Selina Textbook Solutions: Simple Machines | Physics Class 6 ICSE PDF Download

 Page 1


? Synposis 
? Work is said to be done when a force applied on a body moves it. If the body does 
not move on applying a force on it, no work is done by the force. 
? The capacity of doing work is called energy. 
? A machine is a device which helps us to do work more easily. 
? A machine enables us to apply a less effort for a load greater than the effort or to 
apply the effort at convenient point and in a desired direction. 
? Some machines are simple and some are complex. 
? The mechanical advantage of a machine is the ratio of the load to the effort, i.e., 
Mechanical advantage = Load / Effort 
? Smaller the effort required for a certain load, greater is the mechanical advantage 
of the machine. 
? The efficiency of a machine is the ratio of the useful work done on the load by the 
machine to the work put into the machine by the effort, i.e. 
Efficiency = Work output / Work input 
? The efficiency of an ideal machine is 1 (or 100 per cent). 
? The efficiency of an actual machine is less than 1 because some part of the work 
put into the machine is lost in overcoming the friction between the moving parts of 
the machine. 
? A lever is a simple machine which we most commonly use in our daily life. It is a 
rod which can turn about a fixed point called the fulcrum. 
? The mechanical advantage of a lever is equal to the ratio of the effort arm to the 
load arm, i.e. Mechanical advantage of a lever = Effort arm / Load arm 
The levers are of three kinds : 
Class I levers which have fulcrum in between the load and the effort. 
Class II levers which have load in between fulcrum and the effort. 
Class III levers which have effort in between the fulcrum and the load. 
? The mechanical advantage of class I lever can be 1, more than 1 or less than 1. 
? The mechanical advantage of class II levers is always more than 1. 
? The mechanical advantage of class III levers is always less than 1. 
? A pulley is a simple machine which is used for raising a load up by applying the 
effort downwards. 
? The mechanical advantage of an ideal pulley is 1. In an actual pulley, due to 
friction, the mechanical advantage is less than 1 (i.e., the effort is more than the 
load). 
? The pulley allow us to apply the effort downwards which is a convenient direction. 
? The wheel and axle is a simple machine having a wheel and an axle. The linear 
motion of axle is obtained by rotating the wheel so as to reduce friction. Example: 
Steering wheel, screw drivers, water tap etc. 
? An inclined plane is a simple machine which is used to move a load up with a less 
effort. It is a sloping (or slanting) surface. 
? Less the slope of the inclined plane, less is the effort needed to push a load up. 
? The mechanical advantage of an inclined plane is greater than 1 (i. e. a less effort 
is required to push a heavy load up an inclined plane). 
? A wedge is a sharp edge formed by joining the two inclined planes 
together. Example: nail, knife, axe, plough etc. 
Page 2


? Synposis 
? Work is said to be done when a force applied on a body moves it. If the body does 
not move on applying a force on it, no work is done by the force. 
? The capacity of doing work is called energy. 
? A machine is a device which helps us to do work more easily. 
? A machine enables us to apply a less effort for a load greater than the effort or to 
apply the effort at convenient point and in a desired direction. 
? Some machines are simple and some are complex. 
? The mechanical advantage of a machine is the ratio of the load to the effort, i.e., 
Mechanical advantage = Load / Effort 
? Smaller the effort required for a certain load, greater is the mechanical advantage 
of the machine. 
? The efficiency of a machine is the ratio of the useful work done on the load by the 
machine to the work put into the machine by the effort, i.e. 
Efficiency = Work output / Work input 
? The efficiency of an ideal machine is 1 (or 100 per cent). 
? The efficiency of an actual machine is less than 1 because some part of the work 
put into the machine is lost in overcoming the friction between the moving parts of 
the machine. 
? A lever is a simple machine which we most commonly use in our daily life. It is a 
rod which can turn about a fixed point called the fulcrum. 
? The mechanical advantage of a lever is equal to the ratio of the effort arm to the 
load arm, i.e. Mechanical advantage of a lever = Effort arm / Load arm 
The levers are of three kinds : 
Class I levers which have fulcrum in between the load and the effort. 
Class II levers which have load in between fulcrum and the effort. 
Class III levers which have effort in between the fulcrum and the load. 
? The mechanical advantage of class I lever can be 1, more than 1 or less than 1. 
? The mechanical advantage of class II levers is always more than 1. 
? The mechanical advantage of class III levers is always less than 1. 
? A pulley is a simple machine which is used for raising a load up by applying the 
effort downwards. 
? The mechanical advantage of an ideal pulley is 1. In an actual pulley, due to 
friction, the mechanical advantage is less than 1 (i.e., the effort is more than the 
load). 
? The pulley allow us to apply the effort downwards which is a convenient direction. 
? The wheel and axle is a simple machine having a wheel and an axle. The linear 
motion of axle is obtained by rotating the wheel so as to reduce friction. Example: 
Steering wheel, screw drivers, water tap etc. 
? An inclined plane is a simple machine which is used to move a load up with a less 
effort. It is a sloping (or slanting) surface. 
? Less the slope of the inclined plane, less is the effort needed to push a load up. 
? The mechanical advantage of an inclined plane is greater than 1 (i. e. a less effort 
is required to push a heavy load up an inclined plane). 
? A wedge is a sharp edge formed by joining the two inclined planes 
together. Example: nail, knife, axe, plough etc. 
? A screw is a modified form of an inclined plane. 
? A screwjack is a simple machine having a combination of a screw and a lever. It is 
used to lift the heavy vehicles such as cars, trucks, buses etc. 
? Machines are used for our convenience. Therefore, we should take proper care of 
a machine by painting the machine parts to avoid rusting, lubricating its parts to 
reduce friction etc. This increases the life span of the machine. 
Test yourself 
A. Objective Questions 
1. State whether the following statements are True or False. 
(a) A boy does work while pushing a wall. 
Answer. False 
Test yourself 
A. Objective Questions 
1. State whether the following statements are True or False. 
(a) A boy does work while pushing a wall. 
Answer. False 
(b) A machine performs work by itself. 
Answer. False 
(c) In an ideal machine, work done on load is equal to the work done by effort. 
Answer. True 
(d) All levers are force multipliers. 
Answer. False 
(e) A pulley changes the direction of force. 
Answer. True 
(f) An inclined plane always has the mechanical advantage more than 1. 
Answer. True 
2. Fill in the blanks 
Page 3


? Synposis 
? Work is said to be done when a force applied on a body moves it. If the body does 
not move on applying a force on it, no work is done by the force. 
? The capacity of doing work is called energy. 
? A machine is a device which helps us to do work more easily. 
? A machine enables us to apply a less effort for a load greater than the effort or to 
apply the effort at convenient point and in a desired direction. 
? Some machines are simple and some are complex. 
? The mechanical advantage of a machine is the ratio of the load to the effort, i.e., 
Mechanical advantage = Load / Effort 
? Smaller the effort required for a certain load, greater is the mechanical advantage 
of the machine. 
? The efficiency of a machine is the ratio of the useful work done on the load by the 
machine to the work put into the machine by the effort, i.e. 
Efficiency = Work output / Work input 
? The efficiency of an ideal machine is 1 (or 100 per cent). 
? The efficiency of an actual machine is less than 1 because some part of the work 
put into the machine is lost in overcoming the friction between the moving parts of 
the machine. 
? A lever is a simple machine which we most commonly use in our daily life. It is a 
rod which can turn about a fixed point called the fulcrum. 
? The mechanical advantage of a lever is equal to the ratio of the effort arm to the 
load arm, i.e. Mechanical advantage of a lever = Effort arm / Load arm 
The levers are of three kinds : 
Class I levers which have fulcrum in between the load and the effort. 
Class II levers which have load in between fulcrum and the effort. 
Class III levers which have effort in between the fulcrum and the load. 
? The mechanical advantage of class I lever can be 1, more than 1 or less than 1. 
? The mechanical advantage of class II levers is always more than 1. 
? The mechanical advantage of class III levers is always less than 1. 
? A pulley is a simple machine which is used for raising a load up by applying the 
effort downwards. 
? The mechanical advantage of an ideal pulley is 1. In an actual pulley, due to 
friction, the mechanical advantage is less than 1 (i.e., the effort is more than the 
load). 
? The pulley allow us to apply the effort downwards which is a convenient direction. 
? The wheel and axle is a simple machine having a wheel and an axle. The linear 
motion of axle is obtained by rotating the wheel so as to reduce friction. Example: 
Steering wheel, screw drivers, water tap etc. 
? An inclined plane is a simple machine which is used to move a load up with a less 
effort. It is a sloping (or slanting) surface. 
? Less the slope of the inclined plane, less is the effort needed to push a load up. 
? The mechanical advantage of an inclined plane is greater than 1 (i. e. a less effort 
is required to push a heavy load up an inclined plane). 
? A wedge is a sharp edge formed by joining the two inclined planes 
together. Example: nail, knife, axe, plough etc. 
? A screw is a modified form of an inclined plane. 
? A screwjack is a simple machine having a combination of a screw and a lever. It is 
used to lift the heavy vehicles such as cars, trucks, buses etc. 
? Machines are used for our convenience. Therefore, we should take proper care of 
a machine by painting the machine parts to avoid rusting, lubricating its parts to 
reduce friction etc. This increases the life span of the machine. 
Test yourself 
A. Objective Questions 
1. State whether the following statements are True or False. 
(a) A boy does work while pushing a wall. 
Answer. False 
Test yourself 
A. Objective Questions 
1. State whether the following statements are True or False. 
(a) A boy does work while pushing a wall. 
Answer. False 
(b) A machine performs work by itself. 
Answer. False 
(c) In an ideal machine, work done on load is equal to the work done by effort. 
Answer. True 
(d) All levers are force multipliers. 
Answer. False 
(e) A pulley changes the direction of force. 
Answer. True 
(f) An inclined plane always has the mechanical advantage more than 1. 
Answer. True 
2. Fill in the blanks 
(a) The useful work done by an actual machine is always less than the work done on 
the machine. 
(b) In class II levers, the load is in between fulcrum and effort. 
(c) The mechanical advantage of class III lever is always less than 1. 
(d) A pulley is used to change the direction of effort. 
(e) Mechanical advantage of an inclined plane is always greater than 1. 
3. Match the following 
 
Answer. 
 
 
4. Select the correct alternatives 
(a) For an ideal machine, the efficiency is 
1. greater than unity 
2. less thaii unity 
3. equalto unity 
4. depends on the value of load 
(b) Mechanical advantage of a machine is defined as: 
1. Load X Effort 
Page 4


? Synposis 
? Work is said to be done when a force applied on a body moves it. If the body does 
not move on applying a force on it, no work is done by the force. 
? The capacity of doing work is called energy. 
? A machine is a device which helps us to do work more easily. 
? A machine enables us to apply a less effort for a load greater than the effort or to 
apply the effort at convenient point and in a desired direction. 
? Some machines are simple and some are complex. 
? The mechanical advantage of a machine is the ratio of the load to the effort, i.e., 
Mechanical advantage = Load / Effort 
? Smaller the effort required for a certain load, greater is the mechanical advantage 
of the machine. 
? The efficiency of a machine is the ratio of the useful work done on the load by the 
machine to the work put into the machine by the effort, i.e. 
Efficiency = Work output / Work input 
? The efficiency of an ideal machine is 1 (or 100 per cent). 
? The efficiency of an actual machine is less than 1 because some part of the work 
put into the machine is lost in overcoming the friction between the moving parts of 
the machine. 
? A lever is a simple machine which we most commonly use in our daily life. It is a 
rod which can turn about a fixed point called the fulcrum. 
? The mechanical advantage of a lever is equal to the ratio of the effort arm to the 
load arm, i.e. Mechanical advantage of a lever = Effort arm / Load arm 
The levers are of three kinds : 
Class I levers which have fulcrum in between the load and the effort. 
Class II levers which have load in between fulcrum and the effort. 
Class III levers which have effort in between the fulcrum and the load. 
? The mechanical advantage of class I lever can be 1, more than 1 or less than 1. 
? The mechanical advantage of class II levers is always more than 1. 
? The mechanical advantage of class III levers is always less than 1. 
? A pulley is a simple machine which is used for raising a load up by applying the 
effort downwards. 
? The mechanical advantage of an ideal pulley is 1. In an actual pulley, due to 
friction, the mechanical advantage is less than 1 (i.e., the effort is more than the 
load). 
? The pulley allow us to apply the effort downwards which is a convenient direction. 
? The wheel and axle is a simple machine having a wheel and an axle. The linear 
motion of axle is obtained by rotating the wheel so as to reduce friction. Example: 
Steering wheel, screw drivers, water tap etc. 
? An inclined plane is a simple machine which is used to move a load up with a less 
effort. It is a sloping (or slanting) surface. 
? Less the slope of the inclined plane, less is the effort needed to push a load up. 
? The mechanical advantage of an inclined plane is greater than 1 (i. e. a less effort 
is required to push a heavy load up an inclined plane). 
? A wedge is a sharp edge formed by joining the two inclined planes 
together. Example: nail, knife, axe, plough etc. 
? A screw is a modified form of an inclined plane. 
? A screwjack is a simple machine having a combination of a screw and a lever. It is 
used to lift the heavy vehicles such as cars, trucks, buses etc. 
? Machines are used for our convenience. Therefore, we should take proper care of 
a machine by painting the machine parts to avoid rusting, lubricating its parts to 
reduce friction etc. This increases the life span of the machine. 
Test yourself 
A. Objective Questions 
1. State whether the following statements are True or False. 
(a) A boy does work while pushing a wall. 
Answer. False 
Test yourself 
A. Objective Questions 
1. State whether the following statements are True or False. 
(a) A boy does work while pushing a wall. 
Answer. False 
(b) A machine performs work by itself. 
Answer. False 
(c) In an ideal machine, work done on load is equal to the work done by effort. 
Answer. True 
(d) All levers are force multipliers. 
Answer. False 
(e) A pulley changes the direction of force. 
Answer. True 
(f) An inclined plane always has the mechanical advantage more than 1. 
Answer. True 
2. Fill in the blanks 
(a) The useful work done by an actual machine is always less than the work done on 
the machine. 
(b) In class II levers, the load is in between fulcrum and effort. 
(c) The mechanical advantage of class III lever is always less than 1. 
(d) A pulley is used to change the direction of effort. 
(e) Mechanical advantage of an inclined plane is always greater than 1. 
3. Match the following 
 
Answer. 
 
 
4. Select the correct alternatives 
(a) For an ideal machine, the efficiency is 
1. greater than unity 
2. less thaii unity 
3. equalto unity 
4. depends on the value of load 
(b) Mechanical advantage of a machine is defined as: 
1. Load X Effort 
2. Load / Effort 
3. Load + Effort 
4. Effort / Load 
(c) The mechanical advantage of a lever is equal to: 
1. Load arm / Effort arm 
2. Effort arm / Load arm 
3. Load arm + Effortarm 
4. Load ann — Effort arm 
(d) A pulley is used because it 
1. has the mechanical advantage greatcr than one 
2. has 100% efficiency 
3. helps to apply the force in a convenient direction 
4. requires more effort to raise a less load. 
(e) Wheel is used with axle because 
1. sliding friction is less than the roffing friction 
2. rolling friction is less than the sliding friction 
3. they work as the inclined plane 
4. They help us to change the direction of force. 
B. Short/Long Answer Questions 
Question 1. 
When is work said to be done by a force? 
Answer: 
Work is said to be done when a force moves an obj ect through a distance in its own 
direction. 
Question 2. 
What is energy? 
Answer: 
Energy: The ability or capacity to do work is called energy. 
Question 3. 
What do you understand by a machine? 
Answer: 
Machine: A machine is a device that allows us to do work with less effort. Machines 
make our work easier to do. Machines have made our li ves comfortable and faster. 
Page 5


? Synposis 
? Work is said to be done when a force applied on a body moves it. If the body does 
not move on applying a force on it, no work is done by the force. 
? The capacity of doing work is called energy. 
? A machine is a device which helps us to do work more easily. 
? A machine enables us to apply a less effort for a load greater than the effort or to 
apply the effort at convenient point and in a desired direction. 
? Some machines are simple and some are complex. 
? The mechanical advantage of a machine is the ratio of the load to the effort, i.e., 
Mechanical advantage = Load / Effort 
? Smaller the effort required for a certain load, greater is the mechanical advantage 
of the machine. 
? The efficiency of a machine is the ratio of the useful work done on the load by the 
machine to the work put into the machine by the effort, i.e. 
Efficiency = Work output / Work input 
? The efficiency of an ideal machine is 1 (or 100 per cent). 
? The efficiency of an actual machine is less than 1 because some part of the work 
put into the machine is lost in overcoming the friction between the moving parts of 
the machine. 
? A lever is a simple machine which we most commonly use in our daily life. It is a 
rod which can turn about a fixed point called the fulcrum. 
? The mechanical advantage of a lever is equal to the ratio of the effort arm to the 
load arm, i.e. Mechanical advantage of a lever = Effort arm / Load arm 
The levers are of three kinds : 
Class I levers which have fulcrum in between the load and the effort. 
Class II levers which have load in between fulcrum and the effort. 
Class III levers which have effort in between the fulcrum and the load. 
? The mechanical advantage of class I lever can be 1, more than 1 or less than 1. 
? The mechanical advantage of class II levers is always more than 1. 
? The mechanical advantage of class III levers is always less than 1. 
? A pulley is a simple machine which is used for raising a load up by applying the 
effort downwards. 
? The mechanical advantage of an ideal pulley is 1. In an actual pulley, due to 
friction, the mechanical advantage is less than 1 (i.e., the effort is more than the 
load). 
? The pulley allow us to apply the effort downwards which is a convenient direction. 
? The wheel and axle is a simple machine having a wheel and an axle. The linear 
motion of axle is obtained by rotating the wheel so as to reduce friction. Example: 
Steering wheel, screw drivers, water tap etc. 
? An inclined plane is a simple machine which is used to move a load up with a less 
effort. It is a sloping (or slanting) surface. 
? Less the slope of the inclined plane, less is the effort needed to push a load up. 
? The mechanical advantage of an inclined plane is greater than 1 (i. e. a less effort 
is required to push a heavy load up an inclined plane). 
? A wedge is a sharp edge formed by joining the two inclined planes 
together. Example: nail, knife, axe, plough etc. 
? A screw is a modified form of an inclined plane. 
? A screwjack is a simple machine having a combination of a screw and a lever. It is 
used to lift the heavy vehicles such as cars, trucks, buses etc. 
? Machines are used for our convenience. Therefore, we should take proper care of 
a machine by painting the machine parts to avoid rusting, lubricating its parts to 
reduce friction etc. This increases the life span of the machine. 
Test yourself 
A. Objective Questions 
1. State whether the following statements are True or False. 
(a) A boy does work while pushing a wall. 
Answer. False 
Test yourself 
A. Objective Questions 
1. State whether the following statements are True or False. 
(a) A boy does work while pushing a wall. 
Answer. False 
(b) A machine performs work by itself. 
Answer. False 
(c) In an ideal machine, work done on load is equal to the work done by effort. 
Answer. True 
(d) All levers are force multipliers. 
Answer. False 
(e) A pulley changes the direction of force. 
Answer. True 
(f) An inclined plane always has the mechanical advantage more than 1. 
Answer. True 
2. Fill in the blanks 
(a) The useful work done by an actual machine is always less than the work done on 
the machine. 
(b) In class II levers, the load is in between fulcrum and effort. 
(c) The mechanical advantage of class III lever is always less than 1. 
(d) A pulley is used to change the direction of effort. 
(e) Mechanical advantage of an inclined plane is always greater than 1. 
3. Match the following 
 
Answer. 
 
 
4. Select the correct alternatives 
(a) For an ideal machine, the efficiency is 
1. greater than unity 
2. less thaii unity 
3. equalto unity 
4. depends on the value of load 
(b) Mechanical advantage of a machine is defined as: 
1. Load X Effort 
2. Load / Effort 
3. Load + Effort 
4. Effort / Load 
(c) The mechanical advantage of a lever is equal to: 
1. Load arm / Effort arm 
2. Effort arm / Load arm 
3. Load arm + Effortarm 
4. Load ann — Effort arm 
(d) A pulley is used because it 
1. has the mechanical advantage greatcr than one 
2. has 100% efficiency 
3. helps to apply the force in a convenient direction 
4. requires more effort to raise a less load. 
(e) Wheel is used with axle because 
1. sliding friction is less than the roffing friction 
2. rolling friction is less than the sliding friction 
3. they work as the inclined plane 
4. They help us to change the direction of force. 
B. Short/Long Answer Questions 
Question 1. 
When is work said to be done by a force? 
Answer: 
Work is said to be done when a force moves an obj ect through a distance in its own 
direction. 
Question 2. 
What is energy? 
Answer: 
Energy: The ability or capacity to do work is called energy. 
Question 3. 
What do you understand by a machine? 
Answer: 
Machine: A machine is a device that allows us to do work with less effort. Machines 
make our work easier to do. Machines have made our li ves comfortable and faster. 
Question 4. 
What is the principle on which a machine works ? 
Answer: 
Principle of a Machine: The work output of a machine is equal to the work input. 
Question 5. 
State two functions of a machine. 
Answer: 
Various functions that a machine can perform are: 
1. Changing the direction of applied force — Example: When a flag is hoisted with 
the help of a pulley. 
2. Changing the magnitude of applied force — Example: Bottle opener multiplies the 
applied force and much less effort is required to open the cap. 
3. Applying force at a convenient point — Example: In a pair of scissors, the input 
force is applied at the handle of the scissors which cuts the paper at the other end 
of the blade. 
4. Changing the speed of an object — Example: While riding a bicycle, force is 
applied on pedals which multiplies the speed. 
Question 6. 
Name six simple machines. Give an example of each machine. 
Answer: 
The Simple Machines and there examples are as follows: 
1. The lever: Examples are a crow bar, claw hammer, a pair of pilers etc. 
2. The Inclined plane: Examples are ramp, staircase, hilly roads etc. 
3. The wedge: Examples are knife, axe, plough, nail etc. 
4. Screw: Examples are A screw. 
5. The wheel and axle: Examples are steering wheel of a car, bicycle pedal etc. 
6. The pulley: Examples are a pulley used in raising a load. 
Question 7. 
Define the term ‘work input’ and ‘work output’ in relation to a machine. 
Answer: 
Work input is work done on a machine equal to the effort force times the distance 
through which the force is applied. 
Work output is work that is done by a machine equals resistance force times the 
distance through which the force applied. 
For an ideal machine, the work output is equal to the work input i. e. the efficiency. 
Question 8. 
Explain the term mechanical advantage of a machine. 
Answer: 
The mechanical advantage of a machine is the ratio of the load to tiie effort. In other