“Friction” is Chapter 14 taken from the JKBOSE textbook of Science for students of Class 8th. In the previous post, I provided you with Questions and Answers for Chapter 13 Pollution of Air and Water. This post is about the Friction Chapter 14 Class 8 Question Answers. Before we move on to solutions you must have your basics clear. So, let me begin by giving you a brief overview of what you have studied in this chapter.
Friction Chapter 14 Class 8 Question Answers
Overview of Chapter
- HOW IS FRICTION CAUSED?
- LAWS OF LIMITING FRICTION.
- ROLLING FRICTION.
- FRICTION DUE TO LIQUIDS AND GASES (FLUID FRICTION)
- BENEFITS OF FORCE OF FRICTION.
- Disadvantages of friction.
- Friction is a necessary evil.
- Ways of reducing friction.
INTRODUCTION: The force which opposes the motion of one object over another object in contact with it is termed a frictional force. There are three types of friction:
- Static friction.
- Sliding Friction.
- Rolling Friction.
HOW IS FRICTION CAUSED? Friction is caused by the interlocking of irregularities in the surfaces of two objects which are in contact with each other. There are three essential definitions related to friction.
- Static friction: The force of friction which does not allow two bodies to slide upon one another is called static friction.
- Limiting Friction: It is a maximum static force of friction that comes into play when one just slides upon another body is called limiting friction.
- Dynamic or Sliding Friction: It is a force of friction acting between two bodies when they are sliding upon one another with a uniform speed.
LAWS OF LIMITING FRICTION: Following are the important laws of limiting friction:
- Limiting friction always opposes the motion of a body and acts in the direction opposite to the applied force.
- It depends upon the nature of surfaces in contact with each other.
- Limiting friction increases with an increase in the weight of the body and vice versa.
- Limiting friction is independent of the area of contact between two surfaces; provided the weight of the body and the nature of the surface do not change.
ROLLING FRICTION: The frictional force experienced by a body when it is made to move over bodies like a roller or wheels is called rolling friction.
FRICTION DUE TO LIQUIDS AND GASES (FLUID FRICTION): The substances which can flow easily are called fluids. They have no fixed shape. Liquids and gases are fluids. Whenever an object moves through a fluid. It is termed fluid friction. It is also called drag.
The fluid friction depends on the following four factors:
- Speed of object with respect to the fluid.
- The shape of the object.
- Size of the object.
- Nature (viscosity) of the fluid.
BENEFITS OF FORCE OF FRICTION. Here are some important advantages of friction;
- It enables us to walk on the ground without slipping.
- Friction enables us to fix a nail into the wall.
- It enables the car to move on the road without skidding.
- The brakes of a vehicle slow down its speed or stop it due to friction.
- We can light a matchstick due to friction.
- Friction helps us to write or draw anything on paper.
- It helps us to pick up or hold things in our hands.
6.1 Disadvantages of Friction.
- It wears away the soles of our shoes.
- The tyres of vehicles wear out due to the force of friction.
- Friction wears out rubbing parts of the machines.
- It produces heat which may damage machines.
- Friction reduces the efficiency of machines.
- It wears out the steps of staircases in buildings and foot over-bridges.
6.2 Friction as a necessary evil: Friction plays an important role in our life. It has both advantages as well as disadvantages and due to this reason, it is termed a necessary evil.
6.3 Ways of reducing friction.
- By the use of lubricants.
- Using soap solutions.
- By using fine powders.
- Polishing rough surfaces to change them into smooth surfaces.
- By streamlining the shape of objects
- By converting sliding friction into rolling friction.
Class 8 Science Chapter 14 Friction Questions
1. Answer the following questions:
(i) Why are the worn-out tyres discarded?
Ans. The worn-out tyres are discarded because they do not offer the required amount of friction needed for applying brakes on the vehicles. As a result, vehicles can slip on the road and cause serious accidents.
(ii) Why do carrom coins move faster on carrom board when dusted with talcum powder?
Ans. The surface of the carrom board offers friction to the movement of coins due to irregularities in it. When the carrom board is dusted with talcum powder the irregularities in the surface of the carrom board get filled with it, so the force of friction between the surfaces of the carrom board and coins gets reduced. As a result, coins move faster on the carrom board.
(iii) Why is the surface of the conveyor belt made rough?
Ans. The conveyor belt is used to turn wheels and pulleys in factories. The surface of the conveyor belt is made rough in order to increase friction so that it may not slip.
(iv) Why is the sewing machine often oiled?
Ans. The sewing machine is oiled to reduce the friction in its various parts so that it may move freely and easily.
(v) Why do new automobile tyres have deep grooves?
Ans. The new automobile tyres have deep grooves to provide the required amount of friction to the vehicle. It prevents slipping or skidding of wheels on the road.
(vi) Why does a ball rolling on the ground slows down?
Ans. The ball rolling on the ground slows down due force of friction applied by the ground on the ball.
(vii) Why are the boats and aeroplanes given special shapes?
Ans. The boats and aeroplanes are given a special shape called streamlined shape because it reduces the force of friction applied by water and air on them. It helps them to move easily and freely in water and air respectively.
(viii) Why do meteors burn on entering the atmosphere?
Ans. The meteors enter into the atmosphere at very high speed as a result friction of air increases their temperature enormously due to which they get burnt on entering into the atmosphere of the earth.
(ix) Why do painters use sandpapers in polishing doors?
Ans. Painters use sandpaper in polishing doors in order to remove the irregularities or rough projections on the surface and make it smooth so that they can move their brush freely on it.
(x) Why it is easier to tie a knot with cotton string as compared to silk string?
Ans. It is easier to tie a knot with a cotton string as compared to silk string because silk is smoother than cotton and hence offers less friction as compared to cotton.
- Fill in the blank spaces by choosing the words from the list given below:
List, movement, sliding, streamlined, static, opposite
(i) Friction always acts in the direction opposite to the direction of applied force.
(ii) Static friction is a self-adjusting friction.
(iii) Friction is very useful as it helps in the movement of the bodies.
(iv) The sliding friction is 10 times the rolling friction.
(v) The boats and aeroplanes are streamlined so as to reduce fluid friction.
- The statements given below are incorrect. Write the correct statements:
(i) Sliding friction is slightly more than limiting friction.
Ans. Sliding friction is slightly less than limiting friction.
(ii) The conveyor belts are made rough, in order to decrease friction.
Ans. The conveyor belts are made rough, in order to increase friction.
(iii) The friction between two surfaces decreases with an increase in the weight of the body.
Ans. The friction between two surfaces increases with an increase in the weight of the body.
(iv) The friction offered by the wheels is sliding friction.
Ans. The friction offered by the wheels is rolling friction.
(v) The friction increases with the increase in the area of contact of two surfaces.
Ans. The friction is independent of the area of contact between two surfaces.
That’s all about Friction Chapter 14 Class 8 Question Answers. Hope it has helped you a lot. Do share your views about this post in the comment section below.