0

Increasing and reducing friction - class-VIII

Description: increasing and reducing friction
Number of Questions: 22
Created by:
Tags: physics friction force force and motion force and pressure
Attempted 0/22 Correct 0 Score 0

The surface of the head of a match stick and sides of a match box are deliberately made rough to:

  1. increase friction

  2. decrease friction

  3. increase amount of heat

  4. decrease amount of heat


Correct Option: A
Explanation:

The rough surface will increase the friction and so the rough surface of match box and match stick will produce more friction which helps in firing the stick easily.  

Correct air pressure in our vehicle tyres help to reduce:

  1. static friction

  2. sliding friction

  3. rolling friction

  4. all of the above


Correct Option: C
Explanation:

Correct air pressure helps in reducing deformation of the tyre and also provide an air cushion to reduce rolling friction. 


Option C is correct.

Wheels reduce friction due to:

  1. more area of contact

  2. less area of contact

  3. size

  4. all of the above


Correct Option: B
Explanation:

The friction will be more for more area of contact. Since the wheels have less area of contact so the friction will be less for them. 

With increase of temperature, the frictional force acting between two surfaces increases.

  1. True

  2. False

  3. Ambiguous

  4. Data Insufficient


Correct Option: B
Explanation:

Friction decreases with increase in temperature.

Friction is minimised by using

  1. Wheels and balI bearings

  2. More number of tyres in a car

  3. Rough surfaces

  4. None of these


Correct Option: A
Explanation:

Answer is A.

Bearings reduce friction by providing smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers 'bear' the load, allowing the device to spin smoothly.
The concept behind a bearing is very simple. Things roll better than they slide. The wheels on our car are like big bearings. If we had something like skis instead of wheels, our car would be a lot more difficult to push down the road.
That is because when things slide, the friction between them causes a force that tends to slow them down. But if the two surfaces can roll over each other, the friction is greatly reduced.

powder sprinkled on a carrom board

  1. magnifies friction.

  2. reduces friction.

  3. removes friction.

  4. does not affect friction.


Correct Option: B
Explanation:

The carom board may sometimes be very rough. Sprinkling powder on a microscopic level, the powder particles offer rolling friction to the striker because of which the striker can be used for smooth and fast play.

The force of friction on a static body ________ , if It is on a rough surface then.

  1. is always zero

  2. may be gravity.

  3. may be zero

  4. both B & C


Correct Option: D
Explanation:

The force of friction f is always opposite the direction the object that is moving . If the object would move, then the direction of the force of friction f will be opposite the movement. If the object would not move when there is no friction, then the force of friction is zero.Hence, though the surfaces of the object are rough the force of friction can be zero if the object would not move.

Powder is used in carrom board for

  1. Increasing friction

  2. Decreasing friction

  3. Decoration

  4. Fragrance


Correct Option: B
Explanation:

Answer is B.

The surface well powdered to stay away from harm to board surface due to scratch.It reduces the friction and helps in smoothing of the board and thereby allows the carom coins to go through in that flow which helps in fast play.
Powder is used in carom board for decreasing friction.

Friction depends upon ................. of surfaces.

  1. mass.

  2. nature of body.

  3. both A & B

  4. none


Correct Option: C
Explanation:

Friction depends upon mass and nature of the body of surfaces.
Friction depends partly on the smoothness of the contacting surfaces, a greater force being needed to move two surfaces past one another if they are rough than if they are smooth. However, friction decreases with smoothness only to a degree; friction actually increases between two extremely smooth surfaces because of increased attractive electrostatic forces between their atoms. 
Friction does not depend on the amount of surface area in contact between the moving bodies or (within certain limits) on the relative speed of the bodies. It does, however, depend on the magnitude of the forces holding the bodies together. 
When a body is moving over a horizontal surface, it presses down against the surface with a force equal to its weight, i.e., to the pull of gravity upon it; an increase in the weight of the body causes an increase in the amount of resistance offered to the relative motion of all the surfaces in contact.

Graphite powder is used in machines to _________.

  1. enhance friction

  2. enhance profit

  3. reduce friction

  4. reduce efficiency


Correct Option: C
Explanation:

Graphite powder is used in machines to reduce friction
Graphite is the only non-metal element that is a good conductor of electricity. Crystal structures rarely occur and easily break down. This is the reason for the material's greasy feeling despite being a dry lubricant.

Can friction ever be eliminated?

  1. Yes

  2. No

  3. Sometimes

  4. Depends on the object in regard


Correct Option: B
Explanation:

However smooth or polished a surface might be, it always has some irregularities. Thus, the friction can never be eliminated.

The substance that helps to ______ friction are called lubricants.

  1. increase

  2. decrease

  3. create

  4. eliminate


Correct Option: B
Explanation:

Oils, grease, graphite, etc., are examples of lubricants. These form a thin layer between the two surfaces in contact thus avoiding them from scrubbing directly against each other. This makes the movement smooth and reduces friction.

Why are the tyres of automobiles grooved?

  1. To improve the design

  2. To increase friction

  3. To make it durable

  4. To make it strong


Correct Option: B
Explanation:

If the tyres of automobiles were smooth, the friction produced would be minimal and thus, it would be difficult to stop or turn the automobile, increasing the risk of accidents. Hence, the tyres are grooved so as to increase the friction between the tyre and the surface of the road.

Kabaddi players rub their hands with soil so that they can :

  1. make their skin dry

  2. moisture the hands

  3. get a better grip while holding the opponent

  4. soil the opponent


Correct Option: C
Explanation:

By rubbing their hands with soil, they make their hands rough. A rough surface has more friction which enhances their grip while holding the opponent.

Which of the following are done to reduce friction?
a) Making grooves in the shoes
b) Polishing rough surfaces
c) Using wheels, ball bearings
d) Creating an air cushion

  1. a, b and c

  2. c and d

  3. b, c and d

  4. All of the above


Correct Option: C
Explanation:
Making grooves in the shoes increases friction.
Polishing rough surfaces makes it smooth, thus reducing friction. 
Wheels and ball bearings create rolling friction which has the least magnitude compared to sliding and static friction.
Air cushion makes a layer of air between two surfaces, which helps in reducing friction.

How do brake pads help in stopping an automobile?

  1. Brake pads press on the wheel and increase friction.

  2. Due to braking, the air pressure increases and the wheels stop.

  3. Both A and B

  4. None of the above


Correct Option: A
Explanation:

The brake pads press on the wheels and increase the friction since the surface of the brake pads and the wheels are irregular, and the rough surface increases friction that opposes the motion of the wheel.

Which of the following are done to increase friction?

  1. Greasing the machines

  2. Treading the tyres

  3. Sprinkling powder on the carom board

  4. All of the above


Correct Option: B
Explanation:

The tyres are treaded to make it rough so that the frictional force increases when it comes in contact with the road. 

All others are done to decrease friction.

The steps for decreasing friction includes:

  1. ball bearing used in moving parts of a machine

  2. the streamlined shape of an aircraft

  3. the layer of air between the hull of a hovecraft

  4. none of these


Correct Option: A,B,C
Explanation:

1) As rolling friction is less than sliding friction the shafts are fixed on ball bearing so that so that friction is reduced considerably.

2) The friction due to air is reduced by making the automobiles streamlined. Streamline shape allows more air and water to flow easily which offers least resistance.
3) Another way of reducing friction is to separate surfaces by air. This principle is used in hovecraft. The layer of air reduces friction allowing aircraft to move easily.

If we apply oil on door hinges, the friction will:

  1. increase

  2. decrease

  3. disappear altogether

  4. will remain unchanged


Correct Option: B
Explanation:

Lubrication always decreases friction between two surfaces. Hence putting oil will decrease friction.

In a large commercial complex there are four ways to reach the main road. One of the path has loose soil, the second is laid with polished marble, the third is laid with bricks and the fourth has gravel surface. It is raining heavily and Paheli wishes to reach the main road. The path on which she is least likely to slip is:

  1. loose soil

  2. polished marble

  3. bricks

  4. gravel surface


Correct Option: A
Explanation:

Loose soil will provide the maximum friction and hence less chances of slipping.

Which of the following is used to reduce friction :
1. Streamlines
2. Use of ball bearings
3. Lubrication

  1. 1 & 2 only

  2. 1 & 3 only

  3. 2 & 3 only

  4. 1, 2 & 3


Correct Option: D
Explanation:

All the mentioned option are correct.

Streamlines reduces the friction in fluid.
Use of ball bearing reduces the friction in machines rotating parts.
Lubricants are used in machines  and moving parts to reduce friction.

Option D is correct.

Why are efforts made to reduce friction?

  1. Energy is lost in overcoming friction.

  2. Overcoming friction is a time consuming process.

  3. Both A and B

  4. None of the above


Correct Option: A
Explanation:

A lot of the applied energy is lost in overcoming friction so as to put a body in motion.Hence efforts are made to reduce friction.

- Hide questions