Living Science Solutions for Class 8 Science Chapter 12 Friction are provided here with simple step-by-step explanations. These solutions for Friction are extremely popular among class 8 students for Science Friction Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Living Science Book of class 8 Science Chapter 12 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Living Science Solutions. All Living Science Solutions for class 8 Science are prepared by experts and are 100% accurate.

Page No 155:

Question 1:

Friction is
(a) always a disadvantage.
(b) always an advantage.
(c) sometimes a disadvantage and sometimes an advantage.
(d) neither a disadvantage nor an advantage.

Answer:

 (c) sometimes a disadvantage and sometimes an advantage
Friction is sometimes a disadvantage and sometimes an advantage.

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Question 2:

It is difficult to walk on ice because
(a) pressure is high.
(b) pressure is low.
(c) friction is high.
(d) friction is low.

Answer:

 (d) friction is low
Ice offers less friction.

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Question 3:

Friction can be increased by
(a) making the surfaces smooth.
(b) lubricating the surfaces.
(c) using ball bearings.
(d) making the surfaces rough.

Answer:

 (d) making the surfaces rough

Friction increases with roughness.

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Question 4:

Which of these is true about friction?
(a) It can stop a moving object.
(b) It can change the shape of an object.
(c) It can change the direction of a moving object.
(d) It can make a moving object move faster.

Answer:

 (a) It can stop a moving object.
Friction acts as a decelerating force against motion; it helps in slowing down a body, thereby eventually bringing it to rest.

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Question 5:

In which case is friction a disadvantage?
(a) running a machine
(b) walking
(c) applying brakes
(d) writing

Answer:

 (a) Running a machine

While running a machine, energy is lost because of friction. Hence, in this case, friction is a disadvantage.

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Question 6:

Ball bearings are useful because
(a) rolling friction is more than sliding friction.
(b) rolling friction is less than siliding friction.
(c) rolling friction is same as sliding friction.
(d) it is easier to apply grease to ball bearings to reduce friction.

Answer:

 (b) rolling friction is less than sliding friction

Rolling friction is less than sliding friction because of the minimal surface of contact between two bodies.

Page No 155:

Question 1:

Friction always opposes __________

Answer:

Friction always opposes the motion of a body.

Page No 155:

Question 2:

Friction is caused by __________ on the surfaces in contact.

Answer:

Friction is caused by irregularities on the surfaces in contact.

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Question 3:

Is friction a contact or a non-contact force?

Answer:

Friction is a contact force, i.e., it requires two bodies to be in contact.

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Question 4:

The smoother a surface is, the __________ (greater/lesser) will be the friction.

Answer:

 lesser  

Frictional force decreases with the decrease in the roughness of the surfaces in contact.

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Question 5:

Brakes on cars will work best if the friction between the brake shoes and wheels is reduced. True or false?

Answer:

False. Frictional force helps in reducing the motion of a body. More the friction, more the opposing force and faster the stoppage of the car.



Page No 156:

Question 1:

Discuss three situations in daily life where friction is an advantage?

Answer:

Three situations in daily life where friction is an advantage:
1) Walking - Friction is required between the feet/footwear and the ground to prevents slips.
2) Mechanical Brakes - Mechanical brakes help in slowing down the motion of a machine whenever desired. For example, friction is required to bring a car to rest.
3) Matchbox - Friction between the match stick and the matchbox helps in generating heat; this heat helps in lighting the matchstick.

Page No 156:

Question 2:

Explain with examples the disadvantages of friction.

Answer:

Friction reduces the relative motion between two objects in contact. It is a disadvantage in many situations. Let us take the example of the mechanical engine used in cars. Friction between the mechanical components of the engine prevents smooth movements. This causes loss of energy in the form of heat, sound, etc. This reduces the efficiency of the car. If the engine is not properly lubricated, excessive friction may even damage its mechanical parts because of excess heat production. The excess sound coming out of the engine is also undesirable.

Page No 156:

Question 3:

Explain four methods by which friction between two solid surfaces in contact can be reduced.

Answer:

Following are the methods by which friction between two solid surfaces in contact can be reduced:
1) Lubrication - It helps in reducing roughness, which decreases friction.
2) Ball Bearings - Since rolling friction is less than sliding friction, ball bearings help in maintaining minimal surface of contact between two surfaces in motion.
3) Polishing - Smooth surfaces or bearings work better than the rough ones.
4) Streamline Design - A streamlined design prevents friction due to fluids.

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Question 6:

Friction causes wastage of energy. True or false?

Answer:

True. Friction causes loss of energy in the form of heat, sound, light, etc.

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Question 7:

A machine with moving parts will become less hot while running if it is well lubricated. True or false?

Answer:

True
Friction causes loss of energy in the form of heat. When a machine is well lubricated, friction is reduced; therefore, less heat is produced.

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Question 8:

Friction due to fluids is called __________

Answer:

Friction due to fluids is called drag.

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Question 9:

Rolling friction is __________ (greater/smaller) than sliding friction.

Answer:

 Rolling friction is smaller than sliding friction.

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Question 10:

To reduce fluid friction, the object should have a __________ shape.

Answer:

 To reduce fluid friction, the object should have a streamlined shape.

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Question 1:

If there was no friction, what would happen to a moving object?

Answer:

Friction affects the relative motion between two surfaces in contact. Without friction, objects would not be able to move from a stationary position or stop when in motion. When a body is in motion and if there is no friction, it becomes impossible to bring it to rest. Think of a situation when you are travelling in a car and you cannot stop it because there is no friction between the surface of the tyres and that of the road. It will be a disadvantage in this case.

Page No 156:

Question 2:

When you rub your hands together, they become warm. What is this due to?

Answer:

Friction between the surfaces of hands produces heat, which makes them warm when rubbed together. When you rub your hands together, it causes friction. This leads to the production of heat, which makes your hands warm. This is because of the roughness of the surfaces of hands. It is a classic example of the conversion of mechanical energy to heat energy.

Page No 156:

Question 3:

If you try to hold a glass with oil on your hands, it tends to slip. Why?

Answer:

Friction between two surfaces in contact is reduced when the surfaces are lubricated. Oil is a lubricating agent. Hence, when you try holding a glass with oil on your hands, it tends to slip.

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Question 4:

Why do you think rolling friction is less than sliding friction?

Answer:

Rolling friction is less than sliding friction because of the minimal surface of contact between two surfaces. For a rolling body, the contact surface area is less and goes on changing. In case of rolling friction, we can assume that a point of a body is in contact with a surface; while in case of sliding friction, the whole surface area of the body is in contact with the surface.

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Question 5:

Friction is a necessary evil. Explain.

Answer:

Friction affects the relative motion between two bodies in contact. Without friction, objects cannot move from a stationary position or stop when in motion. Suppose you are walking on the road and encounter a smooth surface. You will fall because there will be no friction to hold your feet firmly on the surface. Now, let us change the situation. Let us suppose you are standing on a smooth surface and you are asked to walk on that surface. Again, you will not be able to walk properly because of lack of friction. Hence, friction is a necessary evil.

Page No 156:

Question 1:

What is friction?

Answer:

 Friction is a force that resists the relative motion between two surfaces in contact. It is a contact force.

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Question 2:

An object is moving from north to south. What is the direction of the force of friction on the object?

Answer:

Frictional force acts in the direction opposite to the direction of motion of a body. Because the object is moving from north to south, the direction of frictional force is from south to north.

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Question 3:

On what principle do ball bearings work?

Answer:

A ball bearing works on the principle that rolling friction is less than sliding friction. It helps in reducing friction between two surfaces in contact and maintaining separation between the bearing races, thereby allowing minimal surface contact between two surfaces.

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Question 4:

How does lubrication reduce friction?

Answer:

Lubrication helps in reducing roughness between two surfaces in contact. Thus, friction decreases with the reduction in the roughness between two surfaces. 

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Question 5:

Give an example to show the effect of heat generated in a machine due to excessive friction.

Answer:

Friction opposes the relative motion between two surfaces in contact. The loss of energy occurs in the form of heat, sound, light, etc. For example, mechanical engines are lubricated time to time to reduce excessive friction that prevents the loss of energy in the form of heat. Take example of a car, motorbike or bicycle whose mechanical parts are lubricated to reduce excessive friction.

Page No 156:

Question 1:

What is the effect of friction on motion?

Answer:

Friction is a force that reduces the relative motion between two surfaces in contact. It helps in reducing the motion of a body and to slow down the body till it stops.

Page No 156:

Question 2:

What causes friction between two surfaces in contact?

Answer:

The roughness of surfaces causes friction between two surfaces in contact. To ordinary eyes, the surfaces may seem smooth, but at a microscopic level, the surfaces have crest and trough. Under magnification, they look a little like mountain ranges, full of peaks and valleys. Hence, when two surfaces come in contact, the motion between them is reduced because of the crest and trough on the surfaces.

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Question 3:

Why does a rough surface have greater friction than a smooth surface?

Answer:

Rough surfaces have greater friction than smooth surfaces. Rough surfaces have grooves on them. When two rough surfaces are in contact, the grooves of one go inside the grooves of the other, thus making the movement difficult. Hence, roughness increases friction.

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Question 4:

Give two situations where it is desirable to increase friction.

Answer:

Two situations where it is desirable to increase friction:
1) Walking - Friction is required between feet/footwear and the ground to prevent slips.
2) Machine Brakes - Friction is desirable in brakes to reduce motion in a quick time.

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Question 5:

What is 'streamlining'? How is it useful?

Answer:

Streamlining is a phenomenon through which objects are designed in such a way that a fluid passes easily over them with least resistance. Take the example of cars. They have a streamlined shape to allow the air to flow around them easily with least resistance; without this streamlining, the air resistance would be much greater.



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