Simple Machines
EXERCISES
BE PROMPT
A. Fill in the blanks.
1. Work is said to be done when a force moves a body in its own direction.
2. If a force causes zero displacement, then work done is zero.
3. Complex machines are made of a combination of two or more simple machines.
4. A screw jack acts as a force multiplier.
5. In a class III lever, the effort is between the load and the fulcrum.
6. A screw is commonly used for holding things together and lifting materials.
7. The sharper the wedge, the easier it is to pierce the objects.
B. State whether the following statements are true (T) or false (F). Correct the false statements.
1. A simple machine makes work easier by providing energy on its own. [F]
= A simple machine makes work easier by amplifying the input force.
2. Class II lever works like a force multiplier. [T]
3. The smaller the lead of a screw, the higher is the mechanical advantage. [T]
4. A movable pulley reduces the effort used to pull the load. [T]
5. The wheel and axle must move alternately to form a simple machine. [F]
= The wheel and axle must move together to form a simple machine.
6. The efficiency of every machine used by us is always equal to 100%. [F]
= The efficiency of every machine used by is always less than 100%.
C. Choose the correct option.
1. Which of these statements about lever is not true?
a) It is used to lift heavy weights with minimum amount of force. [ ]
b) It amplifies the input force. [ ]
c) It is a rigid bar or rod pivoted on a fixed support. [ ]
d) It is used as a speed multiplier. [✓]
2. If the load is between the fulcrum and the effort, the lever belongs to ____________ .
a) class I. [ ]
b) class II. [✓]
c. class III. [ ]
d) both (a) and (b). [ ]
3. The mechanical advantage of an inclined plane is _________ .
a) always equal to 1. [ ]
b) always less than 1. [ ]
c) always greater than 1. [✓]
d) mostly greater than 1. [ ]
4. Class III lever is used as ____________ .
a) distance multiplier. [ ]
b) force multiplier. [ ]
c) speed multiplier. [✓]
d) energy multiplier. [ ]
5. Which of these is not an example of a fixed pulley?
a) Well. [ ]
b) Flagpole. [ ]
c) Crane. [✓]
d) None of these. [ ]
6. The linear distance covered by the screw in one complete turn is called its __________ .
a) pitch. [ ]
b) fulcrum. [ ]
c) axle. [ ]
d) lead. [✓]
D. Match the columns.
=
|
Column A |
Column B |
|---|---|
|
1. Class I lever |
(a) Bolts. [5] |
|
2. Class II lever |
(b) Door stopper. [4] |
|
3. Class III lever |
(c) Flagpole. [6] |
|
4. Wedge |
(d) Tongs. [3] |
|
5. Screw |
(e) Nutcracker. [2] |
|
6. Pulley |
(f) Pliers. [1] |
SHORT AND PRICISE
A. Give reasons for the following statements.
1. A boy with his heavy bag waiting at the bus stop does not work.
= A boy with his heavy bag waiting at the bus stop does not work as he is not moving.
2. An inclined plane acts as a force multiplier.
= An inclined plane acts as a force multiplier because the amount of effort needed to lift a load by an inclined plane is less than the load.
B. Show the given text in form of a flowchart.
Simple machines: types and examples
=
C. Answer in short.
1. Give an example of a situation where work is done is zero.
= When a person pushes a tree he is not doing any work as the tree is not moving.
2. Give two uses of an inclined plane.
= Children's slide in a playground and ramps for wheelchairs.
3. Give some examples where pulley is used as a simple machine.
= Well, flagpole, crane etc.
4. What is the lead of a screw?
= The linear distance covered by the screw in one complete turn (360°) is called its lead.
5. Why do we use a wedge?
= We use wedge to split or hold objects.
6. Define input energy and output energy.
= The work done on a machine is called the input energy.
The work done by a machine is called output energy.
AT LENGTH
A. Explain the following terms.
1. Work.
= Work is an action performed when the force acting on a body moves it or changes its position or shape in the direction of force acting on the body.
2. Energy.
= Energy is the ability to do work.
3. Lever.
= Lever is a rigid bar or rod that can move about a fixed support or point.
4. Fulcrum.
= The fixed support or point about which the lever rotates is called fulcrum.
5. Effort.
= Effort is the force applied on the machine.
6. Load.
= Load is the resulting force exerted by the machine.
7. Mechanical advantage.
= Mechanical advantage is the ratio of the load lifted by a machine to the effort applied to it.
B. Differentiate between the following.
1. Class I lever and class II lever.
=
|
Class I Lever |
Class II Lever |
|---|---|
|
1. The fulcrum is between the effort and the load. |
1. The load is between the fulcrum and the effort. |
|
2. Mechanical advantage can be greater than, equal to or less than 1. |
2. Mechanical advantage is always greater than 1. |
|
3. Examples – scissors, pliers, crow bar, oars of a rowing boat. |
3. Examples – Bottle opener, wheel barrow and nutcracker. |
2. Class II lever and class III lever.
=
|
Class II Lever |
Class III Lever |
|---|---|
|
1. The load is between the effort and the fulcrum. |
1. The effort is between the fulcrum and the load. |
|
2. Mechanical advantage is always greater than 1. |
2. Mechanical advantage is smaller than 1. |
|
3. Examples – Bottle opener, wheel barrow and nutcracker. |
3. Examples – Tongs, fishing rod, knife and broom. |
3. Class I lever and Class III lever.
=
|
Class I Lever |
Class III Lever |
|---|---|
|
1. The fulcrum is between the effort and the load. |
1. The effort is between the fulcrum and the load. |
|
2. Mechanical advantage can be greater than, equal to or less than 1. |
2. Mechanical advantage is smaller than 1. |
|
3. Examples – scissors, pliers, crow bar, oars of a rowing boat. |
3. Examples – Tongs, fishing rod, knife and broom. |
4. Fixed pulley and movable pulley.
=
|
Fixed Pulley |
Movable Pulley |
|---|---|
|
1. It is attached to a hook or a wall and doesn’t move. |
1. It moves with the load. |
|
2. Mechanical advantage is equal to 1. |
2. Mechanical advantage is more than 1(in ideal situation 2). |
|
3. Example – Well and flagpole. |
3. Example – Cranes. |
C. Read the given information carefully. Identify the incorrect parts of the information.
❐ Output energy is always greater than the input energy.
❐ The sharper the wedge, the difficult it is to pierce the object.
= ❐ Output energy is always less than the input energy.
❐ The sharper the wedge, the easier it is to pierce the object.
D. Answer in detail.
1. How do simple machines achieve their purpose of making work easier and faster to perform?
= Simple machines are devices or tools which help to make work easier and faster to perform. These help us to achieve our purpose in one o the following ways.
❐ By changing the direction of applied in the most appropriate direction: A simple machine like pulley makes work easier by changing the direction of force. Example - drawing water from a well.
❐ By applying force at a convenient position: A lever makes work easier by applying force at a convenient position. Example - Pliers.
❐ By multiplying the applied force: A screw jack acts as force multiplier and helps to lift a heavy load like car with less effort.
❐ By increasing the speed of the object: Wheel and axle act an speed multiplier in car. We apply force on the axle (smaller wheel) which turns only a short distance but the wheel (bigger wheel) turns much further in the same time. So the car moves faster.
2. Write a note on lever and describe its mechanical advantage.
= A lever is a rigid bar or rod that can move about a fixed support or point. This fixed support or point about which the lever rotates is called fulcrum. A lever is used to lift heavy weights with minimum amount of effort.
The distance between the fulcrum and the point where effort is applied is called the effort arm, and the distance between the fulcrum and the load is called the load arm.
Since a lever amplifies the input force, the load gets balanced by the effort applied about the fulcrum. So we have the expression;
Load 🇽 Load arm = Effort 🇽 Effort arm.
or
Load ÷ Effort = Effort arm ÷ Load arm = Mechanical Advantage (M.A.)
This shows that M.A. can be greater than 1, equal to 1 or less than 1, when effort arm is greater than, equal to or less than the load arm, respectively.
3. Discuss the various types of levers.
= ❐ Class I Lever : In class I lever, the fulcrum is between the effort and the load. A class I lever always changes the direction of force, i.e., applying a downward force (effort) on the lever results in an upward movement of the load. The mechanical advantage of class I lever can be greater than, equal to or less than 1. Scissors, pliers, crow bar, oars of a rowing boat and see-saw are some examples of class I lever.
❐ Class II Lever : In class II lever, the load is between the fulcrum and the effort. As it is clear from the figure below, the effort arm is always longer than the load arm. Therefore, the mechanical advantage is always greater than 1. Hence, it is used as a force multiplier. Some examples of class II lever are bottle opener, wheel barrow and nutcracker.
❐ Class III Lever : In class III lever, the effort is between the fulcrum and the load. Here the effort arm is smaller than the load arm. That is the input effort (E) is higher than the load (L). Therefore, its mechanical advantage is smaller than 1. However, the distance moved by the load is greater than distance moved by the effort. Hence it is used as a speed multiplier. Tongs, fishing rod, knife and broom are some examples of class III lever.
4. How does an inclined plane work as a simple machine?
= An inclined plane is a slanting surface which connects two points at different heights so that heavier objects can be moved up or down easily. An inclined plane reduces the effort needed to lift objects, but does not reduce the amounts of work.
In an inclined plane, the longer the distance of the ramp, the easier it is to do the work. However, since the distance to be covered is increased, it not takes more time. Also, the steeper the slope of the inclined plane, the more is the effort needed to push the load.
The mechanical advantage of an inclined plane is equal to the ration of the length of the inclined plane to its vertical height.
M.A. = length of the inclined plane (L) ÷ vertical height (h)
The mechanical advantage of an inclined plane is greater than 1, i.e., the amount of effort needed to lift a load by an inclined plane is less than the load. Hence, it acts as a force multiplier.
5. Discuss the types of pulleys.
= Pulleys are of two main types - fixed pulley and movable pulley.
❐ Fixed Pulley : In a fixed pulley, the pulley is attached to a hook or a wall and doesn't move. It changes the direction of the force, but does not amplify it. Well and flagpole are examples of fixed pulley. The mechanical advantage of a fixed pulley is equal to 1, i.e., the applied force is equal to the weight of the load.
❐ Movable pulley : A movable pulley moves with the load. The advantage of this pulley is that it reduces the effort used to pull the load. The movable pulley allows the effort to be less than the weight of the load, i.e., less effort is needed to pull the load. But the disadvantage of a movable pulley is that one has to push or pull the pulley up and down. Examples of movable pulley are cranes, block and tackle pulley in sailing boats, etc.
6. Write a note on wheel and axle.
= A wheel and axle arrangement consists of a wheel attached to a cylindrical rod or shaft called the axle. The wheel and the axle must move together to form a simple machine. The effort applied to the wheel helps in turning the axle and vice versa. The wheel and axle arrangement is used either as a force multiplier like in a doorknob or steering wheel, or as a speed multiplier as in a bicycle or tyres of a car or a truck.
When this arrangement is used as a force multiplier, on turning the large wheel the axle moves with more force. In this way one can turn heavy objects by spinning a wheel attached to an axle which in turn is connected to the heavy object. That's how a steering wheel works in a car.
In the other case, when the axle is turned, the wheel turns really fast like in the tyres of a car, bus, etc. some other examples of wheel and axle arrangement are a Ferris wheel, a screwdriver, etc.
7. Explain the efficiency of a machine. Why is the efficiency of a machine always less than 100%?
= The work done on a machine is called the input work or input energy and the work done by a machine is called the output work or output energy. The ration of the work done by a machine to the work done on the machine is termed as the efficiency of a machine.
Efficiency = Work done by a machine ÷ Work done on a machine = Output energy ÷ Input energy
The percentage efficiency of a machine can be calculated by multiplying the efficiency with 100.
Efficiency (%) = Output energy ÷ Input energy 🇽 100
For an ideal machine, the total output energy must be equal to the total input energy. But this does not happen as some of the input energy is used up in overcoming the friction between different parts of the machine and as heat from the working parts of the machine. Therefore, output energy is always less than the input energy.
A machine with 100% efficiency is called an ideal machine. But no machines is ideal in nature. The efficiency of every machine used by us is always less than 100%. The efficiency of petrol and diesel energies are almost 50% and 40%, respectively. Similarly, only about 40% energy produced by burning coal in a power plant changes into useful output energy.
8. Why is there a need to take care of machines? How can we maintain our machines?
= We all know that machines help us in performing our tasks and making things easier for us. Therefore, we should take care of them so that they have a long life. Following are some ways in which we can maintain our machines for a longer period of time.
❐ Cover the machines when not in use.
❐ Keep the machines at clean places away from dirt and moisture. Moisture can cause rusting. Machines can also be protected from moisture by painting their surfaces.
❐ Oil or grease the parts of machines regularly. This reduces friction and avoids wear and tear of the machine.