Class 8 Science Chapter 9 Friction

Chapter 9 of Class 8 Science, titled "Friction," focuses on the force that opposes the relative motion or tendency of such motion of two surfaces in contact. The chapter explores the nature of friction, its causes, and the different types of friction, including static, sliding, and rolling friction. Students will learn about the factors that affect friction, such as the nature of the surfaces in contact and the force pressing them together. The chapter also highlights both the beneficial and harmful effects of friction in everyday life—how it helps in activities like walking or driving, and how it causes wear and tear in machines and engines. Moreover, the concept of reducing friction to improve efficiency in various mechanical systems, such as using lubricants and ball bearings, is also discussed. The quiz on this chapter will assess students’ understanding of the principles of friction, its real-world applications, and its effect on motion and energy. By the end of this chapter, students will gain a deeper understanding of how friction plays a crucial role in our daily activities and in the functioning of various technologies.

1 / 100

Category: Introduction

1. Why is it difficult to walk on a smooth and wet floor?

a. Because of increased gravity

b. Because of reduced friction

c. Because of air pressure

d. Because of surface tension

2 / 100

Category: Introduction

2. If the sum of two numbers is 45 and one of them is 18, what is the other number?

a. 25

b. 27

c. 30

d. 35

3 / 100

Category: Introduction

3. What is the force that opposes the relative motion between two surfaces in contact?

a. Gravitational force

b. Magnetic force

c. Force of friction

d. Electrostatic force

4 / 100

Category: Observations of friction in daily life (slowing down vehicles, stopping objects, slipping on surfaces)

4. (A) When a book is pushed on a table, it eventually stops moving due to the force of friction.
(R) Friction acts in the opposite direction of the motion of the object.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

5 / 100

Category: Observations of friction in daily life (slowing down vehicles, stopping objects, slipping on surfaces)

5. (A) A moving ball on the ground stops eventually without any external force applied to it.
(R) Friction opposes the relative motion between the surfaces of the ball and the ground.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

6 / 100

Category: Observations of friction in daily life (slowing down vehicles, stopping objects, slipping on surfaces)

6. Why is it difficult to walk on a smooth and wet floor?

a. The floor becomes sticky \air Water increases gravitational force \air Reduced friction between shoes and floor \air The floor becomes uneven

7 / 100

Category: Understanding why friction occurs

7. Why does friction occur between two surfaces?

a. Due to gravitational force

b. Because of magnetic attraction

c. Due to interlocking of surface irregularities

d. Because of air resistance

8 / 100

Category: Understanding why friction occurs

8. (A) Static friction is greater than sliding friction.
(R) When an object starts moving, the contact points do not get enough time to interlock.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

9 / 100

Category: Understanding why friction occurs

9. What is the direction of the force of friction when an object is pushed to the left?

a. To the left

b. To the right

c. Upwards

d. Downwards

10 / 100

Category: Force of Friction

10. What is the direction of the force of friction acting on a book when it is pushed to the right on a table?

a. To the right

b. To the left

c. Upwards

d. Downwards

11 / 100

Category: Force of Friction

11. If a book stops moving after being pushed on a table, what force is responsible for bringing it to rest?

a. Gravitational force

b. Magnetic force

c. Force of friction

d. Applied force

12 / 100

Category: Force of Friction

12. (A) The force of friction always acts in the same direction as the applied force.
(R) The force of friction opposes the relative motion between the surfaces in contact.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

13 / 100

Category: Friction is a force that opposes motion

13. Which of the following factors does NOT affect the force of friction between two surfaces?

a. Nature of the surfaces in contact

b. State of smoothness of the surfaces

c. How hard the surfaces press together

d. Color of the surfaces

14 / 100

Category: Friction is a force that opposes motion

14. (A) The force of friction between two surfaces depends on the roughness of the surfaces.
(R) Friction is caused by the interlocking of irregularities on the surfaces in contact.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

15 / 100

Category: Friction is a force that opposes motion

15. What is the primary role of friction between two surfaces in contact?

a. Facilitates motion between surfaces

b. Opposes the relative motion between surfaces

c. Increases the speed of moving objects

d. Reduces the weight of objects

16 / 100

Category: It acts between surfaces in contact

16. A block of mass $m$ is placed on a horizontal surface. The coefficient of friction between the block and the surface is $\mu$. If an additional weight $M$ is placed on top of the block, how does the frictional force change?

a. The frictional force decreases.

b. The frictional force remains the same.

c. The frictional force increases.

d. The frictional force becomes zero.

17 / 100

Category: It acts between surfaces in contact

17. A block is placed on a rough horizontal surface. A force $F$ is applied to the right, causing the block to move at a constant velocity. What can be inferred about the direction and magnitude of the frictional force acting on the block?

a. The frictional force acts to the right with a magnitude less than $F$.

b. The frictional force acts to the left with a magnitude less than $F$.

c. The frictional force acts to the right with a magnitude equal to $F$.

d. The frictional force acts to the left with a magnitude equal to $F$.

18 / 100

Category: It acts between surfaces in contact

18. (A) The force of friction increases when two surfaces are pressed harder against each other.
(R) This is because the interlocking of irregularities between the surfaces becomes more pronounced with increased pressure.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

19 / 100

Category: Friction always acts in the direction opposite to motion

19. (A) When a book is pushed to the left on a table, the friction acts to the right.
(R) The force of friction always acts opposite to the direction of motion.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

20 / 100

Category: Friction always acts in the direction opposite to motion

20. A box weighing 100 N is pushed horizontally with a force of 40 N. If the coefficient of static friction between the box and the floor is 0.5, what is the maximum static friction force that can act on the box?

a. 30 N

b. 40 N

c. 50 N

d. 60 N

21 / 100

Category: Friction always acts in the direction opposite to motion

21. (A) Friction always acts in the direction opposite to the motion of an object.
(R) The force of friction opposes the applied force, which causes the motion.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

22 / 100

Category: Factors Affecting Friction

22. A pencil cell is released from point A on an inclined plane covered with cloth. How does the distance it travels before coming to rest compare to when the plane is uncovered?

a. It travels the same distance

b. It travels a longer distance

c. It travels a shorter distance

d. It stops immediately

23 / 100

Category: Factors Affecting Friction

23. (A) Sprinkling powder on a carrom board reduces friction.
(R) Powder acts as a lubricant, preventing direct contact between surfaces.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

24 / 100

Category: Factors Affecting Friction

24. Why do carrom players sprinkle fine powder on the carrom board?

a. To increase the weight of the board

b. To reduce friction

c. To make the board more colorful

d. To increase friction

25 / 100

Category: More friction on rough surfaces due to increased interlocking

25. How does increasing the pressure between two surfaces affect the force of friction?

a. The force of friction decreases.

b. The force of friction remains unchanged.

c. The force of friction increases.

d. The force of friction becomes zero.

26 / 100

Category: More friction on rough surfaces due to increased interlocking

26. How does increasing the pressure between two surfaces affect the force of friction?

a. Decreases the force of friction

b. Has no effect on the force of friction

c. Increases the force of friction

d. Eliminates the force of friction

27 / 100

Category: More friction on rough surfaces due to increased interlocking

27. (A) The force of friction is greater on rough surfaces compared to smooth surfaces.
(R) Rough surfaces have a larger number of irregularities that interlock, increasing the friction.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

28 / 100

Category: Greater force required when surfaces are pressed harder

28. Which of the following statements correctly describes static friction?

a. The force required to keep an object moving at a constant speed

b. The force that causes an object to accelerate

c. The force required to overcome friction when an object starts moving from rest

d. The force that reduces the speed of an object

29 / 100

Category: Greater force required when surfaces are pressed harder

29. What is the relationship between static friction and sliding friction?

a. Static friction is less than sliding friction

b. Static friction is equal to sliding friction

c. Static friction is greater than sliding friction

d. There is no relationship between static and sliding friction

30 / 100

Category: Greater force required when surfaces are pressed harder

30. A box is placed on a horizontal surface. When an additional weight is added to the box, the normal force increases by 50 N. How does the frictional force change if the coefficient of friction remains the same?

a. Frictional force decreases by 50 N

b. Frictional force increases by 50 N

c. Frictional force remains unchanged

d. Frictional force doubles

31 / 100

Category: Friction depends on surface texture and pressure

31. A brick is wrapped with a jute bag and pulled using a spring balance. The reading on the spring balance is noted. What would happen to the reading if the brick is wrapped with polythene instead of jute?

a. The reading increases

b. The reading remains the same

c. The reading decreases

d. The reading becomes zero

32 / 100

Category: Friction depends on surface texture and pressure

32. (A) The force of friction increases when the surfaces in contact are rougher.
(R) The roughness of the surfaces causes more interlocking of irregularities, which increases friction.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

33 / 100

Category: Friction depends on surface texture and pressure

33. Which type of friction is generally smaller: sliding friction or static friction?

a. Sliding friction

b. Static friction

c. Both are equal

d. Neither exists

34 / 100

Category: Friction: A Necessary Evil

34. What happens when you vigorously rub your palms together for a few minutes?

a. Your palms become cold

b. Your palms become slippery

c. Your palms generate heat

d. Your palms become sticky

35 / 100

Category: Friction: A Necessary Evil

35. (A) Friction is necessary for walking on a surface.
(R) Without friction, it would be impossible to walk as the feet would not grip the ground.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

36 / 100

Category: Friction: A Necessary Evil

36. (A) The force of friction increases when the surfaces in contact are pressed harder because the interlocking of irregularities becomes more pronounced.

(R) The increase in pressure between two surfaces reduces the irregularities, thereby increasing friction.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

37 / 100

Category: Friction helps in walking, writing, and holding objects

37. (A) It is easier to hold a glass tumbler with a greasy surface than a dry one.
(R) Friction decreases when the surface becomes greasy, making it harder to hold objects.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

38 / 100

Category: Friction helps in walking, writing, and holding objects

38. Why is it difficult to walk on a wet marble floor?

a. The surface becomes smoother

b. The surface becomes rougher

c. The surface becomes slippery

d. The surface becomes sticky

39 / 100

Category: Friction helps in walking, writing, and holding objects

39. Why is it harder to hold a greasy glass tumbler compared to a dry one?

a. The tumbler becomes heavier

b. The tumbler becomes lighter

c. The tumbler becomes slippery

d. The tumbler becomes more rigid

40 / 100

Category: Friction also causes wear and tear, and heat generation

40. What is one effect of friction on materials?

a. It reduces heat generation

b. It prevents wear and tear

c. It causes wear and tear

d. It eliminates friction

41 / 100

Category: Friction also causes wear and tear, and heat generation

41. Which type of friction is required to overcome when an object starts moving from rest?

a. Sliding friction

b. Rolling friction

c. Static friction

d. Fluid friction

42 / 100

Category: Friction also causes wear and tear, and heat generation

42. A machine is run for 30 minutes and due to friction, it generates heat energy of 1800 J. If the same machine is run for 45 minutes under the same conditions, what will be the heat energy generated?

a. 2700 J

b. 2400 J

c. 3000 J

d. 3600 J

43 / 100

Category: Motion of a pencil cell on different surfaces

43. If a pencil cell is wrapped with sandpaper and then rolled down an inclined plane covered with a smooth cloth, how does the distance travelled by the cell compare to when it is unwrapped and rolled down the same plane?

a. The distance increases

b. The distance decreases

c. The distance remains the same

d. The distance depends on the slope angle

44 / 100

Category: Motion of a pencil cell on different surfaces

44. A pencil cell is rolled down an inclined plane on three different surfaces: a smooth table, a cloth-covered table, and a sand-covered table. On which surface will the pencil cell travel the least distance before coming to rest?

a. Smooth table

b. Cloth-covered table

c. Sand-covered table

d. All surfaces will have the same distance

45 / 100

Category: Motion of a pencil cell on different surfaces

45. A pencil cell is released from a point on an inclined plane. It moves down the plane and then comes to rest on a table covered with a smooth cloth. If the same experiment is repeated with a sand-covered table, how does the distance covered by the pencil cell change?

a. The distance increases because of reduced friction.

b. The distance decreases because of increased friction.

c. The distance remains the same as friction does not change.

d. The distance cannot be determined without measuring.

46 / 100

Category: Examples of useful friction: writing with chalk, gripping objects

46. Why is it easier to hold a kulhar (earthen pot) than a greasy glass tumbler?

a. Because the kulhar is lighter

b. Due to the smooth surface of the glass tumbler

c. Because the kulhar has a rough surface providing more friction

d. Because the glass tumbler is made of glass

47 / 100

Category: Examples of useful friction: writing with chalk, gripping objects

47. Why is friction important when gripping objects like a glass tumbler?

a. It makes the tumbler lighter

b. It reduces the pressure needed to hold the tumbler

c. It prevents the tumbler from slipping

d. It increases the temperature of the tumbler

48 / 100

Category: Examples of useful friction: writing with chalk, gripping objects

48. When writing with chalk on a blackboard, why does the chalk leave a mark on the board?

a. Due to the smoothness of the board

b. Because of the chemical reaction between chalk and board

c. As a result of gravitational force

d. Because of friction between the chalk and the board

49 / 100

Category: Problems due to friction: worn-out shoes, overheating of machines

49. Which of the following is an example where friction produces heat?

a. Rubbing palms together

b. Ironing clothes

c. Stirring soup gently

d. Lighting a candle

50 / 100

Category: Problems due to friction: worn-out shoes, overheating of machines

50. A car's brake pads generate heat when the brakes are applied. If the friction force between the brake pads and the wheel is 200 N and the car comes to a stop from a speed of 20 m/s in 5 seconds, how much heat is generated?

a. 5,000 J

b. 10,000 J

c. 15,000 J

d. 20,000 J

51 / 100

Category: Problems due to friction: worn-out shoes, overheating of machines

51. A person walks 10,000 steps every day on a rough surface. If each step causes a wear of 0.01 mm on the shoe sole, how much will the sole wear out in one year (365 days)?

a. 3.65 m

b. 36.5 m

c. 365 m

d. 3650 m

52 / 100

Category: Activity: Rubbing hands together to generate heat

52. What happens when you rub your palms together vigorously for a few minutes?

a. Your palms become cold

b. Your palms become warm

c. Your palms start to sweat

d. Your palms remain unchanged

53 / 100

Category: Activity: Rubbing hands together to generate heat

53. When you vigorously rub your palms together, why do they feel warm?

a. Friction converts mechanical energy into sound energy

b. Friction converts mechanical energy into electrical energy

c. Friction converts mechanical energy into thermal energy

d. Friction converts mechanical energy into magnetic energy

54 / 100

Category: Activity: Rubbing hands together to generate heat

54. (A) Rubbing hands together generates heat due to friction.
(R) Friction converts mechanical energy into thermal energy.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

55 / 100

Category: Increasing and Reducing Friction

55. Why do brake pads in automobiles have a rough surface?

a. To reduce friction for smoother movement

b. To increase friction for effective braking

c. To make the brakes look stylish

d. To decrease the weight of the vehicle

56 / 100

Category: Increasing and Reducing Friction

56. (A) Gymnasts apply a coarse substance on their hands to increase friction for better grip.
(R) Increasing friction helps in providing a better grip by enhancing the interlocking of irregularities between surfaces.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

57 / 100

Category: Increasing and Reducing Friction

57. (A) The soles of shoes are grooved to increase friction.
(R) Increasing friction provides better grip on the floor, ensuring safety.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

58 / 100

Category: Increasing friction:

58. Kabaddi players often rub their hands with soil before a match. What is the primary reason for this action?

a. To reduce the friction between their hands and their opponents.

b. To make their hands slippery and avoid being caught by opponents.

c. To increase the friction between their hands and their opponents for a better grip.

d. To clean their hands before playing the game.

59 / 100

Category: Increasing friction:

59. (A) The soles of shoes are grooved to increase friction.
(R) Increased friction provides better grip on the floor.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

60 / 100

Category: Increasing friction:

60. (A) The soles of shoes are grooved to increase friction.
(R) Grooves on the soles provide a better grip on the floor, preventing slipping.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

61 / 100

Category: Grooved shoe soles and treaded tyres

61. (A) Grooved shoe soles and treaded tyres are designed to increase friction.
(R) The grooves and treads provide better grip by increasing the surface area in contact with the ground.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

62 / 100

Category: Grooved shoe soles and treaded tyres

62. (A) Grooved shoe soles and treaded tyres are designed to increase friction by increasing the surface area in contact with the ground.
(R) The increased surface area enhances the interlocking of irregularities between the surfaces, thereby increasing friction.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

63 / 100

Category: Brake pads in bicycles

63. What is the primary purpose of using brake pads in a bicycle?

a. To increase the speed of the bicycle

b. To reduce the weight of the bicycle

c. To create friction and stop the wheel

d. To improve the aerodynamics of the bicycle

64 / 100

Category: Brake pads in bicycles

64. What happens when brake pads press against the bicycle wheel rim?

a. The wheel moves faster

b. The friction reduces

c. The wheel slows down or stops

d. The bicycle accelerates

65 / 100

Category: Kabaddi players using soil for grip

65. (A) Kabaddi players use soil to increase friction for a better grip.
(R) Soil increases the roughness of the hands, which enhances friction.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

66 / 100

Category: Kabaddi players using soil for grip

66. In a bicycle brake system, the brake pads reduce the speed of the wheel by increasing friction. If the brake pads apply a normal force of 100 N and the coefficient of friction between the pads and the rim is 0.5, how much frictional force is generated to stop the wheel?

a. 30 N

b. 40 N

c. 50 N

d. 60 N

67 / 100

Category: Reducing friction:

67. Why is it easier to pull luggage fitted with rollers compared to sliding it?

a. Rolling increases friction

b. Sliding reduces friction

c. Rolling reduces friction compared to sliding

d. Sliding and rolling have the same friction

68 / 100

Category: Reducing friction:

68. Why is it easier to pull luggage fitted with rollers compared to sliding it?

a. Rolling friction is greater than sliding friction

b. Rolling friction is smaller than sliding friction

c. Sliding friction is not related to rollers

d. Rollers increase the weight of the luggage

69 / 100

Category: Lubricants like oil, grease, and graphite

69. (A) Grease is used as a lubricant in the moving parts of a bicycle to reduce friction.
(R) Grease forms a thin layer between the moving parts, preventing direct contact and reducing friction.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

70 / 100

Category: Lubricants like oil, grease, and graphite

70. Which of the following is NOT a common lubricant?

a. Grease

b. Graphite

c. Oil

d. Sugar

71 / 100

Category: Powder on carrom boards

71. (A) Sprinkling fine powder on a carrom board reduces friction.
(R) The powder acts as a lubricant by forming a thin layer between the carrom pieces and the board.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

72 / 100

Category: Powder on carrom boards

72. When oil is applied to the hinges of a door, the door moves smoothly. Which of the following principles is primarily responsible for this effect?

a. The oil increases the mass of the door

b. The oil reduces friction by acting as a lubricant

c. The oil increases the surface area of the hinges

d. The oil changes the material of the door

73 / 100

Category: Using air cushions in machines

73. In a machine using an air cushion, if the thickness of the air cushion is doubled while keeping the air pressure constant, how does this affect the friction between the moving parts?

a. Friction increases due to increased thickness

b. Friction decreases due to increased separation

c. Friction remains unchanged as thickness does not affect friction

d. Friction first decreases then increases with thickness

74 / 100

Category: Using air cushions in machines

74. What is a primary advantage of using air cushions over oil in reducing friction?

a. They are cheaper than oil

b. They provide a cleaner environment

c. They increase friction

d. They require frequent maintenance

75 / 100

Category: Wheels Reduce Friction

75. (A) The use of wheels in machinery reduces friction significantly because rolling friction is always less than sliding friction.
(R) Rolling friction occurs due to the deformation of the surfaces in contact, which minimizes the resistance to motion.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

76 / 100

Category: Wheels Reduce Friction

76. Which of the following statements is true about rolling friction?

a. It is greater than sliding friction

b. It is equal to sliding friction

c. It is always zero

d. It is less than sliding friction

77 / 100

Category: Rolling friction is much less than sliding friction

77. (A) Rolling friction is smaller than sliding friction because the contact area between the rolling object and the surface is reduced.
(R) Rolling reduces friction by converting sliding motion into rotational motion, which minimizes energy loss.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

78 / 100

Category: Rolling friction is much less than sliding friction

78. Why are wheels considered one of the greatest inventions of mankind?

a. They increase friction

b. They make objects heavier

c. They reduce friction and make movement easier

d. They eliminate the need for lubrication

79 / 100

Category: Wheels and ball bearings reduce friction

79. A heavy metal block is moved across a rough surface using two different methods: sliding and rolling with the help of ball bearings. If the force required to slide the block is 100 N, what would be the approximate force required to roll it using ball bearings, given that rolling friction is 10\% of sliding friction?

a. 5 N

b. 10 N

c. 15 N

d. 20 N

80 / 100

Category: Wheels and ball bearings reduce friction

80. (A) It is easier to pull luggage fitted with rollers than to slide it.
(R) Rolling friction is smaller than sliding friction.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

81 / 100

Category: Luggage with wheels

81. Which of the following is an example where rolling friction is utilized?

a. Sliding a book on a table

b. Pushing a heavy box across the floor

c. Using ball bearings in a bicycle's wheels

d. Walking on a rough surface

82 / 100

Category: Luggage with wheels

82. Which of the following is an example where rolling friction is utilized to reduce effort?

a. Moving a heavy box without any rollers

b. Using ball bearings in a ceiling fan

c. Pushing a car stuck in mud

d. Dragging a suitcase without wheels

83 / 100

Category: Rolling vs. sliding comparison with logs and machines

83. (A) The use of ball bearings in machines reduces friction because they convert sliding friction into rolling friction.
(R) Rolling friction is always less than sliding friction due to the reduced contact area and smoother motion.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

84 / 100

Category: Rolling vs. sliding comparison with logs and machines

84. What is the purpose of using ball bearings in machines like ceiling fans and bicycles?

a. To increase sliding friction

b. To reduce rolling friction

c. To replace sliding friction with rolling friction

d. To eliminate friction completely

85 / 100

Category: Use of ball bearings in machines and vehicles

85. (A) The use of ball bearings in machines reduces friction because they convert sliding friction into rolling friction.
(R) Rolling friction is always less than sliding friction.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

86 / 100

Category: Use of ball bearings in machines and vehicles

86. Why is rolling friction smaller than sliding friction?

a. Because rolling motion increases surface roughness

b. Because rolling motion reduces the contact area between surfaces

c. Because rolling motion eliminates all friction

d. Because rolling motion increases the weight of the object

87 / 100

Category: Fluid Friction (Drag)

87. What is the common name of gases and liquids in the context of friction?

a. Solids

b. Fluids

c. Plasma

d. Vacuum

88 / 100

Category: Fluid Friction (Drag)

88. (A) The shape of an aeroplane is designed to minimize fluid friction.
(R) Aeroplanes are given streamlined shapes inspired by the natural shapes of birds and fishes.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

89 / 100

Category: Fluids (liquids and gases) also exert friction

89. A fish swims in water. Which of the following statements is true regarding the fluid friction experienced by the fish?

a. The shape of the fish increases fluid friction

b. The shape of the fish reduces fluid friction \color{black}

c. The color of the fish affects fluid friction \color{black}

d. The size of the fish has no effect on fluid friction \color{black}

90 / 100

Category: Fluids (liquids and gases) also exert friction

90. An aeroplane is designed to have a shape similar to that of a bird. What is the primary reason for this design choice?

a. To increase the weight of the aeroplane

b. To reduce fluid friction \color{black}

c. To make the aeroplane look attractive \color{black}

d. To increase the speed of the aeroplane \color{black}

91 / 100

Category: Fluid friction depends on speed, shape, and nature of the fluid

91. (A) The shape of an aeroplane is designed to reduce fluid friction.
(R) Special shapes help in minimising the energy lost due to fluid friction.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

92 / 100

Category: Fluid friction depends on speed, shape, and nature of the fluid

92. (A) The drag force on an object moving through a fluid is independent of the object’s speed.
(R) The shape of the object and the nature of the fluid are the only factors that determine the drag force.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

93 / 100

Category: Drag: The frictional force in fluids

93. Which of the following factors does NOT directly affect the drag force experienced by an object moving through a fluid?

a. Speed of the object

b. Shape of the object \color{red}

c. Color of the object

d. Nature of the fluid

94 / 100

Category: Drag: The frictional force in fluids

94. (A) The drag force experienced by an object moving through a fluid can be minimized by shaping the object similarly to a bird or fish.
(R) Birds and fishes have evolved to have streamlined shapes that reduce energy loss due to fluid friction.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

95 / 100

Category: Importance of streamlining shapes:

95. What is the frictional force exerted by fluids on objects moving through them called?

a. Gravity

b. Inertia

c. Drag

d. Buoyancy

96 / 100

Category: Importance of streamlining shapes:

96. Which factor does NOT directly influence the drag force on an object moving through a fluid?

a. Speed of the object relative to the fluid

b. Shape of the object

c. Nature of the fluid

d. Material of the object

97 / 100

Category: Birds and fish have special body shapes

97. (A) Birds and fish have evolved streamlined body shapes to minimize energy loss due to fluid friction.
(R) The streamlined shape reduces the drag force acting on them by decreasing the surface area in contact with the fluid.

a. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

b. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

c. Assertion is true, but Reason is false.

d. Assertion is false, but Reason is true.

98 / 100

Category: Birds and fish have special body shapes

98. Which of the following shapes is most likely to reduce fluid friction?

a. Circular

b. Triangular

c. Streamlined

d. Rectangular

99 / 100

Category: Aeroplanes and vehicles are designed to minimize fluid friction

99. Which of the following factors does NOT affect the drag force experienced by an object moving through a fluid?

a. Speed of the object

b. Shape of the object \color\ Nature of the fluid

c. Color of the object

100 / 100

Category: Aeroplanes and vehicles are designed to minimize fluid friction

100. Which of the following shapes would likely experience the least fluid friction when moving through air?

a. Spherical

b. Teardrop

c. Cube

d. Cylinder

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