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Friction (Class - VIII)

Description: Friction
Number of Questions: 15
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Tags: Friction Class VIII Physics Factors Affecting Friction Harmful Affects of Friction Rolling Identities and Application Identities and their Applications Factorisation by Splitting Middle Term Factorization by Splitting Middle Term Preference for Rolling Friction Against Sliding Friction Harmful Effects of Friction How Smoothness Between Surfaces Affects Friction Decreasing Friction by Using Lubricants Decreasing Friction by Decreasing Roughness
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If a heavy suitcase is fitted with rollers, then it can be pulled very easily. It is because rollers convert

  1. sliding friction into rolling friction

  2. rolling friction into sliding friction

  3. static friction into sliding friction

  4. rolling friction into static friction

  5. sliding friction into static friction

Show answer
Correct Option: A
Explanation:

This is the correct option. If a heavy suitcase is fitted with rollers, then it can be pulled very easily. It is because rollers convert sliding friction into rolling friction.

Frictional force always opposes the motion of one object over another object. On which of the following factors does the friction between two surfaces depend?

a. The amount of surface area of the two objects that is in contact with each other b. Smoothness or roughness of the two surfaces c. The force with which the two surfaces are pressed together

  1. Only a

  2. Only b

  3. Only a and b

  4. Only b and c

  5. Only a and c

Show answer
Correct Option: D
Explanation:

This is the correct option. The friction between two surfaces depends on the smoothness or roughness of the two surfaces and the force with which the two surfaces are pressed together.

Arrange the following types of forces in increasing order of their magnitudes:

a. Sliding friction b. Rolling friction c. Static friction

  1. Static friction, rolling friction, sliding friction

  2. Sliding friction, static friction, rolling friction

  3. Rolling friction, sliding friction, static friction

  4. Static friction, sliding friction, rolling friction

  5. Rolling friction, static friction, sliding friction

Show answer
Correct Option: C
Explanation:

This is the correct option. Rolling friction is much less than sliding friction. Sliding friction is less than static friction. Thus, the correct increasing order of the forces will be: Rolling friction, sliding friction, static friction.

Which of the following statements is/are false?

a. The interlocking of irregularities on the two surfaces opposes the motion of one object over another and gives rise to force of friction. b. Sliding friction comes into play when an object is moving over another object. c. The more the roughness of a surface, the larger is the number of irregularities on its surface and hence, the lesser will be the friction.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c

Show answer
Correct Option: E
Explanation:

This is the correct option as this statement is false. The more the roughness of a surface, the larger is the number of irregularities on its surface and hence, the greater will be the friction.

Friction helps in performing many daily life activities. Which of the following is not an advantage of friction?

  1. It enables us to cut wood with a saw.

  2. It enables us to light a matchstick.

  3. It enables us to pick and hold things in our hands.

  4. It enables rubber brake pads to be rubbed off.

  5. It enables us to write and draw on paper.

Show answer
Correct Option: D
Explanation:

This is the correct option as this is not an advantage of friction. It causes rubber brake pads to be rubbed off. They gradually get worn and are then needed to be replaced.

Which of the following statements is/are false?

a. Ball bearing is a device that usually converts rolling friction into sliding friction. b. A body shape that offers very little resistance to the flow of air or water around it is called streamlined shape. c. Drag is the frictional force that is exerted by a fluid.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c

Show answer
Correct Option: A
Explanation:

This is the correct option as this statement is false. Ball bearing is a device that usually converts sliding friction into rolling friction.

Maximum friction will be produced in which of the following cases?

  1. Rubbing of sand paper on a polished ceramic tile

  2. Rubbing of sand paper on polished marble flooring

  3. Rubbing of sand paper on glass table top

  4. Rubbing of sand paper on iron sheet

  5. Rubbing of sand paper on sand paper

Show answer
Correct Option: E
Explanation:

This is the correct option. Maximum friction will be produced by rubbing of sand paper on sand paper.

Lubricants are the substances that reduce friction. Which of the following lubricants can be used to reduce friction on a carrom board?

  1. Oil

  2. Fine powder

  3. Grease

  4. Graphite

  5. Ball bearing

Show answer
Correct Option: B
Explanation:

Fine powder can be used to reduce friction on a carrom board.

Which of the following statements is false?

  1. Aeroplanes are designed in such a way so that they can increase fluid friction.

  2. The larger the size of an object moving through a fluid, the greater will be the drag acting on it.

  3. The objects having streamlined shapes face much less drag when moving through a fluid than the objects which do not have streamlined shapes.

  4. The lower the speed of an object moving through a fluid, the lesser will be the drag acting on it.

  5. When objects move through fluids, they lose energy in overcoming friction.

Show answer
Correct Option: A
Explanation:

This is the correct option as this statement is false. Vehicles are designed to have shapes that reduce fluid friction.

Which of the following statements is/are false?

a. Friction always opposes motion between the surfaces in contact with each other. b. Drag force acts in a direction opposite to the direction of motion of the object. c. Fluid friction increases the speed of objects moving through the fluids.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c

Show answer
Correct Option: E
Explanation:

This is the correct option as this statement is false. Fluid friction reduces the speed of objects moving through the fluids.

Which of the following is not a method of increasing friction?

  1. It can be increased by making grooves in shoe soles.

  2. It can be increased by making treads in tyres of vehicles.

  3. It can be increased by making the surfaces smooth.

  4. It can be increased by providing spikes in shoes of players and athletes.

  5. It can be increased by the use of some coarse substance on the hands of gymnasts.

Show answer
Correct Option: C
Explanation:

This is the correct option as this is not a method to increase friction. Friction can be reduced by making the surfaces smooth by polishing.

A person is walking towards the west direction. The force of friction due to ground will act in which of the following directions?

  1. West

  2. East

  3. South

  4. North

  5. None of these

Show answer
Correct Option: B
Explanation:

This is the correct option. As the force of friction acts in the opposite direction to the direction of movement, so the force of friction due to ground will act in the east direction.

Static friction between a big box and a small box is measured to be 100 N. Which of the following will be the sliding friction between these two boxes?

  1. 90 N

  2. 110 N

  3. 120 N

  4. 130 N

  5. 150 N

Show answer
Correct Option: A
Explanation:

This is the correct answer. 90 N will be the measure of sliding friction between the two boxes as sliding friction is always lesser than the static friction.

Which of the following statements is/are false?

a. Friction can be reduced, but it can never be made zero. b. A teacher is able to write on the blackboard with a chalk due to friction between the blackboard and the chalk. c. Static friction comes into play when one tries to stop a moving object.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c

Show answer
Correct Option: E
Explanation:

This is the correct option as this statement is false. Static friction comes into play when one tries to move a stationary object.

Which of the following objects will be the most difficult for a person to hold in his hands if he applies some mustard oil on his hands?

  1. An earthen cup

  2. A glass tumbler

  3. A thermocol tumbler

  4. A wooden cup

  5. None of the above

Show answer
Correct Option: B
Explanation:

This is the correct option. A glass tumbler will be the most difficult for the person to hold because the oil on the outer surface of the glass tumbler reduces the friction between the glass tumbler and his hands.

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