3195765 Machines Mteducare Icse 10th Notes.doc

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Index I. Do we know? II. Points of Content A. Machines i. Definition ii. Functions and Uses iii. Technical terms iv. Principle v. Relation between Efficiency, M.A. And V.R. B. Levers i. Definition ii. Principle iii. Kinds of Levers (1) Class I Levers (2) Class II Levers (3) Class III Levers (4) Levers in human body iv. Numericals C. Inclined plane i. Definition ii. Mechanical Advantage D. Pulleys i. Types ii. Single fixed pulley (1) Mechanical advantage (2) Velocity ratio (3) Efficiency iii. Single movable pulley (1) Mechanical advantage (2) Velocity ratio (3) Efficiency iv. Combination of block and tackle pulleys v. M.A.,V.R., Efficiency of combination of block and tackle pulleys   PAGE \*

134 vi. Numericals E. Mindmaps/diagrams/tables/charts III. Objective Questions

1.

Machines as force multipliers;

2.

load, effort, mechanical advantage, velocity ratio and efficiency;

3.

Simple treatment of levers, inclined plane and pulley systems showing the

utility of each type of machine.

1. Machines as force multipliers; load, effort, mechanical advantage, velocity ratio and efficiency; simple treatment of levers, inclined plane and pulley systems showing the utility of each type of machine. a. Functions and uses of simple machines. b.

Technical terms: effort E, load L, mechanical advantage

ratio c. d.

, input (Wi), output (Wo),efficiency( ), Relation between  and MA,VR ;for all practical machines  Load arm and

hence the mechanical advantage in this case must always be greater than 1.__________________________________________________________________________ ___________________________________________________________________________

Q.4.

Draw diagrams to illustrate the positions of fulcrum, load and effort, in each of the

following: i) A seesaw ii) A common balance iii) A nut cracker iv) Forceps.

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(1) Class I Levers Features of Class One Lever Fulcrum is in between load and effort By adjusting the position of fulcrum towards load the mechanical advantage of the class one lever can be increased Examples: pair of scissors, See – Saw, Crowbar ,Water pump, Pliers, Claw hammer

Q.1.

Give two examples of class I lever.

Ans.

_______________________________________________________________

_____________________________________________________________________ _____________________________________________________________________ Q.2.

Class I lever is that in which: i) fulcrum is between the load and effort ii) load is between the fulcrum and effort iii) effort is between the load and fulcrum iv) Fulcrum, load and effort are at one point.

Ans. Q.3.

Fulcrum is between the load and effort

Give one example each of a Class I lever where mechanical advantage is (a) more

than one, and (b) less than one. Ans.

_______________________________________________________________

_____________________________________________________________________ ____________________________________________________________________ Q.4.

Give an example of a class I lever which has mechanical advantage equal to 1. How

can the mechanical advantage of this lever be made greater than one?   PAGE \*

134 Ans.

_______________________________________________________________

_____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ Q.1.

A pair of scissor and a pair of pliers both belong to the same class of levers. Name the

class of lever. Which one has the M.A. less than 1? Ans. Q.4.

Class I, Scissors

Explain why scissors for cutting cloth may have blades longer than the handles, but

shears for cutting metals have short blades and long handles. Ans.

Shears, used for cutting the thin metal sheets, have much longer handles as

compared to its blades. Hence, In a shear, the effort arm is longer than the load arm, the mechanical advantage and the velocity ratio of the lever are greater than 1. Such a lever serves as a force multiplier, i.e., it enables us to overcome a large resistive force (load) by a small effort. However, In a scissor , effort arm is shorter than the load arm, its mechanical advantage and velocity ratio both are less than .Such levers are used to obtain gain in speed because the velocity ratio less than 1 implies
i.e., the displacement of load is more as compared to the displacement of effort. The scissors is used to work on loads (cloth, paper, etc) with high speed. Q.1.

Draw a labelled diagram of a Class I lever. Give one example of such a lever.

Ans.

(2) Class II Levers Characteristics of Class Two Lever Load is in between effort and fulcrum Mechanical advantage is always greater than one, because effort arm is always greater than load arm. Examples: Nut cracker, Wheelbarrow, Bottle opener, Lemon squeezer

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Q.1.

Give two examples of class II lever.

Ans.

_______________________________________________________________

_____________________________________________________________________ ____________________________________________________________________ Q.2.

Explain why the M.A. of a Class II type of lever is always more than one.

Ans.

_______________________________________________________________

_____________________________________________________________________ _____________________________________________________________________ ____________________________________________________________________ Q.3.

Draw a labelled diagram of a Class II lever. Give one example of such a lever.

Ans.

(3) Class III Levers Characteristics of Class Three Lever Effort is between fulcrum and load Mechanical advantage is always less than one because effort arm is always smaller than load   PAGE \*

134 arm Examples: Fire tongs, Forceps, Forearm ,Fishing rod

Q.1.

Give two examples of class III lever.

Ans.

_______________________________________________________________

_____________________________________________________________________ ____________________________________________________________________ Q.2.

Explain why the M.A. of the class III type of lever is always less than one.

Ans.

By principle of Machines, Effort × Effort ARM = load × Load ARM

In class-III levers effort E is in between the fulcrum F and Load L In this case, Effort ARM < Load ARM,