Selina Textbook Solutions: Force | Physics Class 6 ICSE PDF Download

 Page 1


? Synposis 
? A body not changing position with time with respect to a nearby fixed object is said 
to be at rest. 
? A body changing position with time with respect to a nearby fixed object is said to 
be in motion. 
?  Force is a push or pull which can change the state of rest or motion of the body or 
can change the size and shape of the body (i.e. it can deform a body). 
? A force applied on a body can 
(a) move it, if it is not in motion 
(b) stop it, if it is moving 
(c) increase or decrease its speed 
(d) change its direction of motion 
(e) change its shape or size if it is not free to move. 
? Force is defined as that cause which changes the state of rest or the state of 
motion of a body and can also deform it. 
? A force has both the magnitude and the direction. 
? When two forces act in opposite directions, the net force is equal to the difference 
of these forces, in the direction of the bigger force. 
? When two forces act on a body which are equal in magnitude but opposite in 
direction, the net force on the body is zero. 
? Forces are of two types : 
1. contact forces and 
2. non-contact forces (or forces at a distance). 
? Contact forces are 
1. the muscular force applied as push or pull, 
2. force of friction 
3. the force of reaction normal to the surface and 
4. the force of tension in a string pulled by a load. 
? Non-contact forces are 
1. gravitational force 
2. electrostatic force and 
3. magnetic force 
? The weight of a body is the force with which the earth pulls the body. 
? The unit of weight (or force) is kgf not kg which is unit of mass. 
? Friction is a force that opposes the motion. 
? Friction always acts in a direction opposite to the direction of motion. 
? The cause of friction is the interlocking of the irregular projections on the two 
surfaces in contact. ‘ 
? The force of friction depends on: 
(a) the smoothness (or roughness) of the surfaces in contact, and 
(b) the weight of the sliding (or rolling) body. 
? The force of friction does not depend on the area of the surfaces in contact. 
? The disadvantages of friction are : 
(a) Friction opposes the motion 
(b) Friction produces heat 
Page 2


? Synposis 
? A body not changing position with time with respect to a nearby fixed object is said 
to be at rest. 
? A body changing position with time with respect to a nearby fixed object is said to 
be in motion. 
?  Force is a push or pull which can change the state of rest or motion of the body or 
can change the size and shape of the body (i.e. it can deform a body). 
? A force applied on a body can 
(a) move it, if it is not in motion 
(b) stop it, if it is moving 
(c) increase or decrease its speed 
(d) change its direction of motion 
(e) change its shape or size if it is not free to move. 
? Force is defined as that cause which changes the state of rest or the state of 
motion of a body and can also deform it. 
? A force has both the magnitude and the direction. 
? When two forces act in opposite directions, the net force is equal to the difference 
of these forces, in the direction of the bigger force. 
? When two forces act on a body which are equal in magnitude but opposite in 
direction, the net force on the body is zero. 
? Forces are of two types : 
1. contact forces and 
2. non-contact forces (or forces at a distance). 
? Contact forces are 
1. the muscular force applied as push or pull, 
2. force of friction 
3. the force of reaction normal to the surface and 
4. the force of tension in a string pulled by a load. 
? Non-contact forces are 
1. gravitational force 
2. electrostatic force and 
3. magnetic force 
? The weight of a body is the force with which the earth pulls the body. 
? The unit of weight (or force) is kgf not kg which is unit of mass. 
? Friction is a force that opposes the motion. 
? Friction always acts in a direction opposite to the direction of motion. 
? The cause of friction is the interlocking of the irregular projections on the two 
surfaces in contact. ‘ 
? The force of friction depends on: 
(a) the smoothness (or roughness) of the surfaces in contact, and 
(b) the weight of the sliding (or rolling) body. 
? The force of friction does not depend on the area of the surfaces in contact. 
? The disadvantages of friction are : 
(a) Friction opposes the motion 
(b) Friction produces heat 
(c) Friction causes wear and tear 
(d) Friction reduces efficiency 
? Friction can be reduced by 
(a) making the surfaces smooth 
(b) the use of lubricants 
(c) the use of ball bearings 
(d) streamlining the shape of the moving body. 
? The maximum force exerted by a surface on a body so long as it remains 
stationary is called the force of static friction. 
? The minimum force required to keep the body moving over a surface such that it 
moves equal distances in equal intervals of time is called the force of sliding 
friction. 
? The minimum force required to roll a body on a surface is called the force of rolling 
friction. 
? Rolling friction is less than the sliding friction and sliding friction is less than the 
static friction. 
? Friction is advantageous to us in almost all activities of our life. 
Test yourself 
A. Objective Questions 
1. Write true or false for each statement 
(a) The frictional force acts in the direction of motion of body 
Answer. False 
(b) The unit of weight is kilogram 
Answer. False 
(c) A force can change the direction of motion of a moving body. 
Answer. True 
(d) A force increases the mass of the body when applied on it. 
Answer. False 
(e) The force of friction is always disadvantageous. 
Answer. False 
(f) The sliding friction is more than the rolling friction. 
Answer. True 
Page 3


? Synposis 
? A body not changing position with time with respect to a nearby fixed object is said 
to be at rest. 
? A body changing position with time with respect to a nearby fixed object is said to 
be in motion. 
?  Force is a push or pull which can change the state of rest or motion of the body or 
can change the size and shape of the body (i.e. it can deform a body). 
? A force applied on a body can 
(a) move it, if it is not in motion 
(b) stop it, if it is moving 
(c) increase or decrease its speed 
(d) change its direction of motion 
(e) change its shape or size if it is not free to move. 
? Force is defined as that cause which changes the state of rest or the state of 
motion of a body and can also deform it. 
? A force has both the magnitude and the direction. 
? When two forces act in opposite directions, the net force is equal to the difference 
of these forces, in the direction of the bigger force. 
? When two forces act on a body which are equal in magnitude but opposite in 
direction, the net force on the body is zero. 
? Forces are of two types : 
1. contact forces and 
2. non-contact forces (or forces at a distance). 
? Contact forces are 
1. the muscular force applied as push or pull, 
2. force of friction 
3. the force of reaction normal to the surface and 
4. the force of tension in a string pulled by a load. 
? Non-contact forces are 
1. gravitational force 
2. electrostatic force and 
3. magnetic force 
? The weight of a body is the force with which the earth pulls the body. 
? The unit of weight (or force) is kgf not kg which is unit of mass. 
? Friction is a force that opposes the motion. 
? Friction always acts in a direction opposite to the direction of motion. 
? The cause of friction is the interlocking of the irregular projections on the two 
surfaces in contact. ‘ 
? The force of friction depends on: 
(a) the smoothness (or roughness) of the surfaces in contact, and 
(b) the weight of the sliding (or rolling) body. 
? The force of friction does not depend on the area of the surfaces in contact. 
? The disadvantages of friction are : 
(a) Friction opposes the motion 
(b) Friction produces heat 
(c) Friction causes wear and tear 
(d) Friction reduces efficiency 
? Friction can be reduced by 
(a) making the surfaces smooth 
(b) the use of lubricants 
(c) the use of ball bearings 
(d) streamlining the shape of the moving body. 
? The maximum force exerted by a surface on a body so long as it remains 
stationary is called the force of static friction. 
? The minimum force required to keep the body moving over a surface such that it 
moves equal distances in equal intervals of time is called the force of sliding 
friction. 
? The minimum force required to roll a body on a surface is called the force of rolling 
friction. 
? Rolling friction is less than the sliding friction and sliding friction is less than the 
static friction. 
? Friction is advantageous to us in almost all activities of our life. 
Test yourself 
A. Objective Questions 
1. Write true or false for each statement 
(a) The frictional force acts in the direction of motion of body 
Answer. False 
(b) The unit of weight is kilogram 
Answer. False 
(c) A force can change the direction of motion of a moving body. 
Answer. True 
(d) A force increases the mass of the body when applied on it. 
Answer. False 
(e) The force of friction is always disadvantageous. 
Answer. False 
(f) The sliding friction is more than the rolling friction. 
Answer. True 
(g) Liquids offer more friction than the gases. 
Answer. True 
(h) A wet oily road offers more friction than a dry rough road. 
Answer. False 
2. Fill in the blanks 
(a) Force is applied as push or pull. 
(b) On squeezing a gum tube, its shape changes. 
(c) On pulling a string, its length increases. 
(d) A moving football when kicked, its direction of motion changes. 
(e) On applying brakes on a moving car, its speed slows down. 
(f) We use ball bearings to reduce the friction. 
(g) Friction opposes the motion. 
(h) Lubricants are used to reduce friction. 
(i) Friction causes wear and tear of moving parts of machine. 
3. Match the following columns 
 
Answer. 
 
Page 4


? Synposis 
? A body not changing position with time with respect to a nearby fixed object is said 
to be at rest. 
? A body changing position with time with respect to a nearby fixed object is said to 
be in motion. 
?  Force is a push or pull which can change the state of rest or motion of the body or 
can change the size and shape of the body (i.e. it can deform a body). 
? A force applied on a body can 
(a) move it, if it is not in motion 
(b) stop it, if it is moving 
(c) increase or decrease its speed 
(d) change its direction of motion 
(e) change its shape or size if it is not free to move. 
? Force is defined as that cause which changes the state of rest or the state of 
motion of a body and can also deform it. 
? A force has both the magnitude and the direction. 
? When two forces act in opposite directions, the net force is equal to the difference 
of these forces, in the direction of the bigger force. 
? When two forces act on a body which are equal in magnitude but opposite in 
direction, the net force on the body is zero. 
? Forces are of two types : 
1. contact forces and 
2. non-contact forces (or forces at a distance). 
? Contact forces are 
1. the muscular force applied as push or pull, 
2. force of friction 
3. the force of reaction normal to the surface and 
4. the force of tension in a string pulled by a load. 
? Non-contact forces are 
1. gravitational force 
2. electrostatic force and 
3. magnetic force 
? The weight of a body is the force with which the earth pulls the body. 
? The unit of weight (or force) is kgf not kg which is unit of mass. 
? Friction is a force that opposes the motion. 
? Friction always acts in a direction opposite to the direction of motion. 
? The cause of friction is the interlocking of the irregular projections on the two 
surfaces in contact. ‘ 
? The force of friction depends on: 
(a) the smoothness (or roughness) of the surfaces in contact, and 
(b) the weight of the sliding (or rolling) body. 
? The force of friction does not depend on the area of the surfaces in contact. 
? The disadvantages of friction are : 
(a) Friction opposes the motion 
(b) Friction produces heat 
(c) Friction causes wear and tear 
(d) Friction reduces efficiency 
? Friction can be reduced by 
(a) making the surfaces smooth 
(b) the use of lubricants 
(c) the use of ball bearings 
(d) streamlining the shape of the moving body. 
? The maximum force exerted by a surface on a body so long as it remains 
stationary is called the force of static friction. 
? The minimum force required to keep the body moving over a surface such that it 
moves equal distances in equal intervals of time is called the force of sliding 
friction. 
? The minimum force required to roll a body on a surface is called the force of rolling 
friction. 
? Rolling friction is less than the sliding friction and sliding friction is less than the 
static friction. 
? Friction is advantageous to us in almost all activities of our life. 
Test yourself 
A. Objective Questions 
1. Write true or false for each statement 
(a) The frictional force acts in the direction of motion of body 
Answer. False 
(b) The unit of weight is kilogram 
Answer. False 
(c) A force can change the direction of motion of a moving body. 
Answer. True 
(d) A force increases the mass of the body when applied on it. 
Answer. False 
(e) The force of friction is always disadvantageous. 
Answer. False 
(f) The sliding friction is more than the rolling friction. 
Answer. True 
(g) Liquids offer more friction than the gases. 
Answer. True 
(h) A wet oily road offers more friction than a dry rough road. 
Answer. False 
2. Fill in the blanks 
(a) Force is applied as push or pull. 
(b) On squeezing a gum tube, its shape changes. 
(c) On pulling a string, its length increases. 
(d) A moving football when kicked, its direction of motion changes. 
(e) On applying brakes on a moving car, its speed slows down. 
(f) We use ball bearings to reduce the friction. 
(g) Friction opposes the motion. 
(h) Lubricants are used to reduce friction. 
(i) Friction causes wear and tear of moving parts of machine. 
3. Match the following columns 
 
Answer. 
 
4. Select the correct alternative  
(a) A body falls downwards because of 
1. electrical force 
2. gravitational force 
3. mechanical force 
4. magnetic force. 
(b) A force does not change 
1. mass 
2. length 
3. shape 
4. state of motion. 
(c) A force to be expressed correctly requires 
1. only the magnitude 
2. only the direction 
3. both the magnitude and direction 
4. none of the above. 
(d) Friction 
1. promotes motion 
2. opposes motion 
3. acts in the direction of motion 
4. is always a nuisance. 
(e) Friction is reduced by 
1. making the surfaces wet 
2. making the surfaces dry 
3. making the surfaces rough 
4. sprinkling sand on the surface. 
(f) Friction 
1. causes wear and tear 
2. produces heat 
3. stops a moving body 
4. has all the above disadvantages 
(g) Friction is increased if 
Page 5


? Synposis 
? A body not changing position with time with respect to a nearby fixed object is said 
to be at rest. 
? A body changing position with time with respect to a nearby fixed object is said to 
be in motion. 
?  Force is a push or pull which can change the state of rest or motion of the body or 
can change the size and shape of the body (i.e. it can deform a body). 
? A force applied on a body can 
(a) move it, if it is not in motion 
(b) stop it, if it is moving 
(c) increase or decrease its speed 
(d) change its direction of motion 
(e) change its shape or size if it is not free to move. 
? Force is defined as that cause which changes the state of rest or the state of 
motion of a body and can also deform it. 
? A force has both the magnitude and the direction. 
? When two forces act in opposite directions, the net force is equal to the difference 
of these forces, in the direction of the bigger force. 
? When two forces act on a body which are equal in magnitude but opposite in 
direction, the net force on the body is zero. 
? Forces are of two types : 
1. contact forces and 
2. non-contact forces (or forces at a distance). 
? Contact forces are 
1. the muscular force applied as push or pull, 
2. force of friction 
3. the force of reaction normal to the surface and 
4. the force of tension in a string pulled by a load. 
? Non-contact forces are 
1. gravitational force 
2. electrostatic force and 
3. magnetic force 
? The weight of a body is the force with which the earth pulls the body. 
? The unit of weight (or force) is kgf not kg which is unit of mass. 
? Friction is a force that opposes the motion. 
? Friction always acts in a direction opposite to the direction of motion. 
? The cause of friction is the interlocking of the irregular projections on the two 
surfaces in contact. ‘ 
? The force of friction depends on: 
(a) the smoothness (or roughness) of the surfaces in contact, and 
(b) the weight of the sliding (or rolling) body. 
? The force of friction does not depend on the area of the surfaces in contact. 
? The disadvantages of friction are : 
(a) Friction opposes the motion 
(b) Friction produces heat 
(c) Friction causes wear and tear 
(d) Friction reduces efficiency 
? Friction can be reduced by 
(a) making the surfaces smooth 
(b) the use of lubricants 
(c) the use of ball bearings 
(d) streamlining the shape of the moving body. 
? The maximum force exerted by a surface on a body so long as it remains 
stationary is called the force of static friction. 
? The minimum force required to keep the body moving over a surface such that it 
moves equal distances in equal intervals of time is called the force of sliding 
friction. 
? The minimum force required to roll a body on a surface is called the force of rolling 
friction. 
? Rolling friction is less than the sliding friction and sliding friction is less than the 
static friction. 
? Friction is advantageous to us in almost all activities of our life. 
Test yourself 
A. Objective Questions 
1. Write true or false for each statement 
(a) The frictional force acts in the direction of motion of body 
Answer. False 
(b) The unit of weight is kilogram 
Answer. False 
(c) A force can change the direction of motion of a moving body. 
Answer. True 
(d) A force increases the mass of the body when applied on it. 
Answer. False 
(e) The force of friction is always disadvantageous. 
Answer. False 
(f) The sliding friction is more than the rolling friction. 
Answer. True 
(g) Liquids offer more friction than the gases. 
Answer. True 
(h) A wet oily road offers more friction than a dry rough road. 
Answer. False 
2. Fill in the blanks 
(a) Force is applied as push or pull. 
(b) On squeezing a gum tube, its shape changes. 
(c) On pulling a string, its length increases. 
(d) A moving football when kicked, its direction of motion changes. 
(e) On applying brakes on a moving car, its speed slows down. 
(f) We use ball bearings to reduce the friction. 
(g) Friction opposes the motion. 
(h) Lubricants are used to reduce friction. 
(i) Friction causes wear and tear of moving parts of machine. 
3. Match the following columns 
 
Answer. 
 
4. Select the correct alternative  
(a) A body falls downwards because of 
1. electrical force 
2. gravitational force 
3. mechanical force 
4. magnetic force. 
(b) A force does not change 
1. mass 
2. length 
3. shape 
4. state of motion. 
(c) A force to be expressed correctly requires 
1. only the magnitude 
2. only the direction 
3. both the magnitude and direction 
4. none of the above. 
(d) Friction 
1. promotes motion 
2. opposes motion 
3. acts in the direction of motion 
4. is always a nuisance. 
(e) Friction is reduced by 
1. making the surfaces wet 
2. making the surfaces dry 
3. making the surfaces rough 
4. sprinkling sand on the surface. 
(f) Friction 
1. causes wear and tear 
2. produces heat 
3. stops a moving body 
4. has all the above disadvantages 
(g) Friction is increased if 
1. an oil is sprayed 
2. the surfaces are made wet 
3. the surfaces are made dry 
4. the surfaces are polished 
B. Short/Long Answer Questions 
Question 1. 
Name the term used for the push or pull ? 
Answer: 
Force 
Question 2. 
Give one example each of a force as 
1. a push 
2. as pull 
3. a stretch and 
4. a squeeze. 
Answer: 
1. a push — To1 open a door, we push it. 
2. as pull — To move a grass roller on a lawn, it is pulled by a gardener. 
3. a stretch — Stretching a rubber string. 
4. a squeeze —Change in shape of a sponge on squeezing. 
Question 3. 
Explain the meaning of the term force. 
Answer: 
Force: Force is a physical cause that changes or may tend to change the state of rest 
or the state of motion of an object. The S.I. unit of force is Newton. 
Question 4. 
What effect can a force have on a stationary body ? 
Answer: 
When a force is applied on a stationary body, it begins to move. 
Question 5. 
What effects can a force have on a moving body ? 
Answer: 
When a force is applied on a moving body, it can be made to stop or it can change the 
direction of motion.