Chapter 12 Friction mcqs & important questions science | class 8th

MCQ Questions for Class 8 Science: Ch 12 Friction

1. Which of the following produces least friction?

(a) Sliding friction

(b) Rolling friction

(c) Composite friction

(d) Static friction

► (b) Rolling friction

2. In machine, friction between moving parts is reduced by

(a) Heating machine

(b) Using powder

(c) Using lubricants

(d) Using paints

► (c) Using lubricants

3. Why is a carrom board usually powdered before playing?

(a) For increasing friction

(b) For decreasing friction

(c) For decoration

(d) For fragrance

► (b) For decreasing friction

4. Thermos flask keeps hot liquid hot and cold liquid cold by

(a) Heating

(b) Friction

(c) Preventing heat loss

(d) Cooling

► (c) Preventing heat loss

5. Substances are called lubricants which are used to

(a) increase friction

(b) decrease friction

(c) increase or decrease friction

(d) none of these

► (b) decrease friction

6. Which force prevents us from slipping while walking on the road?

(a) Muscular force of our body

(b) Gravitational pull by the earth

(c) Frictional force

(d) Balanced forces of nature

► (c) Frictional force

7. Which of the following activities is easier to perform on a drum of 10 kg?

(a) Dragging the drum

(b) Lifting the drum

(c) Rolling the drum

(d) All of the above need the same effort

► (c) Rolling the drum

8. The substance which reduce friction are called

(a) Lubricants

(b) Wheels

(c) Powder

(d) Graphite

► (a) Lubricants

9. A toy car released with the same initial speed will travel farthest on

(a) Muddy surface

(b) Cemented surface

(c) Brick surface

(d) Polished marble surface

► (d) Polished marble surface

10. Which of the following materials is likely to have the least friction?

(a) Wood

(b) Cardboard

(c) Glass

(d) Paper

► (c) Glass

11. Friction is a __________

(a) Contact force       

(b) Non-contact force       

(c) Magnetic force       

(d) None of these

► (a) Contact force       

12. Fluids are

(a) gases

(b) liquids

(c) gases and liquids both

(d) none of these

► (c) gases and liquids both

13. In the decreasing order of magnitude, which of the following is correct?

(a) Rolling < static < sliding friction

(b) Static > sliding > rolling friction

(c) Static > rolling > sliding friction

(d) Sliding < static < rolling friction

► (b) Static > sliding > rolling friction

14. Which of the following statements is NOT true?

(a) Friction can be reduced by converting sliding friction into rolling friction.

(b) Friction in air and water can be reduced by streamlining the shape of the objects.

(c) A polished surface will have less friction.

(d) Friction can be reduced to zero.

► (d) Friction can be reduced to zero.

15. Striking a matchstick produces fire by

(a) Contact force

(b) Friction

(c) Chemical reaction

(d) Physical reaction

► (b) Friction

16. The shape of fish is streamlined to

(a) Change the direction

(b) Increase fluid friction

(c) Facilitate breathing

(d) Decrease fluid friction

► (d) Decrease fluid friction

17. Friction produces

(a) Motion

(b) Force

(c) Heat

(d) Light

► (c) Heat

18. Why are certain bodies streamlined?

(a) To increase friction

(b) To decrease weight

(c) To reduce friction

(d) To increase weight

► (c) To reduce friction

19. Carpenters often grease screws before fixing them to

(a) Decrease friction

(b) Increase friction

(c) Make it light weight

(d) All of the above

► (a) Decrease friction

20. Soapy water on floor would make it

(a) More clean

(b) Difficult to walk

(c) More hygienic

(d) Easier to walk

► (b) Difficult to walk

21. Brakes of vehicle is stopped by using brake that works on property of

(a) Pressure

(b) Acceleration

(c) Retardation

(d) Friction

► (d) Friction

22. Friction always

(a) helps the motion

(b) opposes the motion

(c) both of these

(d) none of these

► (b) opposes the motion

23. If a body moves on the sandy surface, its motion will

(a) Increase

(b) Decrease

(c) Neither increase nor decrease

(d) None of these

► (b) Decrease

24. Why are spikes provided in the shoes of athletes?

(a) As a decoration

(b) To increase friction

(c) To decrease friction

(d) To give shape

► (b) To increase friction

25. Which of the following will offer least friction to run a toy car?

(a) Wet marble

(b) Towel

(c) Dry marble

(d) News paper

► (a) Wet marble

Class 8 Science Chapter 12 Extra Questions and Answers Friction

Extra Questions for Class 8 Science Chapter 12 Friction with Answers Solutions

Friction Class 8 Extra Questions Very Short Answer Type

Question 1.
What is the force of friction?
Answer:
The force acting on a moving object equal and opposite to the direction of motion is called force of friction.

Question 2.
What is the cause of friction?
Answer:
The irregularities on the two surfaces in contact is the cause of friction.

Question 3.
What is the force responsible for wearing out of bicycles tyres?
Answer:
Frictional force

Question 4.
Is the friction same for all objects?
Answer:
No

Question 5.
Why are wheels of vehicles made circular?
Answer:
Rolling friction is less than sliding friction.

Question 6.
What is the direction of force of friction acting on a moving object?
Answer:
Opposite to the direction of moving objects.

Question 7.
Why do pieces of luggage fit with rollers?
Answer:
To reduce friction and to pull them easily.

Question 8.
Why does a matchstick catch fire when rubbed on the rough surface of the box?
Answer:
Due to friction between the stick and rough surface a matchstick catches fire.

Question 9.
What is the name of special shape given to objects moving in fluids?
Answer:
Streamlined

Question 10.
Give one example where ball bearings are used.
Answer:
Ceiling fan

Question 11.
Does friction depend on the nature of objects?
Answer:
Yes

Question 12.
What is the use of lubricants?
Answer:
They are used to reduce friction.

Question 13.
Which surface does produce more friction smooth or rough surface?
Answer:
Rough surface

Question 14.
Why is fine powder sprinkled on the carrom board?
Answer:
In order to reduce friction powder is sprinkled on carrom board.

Question 15.
Why is it difficult to walk on the wet marble floor?
Answer:
The wet marble floor has less friction. So it is difficult to move on it.

Question 16.
Why does the jar of a mixer become hot when it is run for few minutes?
Answer:
It becomes hot due to friction.

Question 17.
Name the types of friction.
Answer:

• Static friction
• Sliding friction
• Rolling friction
• Fluid friction

Question 18.
Which force helps us to write on the paper or blackboard?
Answer:
Frictional force

Question 19.
What is drag?
Answer:
The frictional force exerted by fluids is called drag.

Question 20.
What are fluids?
Answer:
Commonly gases and liquids are called fluids.

Question 21.
Give some examples having streamlined body.
Answer:
Aeroplanes, birds, ships, etc.

Question 22.
Oil, creams and grease are called lubricants. Why?
Answer:
Because they reduce friction.

Question 23.
How can fluid friction be minimised?
Answer:
By giving suitable shapes to bodies moving in fluids.

Question 24.
When does static friction come into play?
Answer:
When we try to move an object at rest, static friction comes into play.

Question 25.
Can we reduce friction to zero?
Answer:
No

Friction Class 8 Extra Questions Short Answer Type

Question 1.
If we push the book on the table, it stops after sometime. Why?
Answer:
When we push the book on a table, a force is applied on it in the opposite direction of the motion called force of friction. This force opposes the movement and the book stops.

Question 2.
Why are the worn-out tyres discarded?
Answer:
The worn out tyres are discarded because their tread are worn off and limiting their effectiveness of providing required amount of friction.

Question 3.
Why is it easier for the fish to swim in water?
Answer:
Fish can easily swim in water because it has a streamlined body which produces less friction. So it easily cuts through water and moves in it very easily.

Question 4.
Give some examples to show that friction produces heat.
Answer:
The examples are:

• Rubbing of our hands to keep us warm in winter.
• Rubbing of matchsticks on the rough surface to make fire.

Question 5.
Give some examples of smooth and rough surfaces.
Answer:
Smooth surfaces: Surface of the mirror, surface of wet soaps, glazed tiles, surface of an oily pot, etc.
Rough surfaces: Surface of plyboard, unpainted wall, brick, tyres, etc.

Question 6.
What is a spring balance?
Answer:
A spring balance is a device which measures the force acting on an object. It contains a coiled spring. When a force is applied on it, the spring gets stretched. The pointer moves on the scale showing the magnitude of the force.

Question 7.
How does the friction depend on the nature of the surface?
Answer:
Nature of the surface is one of the factors affecting friction. When we move on any surface, we apply a force to overcome the interlocking of the surfaces. Rough surfaces have a larger number of irregularities and greater frictional force.

Question 8.
What are the two factors on which the force of friction depends?
Answer:
These two factors are:

• The nature, i.e., smoothness or roughness of the surfaces in contact.
• How the surfaces in contact pressed together.

Question 9.
When the two surfaces are pressed harder, friction increases. Explain why?
Answer:
The friction is caused by the interlocking of irregularities in the two surfaces. It is obvious that the force of friction will increase if two surfaces are pressed harder. This can be experienced by dragging a mat when nobody is sitting on it and when a person is sitting on it.

Question 10.
What is a measure of static friction?
Answer:
The force required to overcome friction at an instant an object starts moving from rest is a measure of static friction.

Question 11.
What is a measure of sliding friction?
Answer:
The force required to keep the object moving with the same speed is a measure of sliding friction.

Question 12.
Why is it easier to move the box already in motion than to get it started?
or
The sliding friction is slightly smaller than the static friction. Explain why?
Answer:
When the box starts sliding, the contact points on its surface, do not get enough time to lock into the contact points on the floor. So, the sliding friction is slightly smaller than the static friction. Hence, it is somewhat easier to move the box already in motion than to get it started.

Question 13.
Why are the soles of shoes and tyres of vehicles grooved?
Answer:
The soles of shoes and tyres of vehicles like cars, trucks, etc., are grooved to provide better grip on the floor or roads to move safely because grooving increases friction.

Question 14.
We use ball bearings between the hub and axle of ceiling fan and bicycles. Why?
Answer:
The rolling friction is smaller than the sliding friction. In most machines, sliding is replaced by rolling by using ball bearings to reduce friction. This is why ball bearings are used between the hub and axle of ceiling fan and bicycle.

Question 15.
Why are lubricants applied between the moving part of a machine?
Answer:
When lubricants are applied between the moving part of a machine, a thin layer is formed there and moving surfaces do not directly rub against each other. Interlocking of irregularities is avoided to a great extent and the movement becomes smooth.

Question 16.
How brake stop moving bicycles and automobiles?
Answer:
When we press the brake lever, the brake pads arrest the motion of the rim due to friction and the wheel stops moving. This is how brake stops moving bicycles and automobiles.

Question 17.
People often rub their hands in winter. Why?
Answer:
Friction produces heat. When we rub our hands together, the friction arises between them and heat is produced. This makes our hands warm. This is why people often rub their hands in winter.

Question 18.
Which factors affect fluid friction?
Answer:
The speed of the object with respect to the fluid, shape of the object and nature of the fluid affect fluid friction.

Question 19.
In some cases, we deliberately increase friction. Explain why?
Answer:
We need to increase friction in some cases like grooving in the sole of shoes, the treaded tyres of cars, trucks or other vehicles, using brake pads in the brake system of bicycles and automobiles. If we do not do so, we may slip on the floor or roads, vehicles may slip on the roads and they will not stop, our bicycles and automobiles will not stop, etc.