Physics SBA's 1-8

Physics SBA #1: Estimating Area Aim: To estimate the area of an irregular lamina by counting squares Apparatus: irregular lamina; graph paper; pencil Diagram:

Method: 1. 2. 3. 4.

Obtain an irregular lamina Place it over a sheet of graph paper Trace the outline of the lamina on the graph page Count the number of whole and partial squares within the outline of the lamina – record these numbers 5. Estimate the area of the lamina Results: Number of whole squares = Number of ½ squares = Calculations: Area of lamina covered by whole squares = # of squares × area of one square Area of lamina covered by ½ squares = #number of ½ squares ×area of ½ square Total area = area covered by whole squares + area of ½ squares

Questions: 1. How could the value of area be made more accurate? 2. What are the units of area in cm2?

Physics SBA # 3: Acceleration due to gravity Aim: To determine a value for acceleration due to gravity [g] using the simple pendulum Diagram:

Method 1. Attach string to the pendulum bob to from a pendulum [measure and record the length of pendulum – this starting length should be the longest ] 2. Measure and record the time [period] for 20 oscillations [1 oscillation is the movement of the pendulum from one extreme to the next and back] 3.

Repeat step 2 two more times recording all results.

4. Shorten the pendulum [the length by which the pendulum is shortened must be chosen carefully to allow repeated shortening by the same amount] and record the new length. Repeat steps 1 –3 5.

Repeat step 4 three more times recording all results

Results Length [cm]

Time 1

A B C D E

Calculations For length A average time for 20 oscillations = = TA

Time 2

Time 3

Time for 1oscillation = = D [Time for 1 oscillation] squared = D2 REPEAT FOR ALL LENGTHS!!!

Graph Plot a graph of D2 [y] against length [x].

Questions & further calculations Q1 – What is the gradient of the graph? – include units! Q2 – Calculate the value for acceleration due to gravity using the formula ; where m is the gradient of the graph. Q3 – What can be done to make the value of g more accurate?

Physics SBA #4: Centre of Gravity Aim: To find the centre gravity of an irregular lamina Diagram:

Method:

1. Obtain [cut out!!!] an irregular shape and make a plumb line [a string and a pendulum bob] 2. Punch 4 holes in the shape [lamina] – ensure the holes are not too close to the edge of the lamina – label them A, B, C, D. 3. Place a pin or nail between two pieces of cardboard. Secure firmly between the clamp. 4. Place lamina on pin/nail [use hole A]. Suspend plumb line from pin/nail and mark the points on the edges of the lamina where the plumb line crosses the edges of the lamina. 5. Repeat step 4 for remaining holes. 6. Attempt to balance lamina from point of intersection of the four lines. Results 1. A traced outline of the lamina and the location of the lines on it. 2. Did the lamina balance at the intersection of the lines?

Questions 1. How do the lines drawn help to find the lamina’s centre of gravity? 2. Why does the lamina’s centre of gravity lie below the point of suspension?

SBA #5 [PD #1] Hypothesis: The height of rebound of a rubber ball decreases with the addition of paper towels. Aim: To determine if the height of rebound of a rubber ball depends on the number of paper towels it lands on Apparatus: metre rule: rubber ball; paper towels Diagram

Variables: There are usually only two variables in any experiment. The independent variable is the one you change or control while the dependent variable responds to changes in the independent variable.

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Independent: Dependent

Method: the method is usually written in present tense in P&D’s since the purpose of a P&D lab is to provide instruction for someone else to follow [in other words you haven’t done it yet so you can’t write the lab like you did it!] 1. Securely place meter rule vertically against a wall 2. Mark off a suitable release height [HO] , [the ball must be allowed to FALL vertically and REBOUND on nearly the same straight line] 3. With no paper towels at the base of the meter ruler, release the rubber ball from the marked height [the ball must be completely above the marked line with its bottom edge just touching the line] 4. Observe and record the rebound height of the ball [HR], [this should be done from in front of the ruler and eye level]. Repeat twice for this number of paper towels. Record all data. 5. Place a single paper towel at the base of the ruler and release it from marked height. 6. Observe and record the rebound height of the ball. Repeat steps 4 and 5 twice for that number of paper towels, recording all data 7. Continue adding paper towels and repeat step 6 until there are 8 paper towels. 8. Calculate average rebound height [Hr] for each number of paper towels 9. Plot a graph of Rebound Height [y axis] against Number of paper towels [x axis] Results:

# of paper towels

Att. 1 Rebound Height

Att 2 Rebound Height

Att 3 Rebound Height

0 1

Calculations Average height, Hr [for X paper towels] = From calculated data, generate the table below.

# of paper towels

Average Rebound Height, HR/cm

Using the data in the table plot a graph of [average] rebound height against number of paper towels.

Interpretation of results: The gradient of the graph, which must be calculated, will indicate the nature of the relationship between the number of paper towels and the rebound height. If the gradient is positive then as the number of paper towels increases, the height of rebound also increases and vice versa which means the number of paper towels is proportional to the rebound height. Precautions/source of error Question: How does the addition of paper towels reduce the height to which the rubber ball rebounds?

Physics SBA 6: Determining the Spring Constant

Aim: To determine the value of the spring constant of a spring Apparatus: 2 retort stands; spring; mass holder; 20g masses; ½ metre rule Diagram:

Method: 1. Measure and record the original [unstretched] length of the spring. 2. Setup apparatus as shown in diagram [use a pointer – a straight wire – to indicate the bottom of the spring along the ½ metre rule. 3. Attach the mass holder to the spring – measure and record extension of the spring along with the mass of the mass holder. 4. Gradually add 20g masses [one at a time] to the mass holder. After adding each mass measure and record the extension obtained. 5. Remove mass holder and repeat steps 3 and 4 two more times.

Results Length of unstretched spring = ________ cm Mass/g

50 70 90 110 130 150 Calculations:

Attempt 1: Extension/cm

Attempt 2: Extension/cm

Attempt 3: Extension/cm

1. Mass to Weight using w =mg [50g/1000] × 10 = 0.5N [repeat for all other masses] 2. Calculation of extension Average extension = [Attempt 1 + Attempt 2 + Attempt 3]/3

Graph Plot graph of force [Newtons; y-axis] vs extension [cm; x-axis]

Gradient Calculate the gradient of the graph.

Questions: 1. What quantity does the gradient of this graph give us? 2. What is the value of the gradient in N/m or Nm-1

Physics SBA [P&D #2] Hypothesis: In a pendulum made from paper clips if the number of paper clips is increased the period of the pendulum increases also. Aim: To determine the relationship between the number of paper clips [in a pendulum made from paper clips] and the period of the pendulum. Apparatus: pin; wooden blocks; paper clips: pendulum bob; ruler; stopwatch; paper clips Diagram:

Method: 1. 2. 3. 4. 5.

Hook eight paper clips together to form a ‘string’ of paper clips Attach the pendulum bob to the ‘string’ of paper clips Set the paper clip pendulum swinging timing 10 oscillations with the stopwatch Repeat step 4 twice for that number of paper clips, recording all results Remove one paper clip and repeat steps 3 and 4 until three paper clips are left.

Results:

# of paper clips

Try 1 [time for 10 oscillations]

Try 2 [time for 10 oscillations]

Try 3 [time for 10 oscillations]

8 7 6 5 4 3

Treatment of results: 1. 2. 3. 4.

Calculate the average time for 10 oscillations for each length of the pendulum Calculate the time for 1 oscillation for each length of the pendulum Plot a graph of period [y-axis] vs # of paper clips [x-axis] Calculate gradient of graph

NB: give sample calculations for steps 1 & 2 of treatment of results; sketch and label axes for graph to be plotted; give sample calculation for gradient. If the gradient/slope of the graph is positive as the number of paper clips increases so does the period of the pendulum. If the gradient/slope is negative, as the number of paper clips decreases so does the period of the pendulum.

Precautions/sources of error – list please

Physics SBA # 8: Finding mass using the principle of moments

Aim: To find the mass of a rubber stopper using the principle of moments Apparatus: ½ metre rule; 5, 10 & 20g masses; rubber stopper; pivot [a triangular prism could be used] Diagram:

Procedure: 1. Find the metre rule’s centre of gravity by balancing it on a finger tip [mark and record this location] 2. Balance ruler on pivot [ a triangular prism may be used] 3. Place rubber stopper on the metre rule on one side of the pivot, then attempt to balance the ruler by placing masses [gently, gradually and one at a time] on the other side of the pivot [as in the diagram] 4. Measure and record the distance from pivot to both stopper and masses 5. Repeat steps 3 & 4 for four[4] new pivot-to-stopper distances Results: d1 = distance from pivot to stopper d2 = distance from pivot to masses

Mass of Masses

d1

d2

Calculations: 1. Convert mass to weight for each pair of distances. 2. Use the equation,

to calculate the weight of the stopper for each pair of distances. 3. Then calculate the average weight of the stopper. 4. Using the weight of the stopper calculate the mass of the stopper.