# Friction Class 8 Extra Questions and Answers Science Chapter 12

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## Class 8 Science Chapter 12 Extra Questions and Answers Friction

Extra Questions for Class 8 Science Chapter 9 Friction with Answers

### Friction Class 8 Extra Questions Very Short Answer Type

Question 1.
The given sentence is true or false:
Rolling friction is greater than sliding friction.
False

Question 2.
Rewrite the sentence by correcting the mistakes:
Friction is not caused by the rrregula- rities on the two surfaces in contact. Smooth surfaces also do not have large number of irregularities on them.
Friction is caused by the irregularities on the two surfaces in contact. Smooth surfaces don’t have large number of irregularities on them.

Question 3.
Does the distance covered by a moving body depend on the nature of the surface on which it moves?
Yes, it does. Smoother the surface, bigger is the distance covered.

Question 4.
Can you imagine being able to walk if there were no Auction at all?
No.

Question 5.
Is sliding friction less than static friction ?
Yes, sliding friction is slightly less than static friction.

Question 6.
Would it be possible to hold the glass at all if there is no. friction?
No.

Question 7.
Why cannot we write on a smooth blackboard with chalk?
Because there is not sufficient friction on the blackboard.

Question 8.
Is friction a friend or foe?
Friction is both a friend and a foe.

Question 9.
What energy can be produced by friction?
Friction can produce heat energy.

Question 10.
What happens when you strike a matchstick against the rough surface on the side of matchbox ?
The matchstick catches fire.

Question 11.
How can efficiency of machinery be increased?
By reducing friction, the efficiency of the machinery can be increased.

Question 12.
What is the substance which reduces friction called?
It is called a lubricant.

Question 13.
What does air cushion between the moving parts of the machine do?
It reduces friction.

Question 14.
Can we reduce friction to zero by polishing surfaces or using large amount of lubricants ?
No, friction cannot be reduced to zero by any ‘means.

### Friction Class 8 Extra Questions Short Answer Type 1

Question 1.
Name factors on which force of friction depends.
Factors on which frictional force depends are :

1. Nature of surface in contact.
2. Area of contact of the two surfaces.
3. Relative speed of the surfaces.

Question 2.
When a brick kept on a table is pulled by a string to which a spring balance is attached, what gives the measure of the force of friction?
When a brick kept on a table is pulled by a string attached to it and a spring balance is also attached with the string, then the reading on the spring balance gives the measure of the force of friction between the surface of the brick and the floor.

Question 3.
If a body is made to move on the sandy surface, what will happen to its motion?
As the frictional force produced by the sandy surface is greater, so the motion of the body will be slower.

Question 4.
What we have to do when we attempt to move any surface over other?
When we attempt to move any surface over other, we have to apply a force to overcome the frictional force prevailing in between the surfaces.

Question 5.
Why is there a greater force of friction when a rough surface is involved?
On rough surfaces, there are a large number of irregularities (bumps) which facilitates interlocking. So, the force of friction is greater if a rough surface is involved.

Question 6.
How is it possible to write with chalk on black- board?
When we write with a chalk on the blackboard, its rough surface rubs off some chalk particles due to friction. So, we can see the writing on the blackboard.

Question 7.
Why are treaded tyres used in automobiles like cars, trucks or bulldozers?
The treaded tyres of cars, trucks and bulldozers provide better grip with the ground, due to increased friction. That is why they are used.

Question 8.
Why do Kabaddi players rub their hands with the soil?
The Kabaddi players rub their hands with the soil to increase friction for a firm grip of their opponents.

Question 9.
What do gymnasts do to have a better grip?
The gymnasts apply some coarse substance on their hands to increase friction for better grip.

Question 10.
When a few drops of oil are poured on the hinges of a door, why does the door move smoothly?
When a few drops of oil are poured on the hinges of the door it moves smoothly because oil is one of the lubricants used to minimise or reduce friction.

Question 11.
Define the term lubricant. Where are they used?
The substances which reduce friction are called lubricants. That is why, they are used in the machine parts.

Question 12.
In some machines, use of oil or lubricant is not advisable. Why?
In some machines, it may not be advisable to use oil or lubricant because they uses air cushion in between the moving parts to reduce friction.

Question 13.
Why do attaches are fitted with rollers?
Attaches and other pieces of luggage are fitted with rollers, because they enable the puller to pull them easily as wheels and rollers reduce friction facilitating rolling friction.

Question 14.
Define rolling friction.
When one body rolls over the surface of another body, the resistance to its motion is called rolling friction.

Question 15.
Does air exert friction?
Although air is very light and thin, yet it exerts frictional force on objects moving through it.

Question 16.
Does water exert friction?
Yes, water and other liquids exert force of friction when objects move through them.

Question 17.
Define drag.
The frictional force exerted by fluids (gases and liquids) is called drag.

Question 18.
What are the factors affecting friction on an object in fluids?
Factors affecting friction on an object in fluids are:

1. Objects speed with respect to the fluid
2. Shape of the object.
3. Nature of the fluid.

### Friction Class 8 Extra Questions Short Answer Type 2

Question 1.
Give any two methods each to increase and decrease friction.
Methods to increase the friction:
(a) By making the surfaces rough.
(b) By removing the lubrication between the two surfaces.
(c) By changing the rolling friction to sliding friction.

Methods to decrease the friction:
(а) By making the surfaces smooth.
(b) By applying the lubrication between the two surfaces.
(c) By changing the sliding friction to rolling friction.

Question 2.
Following are some of the examples which shows that ‘friction is our friend and foe.’ Choose from the given examples which example is useful for us and which is not.
(а) It allows us to grip and catch any object.
(b) It causes wear and tear in objects.

Helps in writing.
It helps to minimise the speed or to stop any moving objects.
(a) Useful,
(b) Not useful,
(c) Useful,
(d) Useful.

Question 3.
What do you mean by lubricants? What is their use?
The substances which reduce friction are called lubricants. To increase efficiency, friction has to be reduced. This can be done by applying oil, grease or graphite in between the moving parts of a machine. Then its thin layer is formed there and moving surfaces do not directly rub against each other. In this way, interlocking of irregularities is avoided to a great extent and movement becomes smooth.

Question 4.
Site some examples when we prefer to reduce friction.
Some examples where we prefer to reduce friction are:
Item used Used on Used for
(i) Fine powder
Carrom board
For easy movement of sticker.

(ii) Lubricants and air cushion
Moving machine parts

Reduce heat production and hence increasing efficiency. Also decreasing wear-tear rate.
(iii) Ball bearings Machine moving parts
To convert sliding friction to rolling friction.

### Friction Class 8 Extra Questions Long Answer Type

Question 1.
What are the different types of friction? Arrange them in the increasing order of their magnitude.