Chapter 12
Friction
Here is the answer of chapter 12 FRICTION of NCERT science of class 8.The complete solution of CHAPTER 12 FRICTION is given here which is prepared subject expert. Some important extra questions are also given with their answers.
Textbook Questions
Ques1 Fill in the blanks.
(a) Friction opposes the ________between the surfaces in contact with each other.
b)Friction depends on the ________of surfaces.
c)Friction produces __________.
d) Sprinkling of powder on the carrom board ______ friction.
e) Sliding friction is ________than the static friction.
Answers.
a)Motion
b)nature
c)heat
d )Reduces
e) Less
Ques2. Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order.Their arrangements are given below. Choose the correct arrangement.
a) Rolling, static, sliding
(b) Rolling, sliding, static
c) Static, sliding, rolling
(d) Sliding, static, rolling
c) Static, sliding, rolling
(d) Sliding, static, rolling
Ans2.c) static,sliding,rolling
Static friction is greater than the sliding friction and sliding friction is greater than the rolling friction.
Ques3 .Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor . The force of friction acting on the car on different surfaces in increasing order will be
(a) Wet marble floor, dry marble floor, newspaper, towel
(b) Newspaper, towel, dry marble floor, wet marble floor
c)Towel, newspaper, dry marble floor, wet marble floor
(d) Wet marble floor, dry marble floor, towel, newspaper
Ans3(a) Wet marble floor, dry marble floor, newspaper, towel
The force of friction acting on the car will be the maximum on the towel and minimum on the wet marble floor. The force of friction acting on the car increases gradually from wet marble floor to dry marble floor, newspaper and towel spread on the floor. Hence, the increasing order of frictional force is wet marble floor, dry marble floor, newspaper and towel.
Ques 4 .Suppose your writing desk is tilted a little.A book kept on it starts sliding down show the direction of friction force acting on it.
Ans 4. When the book is placed on the top of a tilted desk. It starts sliding down and the direction of frictional force acting on it is upwards along the surface of the desk.
Ques 5. You spill a bucket of soapy water on a marble floor accidently.Would it make it easier or more difficult for you to walk on the floor?Why?
Ans 5. When you spill a bucket of soapy water on the marble floor it makes walking on the floor more difficult. The soapy water reduces the friction between the feet and the floor due to which the feet do not get the necessary grip to walk on the floor.
Ques6 Explain why sportsman use shoes with spikes.
Ans 6. Sportsman uses shoes with spikes to get the better grip on the ground. The spikes at the bottom of the shoes increase the friction between shoes and the ground which provides the required grip.
Ques 7. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?
Ans 7. Iqbal and Seema are pushing similar boxes but of different weight on the same floor. The force required to push the forces depends on their weight because the frictional force on the surface is directly proportional to its weight. More is the weight of the box, greater is the force required to push it. Hence, Seema will have to apply more force to push the box.
Ques 8. Explain why sliding friction is less than static friction.
Ans 8. To move a surface over another surface, the interlocking of the irregularities between the surface will be smoothened, reducing the friction. Hence, sliding friction is less than static friction.
Ques 9.Give examples to show that friction is both a friend or a foe.
Ans 9. The friction between feet and the ground help us to walk, similarly the friction between our hands and object provides a grip to hold them and the friction between a chalk and a board help us to write on the board. Friction causes a great wear and tear of the surface in contact. Hence, friction is both a friend or a foe.
Ques 10.Explain why objects moving in fluids must have special shapes
Ans 10. The frictional force on an object in the fluids which is referred to as drag depends upon the nature of the fluids and the shape of the object. The object which has steamlined shape have less friction in a given fluid. Hence, the object moving in the fluid must have special shapes to reduce friction due to fluids.
(b) Newspaper, towel, dry marble floor, wet marble floor
c)Towel, newspaper, dry marble floor, wet marble floor
(d) Wet marble floor, dry marble floor, towel, newspaper
Ans3(a) Wet marble floor, dry marble floor, newspaper, towel
The force of friction acting on the car will be the maximum on the towel and minimum on the wet marble floor. The force of friction acting on the car increases gradually from wet marble floor to dry marble floor, newspaper and towel spread on the floor. Hence, the increasing order of frictional force is wet marble floor, dry marble floor, newspaper and towel.
Ques 4 .Suppose your writing desk is tilted a little.A book kept on it starts sliding down show the direction of friction force acting on it.
Ans 4. When the book is placed on the top of a tilted desk. It starts sliding down and the direction of frictional force acting on it is upwards along the surface of the desk.
Ques 5. You spill a bucket of soapy water on a marble floor accidently.Would it make it easier or more difficult for you to walk on the floor?Why?
Ans 5. When you spill a bucket of soapy water on the marble floor it makes walking on the floor more difficult. The soapy water reduces the friction between the feet and the floor due to which the feet do not get the necessary grip to walk on the floor.
Ques6 Explain why sportsman use shoes with spikes.
Ans 6. Sportsman uses shoes with spikes to get the better grip on the ground. The spikes at the bottom of the shoes increase the friction between shoes and the ground which provides the required grip.
Ques 7. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?
Ans 7. Iqbal and Seema are pushing similar boxes but of different weight on the same floor. The force required to push the forces depends on their weight because the frictional force on the surface is directly proportional to its weight. More is the weight of the box, greater is the force required to push it. Hence, Seema will have to apply more force to push the box.
Ques 8. Explain why sliding friction is less than static friction.
Ans 8. To move a surface over another surface, the interlocking of the irregularities between the surface will be smoothened, reducing the friction. Hence, sliding friction is less than static friction.
Ques 9.Give examples to show that friction is both a friend or a foe.
Ans 9. The friction between feet and the ground help us to walk, similarly the friction between our hands and object provides a grip to hold them and the friction between a chalk and a board help us to write on the board. Friction causes a great wear and tear of the surface in contact. Hence, friction is both a friend or a foe.
Ques 10.Explain why objects moving in fluids must have special shapes
Ans 10. The frictional force on an object in the fluids which is referred to as drag depends upon the nature of the fluids and the shape of the object. The object which has steamlined shape have less friction in a given fluid. Hence, the object moving in the fluid must have special shapes to reduce friction due to fluids.
This is the complete solution of CHAPTER 12 FRICTION. This is according to latest syllabus of CBSE 2020-21.
Here's some extra questions are given according to CHAPTER 11 FRICTION of class 8 Science NCERT.
Extra question /answers
Ques 1. What do you mean by the term of friction? What is the cause of friction?
Ans 1. If a body exerts a force on another body placed in its contact in a direction parallel to the contact force, the force is called the force of friction.
The friction is caused by irregularities on the two surface in contact even those surfaces which appears very smooth have large number of minute irregularities.
Ques 2. Write the properties of friction?
Ans 2 .1)Friction is produced only when one body is made to move upon the another body.
2)It always tries to prevent movement and tries to stop the body.
3)It wears the surface of contact of 2 bodies.
4)It is always in the direction opposite to the direction of motion.
Ques 3 .What are the types of friction?
Ans 3. Friction is of three types:-
1) Static friction:- When we apply a force on a body to make it move the force applied is balanced by the force of friction such force of friction is called static friction.
2) Sliding friction:- The force of friction acting between the two surfaces when one of them just slides over another surface with a uniform speed is called sliding friction.
3) Rolling friction:- When a body is placed over the other body like a roller or a wheel and is allowed to move this is called rolling function.
Example:-The suitcases and travelling bags are provided with small wheels.
Ques 4. What is a drag?
Ans 4.The frictional force exerted by fluids is known as drag.
Ques 5. Write five advantages of friction?
Ans 5. 1)Friction help us in running and Walking.
2)Friction helps in writing and making drawings.
3)Friction produces heat, a matchstick lights up due to the friction against the side of match box.
4)Wood can be cut because of friction between the axe and wood.
5)The shoes of athlete are provided with spikes to prevent slipping.
Ques 6. What is a lubricant?
Ans 6. A material which reduces the force of friction when applied between two surfaces in contact is known as lubricant.
Ques 7.why is it difficult to climb a greasy pole?
Ans 7. It is difficult to climb a greasy pole because grease reduces friction so there will be less friction between the hands and feat of the person climbing the pole.
Ques 8.Why old and smooth tyres discarded?
Ans 8. Old and smooth tyres are discarded because their surface is wear out which makes the tyres more slippery.
Ques 9.Why we sprinkle talcume powder on a carrom board?
Ans 9.When we sprinkle talcume powder on a carrom board the depressions on the surface of the board and coins of carrom get filled with powder which makes the surface smoother and reduces friction, between the board and coins of carrom.
Ques 10. Why aeroplanes and ships body is streamlined?
Ans 10. Friction due to air or water is reduced by using streamlined shapes in aeroplanes or ships. A streamlined shape is narrow in front and broader at the back.
Extra question /answers
Ques 1. What do you mean by the term of friction? What is the cause of friction?
Ans 1. If a body exerts a force on another body placed in its contact in a direction parallel to the contact force, the force is called the force of friction.
The friction is caused by irregularities on the two surface in contact even those surfaces which appears very smooth have large number of minute irregularities.
Ques 2. Write the properties of friction?
Ans 2 .1)Friction is produced only when one body is made to move upon the another body.
2)It always tries to prevent movement and tries to stop the body.
3)It wears the surface of contact of 2 bodies.
4)It is always in the direction opposite to the direction of motion.
Ques 3 .What are the types of friction?
Ans 3. Friction is of three types:-
1) Static friction:- When we apply a force on a body to make it move the force applied is balanced by the force of friction such force of friction is called static friction.
2) Sliding friction:- The force of friction acting between the two surfaces when one of them just slides over another surface with a uniform speed is called sliding friction.
3) Rolling friction:- When a body is placed over the other body like a roller or a wheel and is allowed to move this is called rolling function.
Example:-The suitcases and travelling bags are provided with small wheels.
Ques 4. What is a drag?
Ans 4.The frictional force exerted by fluids is known as drag.
Ques 5. Write five advantages of friction?
Ans 5. 1)Friction help us in running and Walking.
2)Friction helps in writing and making drawings.
3)Friction produces heat, a matchstick lights up due to the friction against the side of match box.
4)Wood can be cut because of friction between the axe and wood.
5)The shoes of athlete are provided with spikes to prevent slipping.
Ques 6. What is a lubricant?
Ans 6. A material which reduces the force of friction when applied between two surfaces in contact is known as lubricant.
Ques 7.why is it difficult to climb a greasy pole?
Ans 7. It is difficult to climb a greasy pole because grease reduces friction so there will be less friction between the hands and feat of the person climbing the pole.
Ques 8.Why old and smooth tyres discarded?
Ans 8. Old and smooth tyres are discarded because their surface is wear out which makes the tyres more slippery.
Ques 9.Why we sprinkle talcume powder on a carrom board?
Ans 9.When we sprinkle talcume powder on a carrom board the depressions on the surface of the board and coins of carrom get filled with powder which makes the surface smoother and reduces friction, between the board and coins of carrom.
Ques 10. Why aeroplanes and ships body is streamlined?
Ans 10. Friction due to air or water is reduced by using streamlined shapes in aeroplanes or ships. A streamlined shape is narrow in front and broader at the back.
These are some extra Questions of Chapter 11 FRICTION of class 8 Science NCERT.
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