 62 solutions, 62–63 solvent, 62 sonic boom, 139 sound, 137–142 graphs, 140–141 levels, 141–142 speed, 139 transmission, 137 waves, 137–138 space, Earth’s movement in, 235–237 species, naming, 157 specific gravity, 56 states of matter, 35, 41–44, 46–47 stimulus, 150 storms, 280, 281–282 stratosphere, 269 sublimation, 43 Sun, 231–233 prominences, 233 sunspots, 232 surface tension, 204–205 suspensions, 63 taxonomy, 155 temperature, 118 thermos flasks, 123 thermosphere, 269 thrust, 201 tides, 241 tissue, 103 Tombaugh, Clyde, 224 tradewinds, 279 troposphere, 269 typhoon, 281 ultrasound, 140 unicellular organisms, 100–101 Uranus, 223 vacuoles, 95 van Leeuwenhoek, Antoni 91 vaporisation, 42 variables, 24–25 Venus, 218–219 vertebrates, 161–164 Viking (space probes), 220 virtual image, 131, 132 volcanoes, 248 volume, 55 Voyager (space probe), 221, 222, 223, 224 warm blooded, 149 water cycle, 280 expansion of, 49–50 supply, 79–82 waves electromagnetic, 122 sound, 137–138 longitudinal, transverse, 138 weather, 276–278, 279–282 weathering, 260, 264–266 biological, 264 chemical, 264–265 physical, 264 weight, 188, 196, 197, 201–202 wind, 121–122, 269, 279 worms, 167 year, 236