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# NCERT Solutions for Class 8 Science Chapter 12: Friction

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NCERT solutions for class 8 Science Chapter 12 Friction is one of the most crucial resources for the students of 8th standard. The solutions aids to help students understand the chapter in an interesting way. These solutions of Chapter 12 friction are created by experts of subject according to the latest CBSE guidelines and syllabus (2019-20).

NCERT Solutions for Class 8 Science Chapter 12 by Swiflearn are by far the best and most reliable NCERT Solutions that you can find on the internet. These NCERT Solutions for Class 8 Science Chapter 12 are designed as per the CBSE Class 8 Science Syllabus. These NCERT Solutions will surely make your learning convenient & fun. Students can also Download FREE PDF of NCERT Solutions Class 8 Chapter 12.

## NCERT Solutions for Class 8 Science Chapter 12: Friction

#### 1. Fill in the blanks.(a) Friction opposes the _____________ between the surfaces in contact witheach other.(b) Friction depends on the _____________ of surfaces.(c) Friction produces __________.(d) Sprinkling of powder on the carrom board ________ friction.(e) Sliding friction is ___________ than the static friction.

Solution:
(a) Friction opposes the motion between the surfaces in contact with each other.
(b) Friction depends on the nature of surfaces.
(c) Friction produces heat.
(d) Sprinkling of powder on the carrom board reduces friction.
(e) Sliding friction is less than the static friction.

#### 2. Four children were asked to arrange forces due to rolling, static and slidingfrictions in a decreasing order. Their arrangements are given below. Choosethe correct arrangement.(a) rolling, static, sliding(b) rolling, sliding, static(c) static, sliding, rolling(d) sliding, static, rolling

Solution:
Option (c) is the correct answer because when an object is already in motion (sliding), the irregularities on its surface do not get enough time to lock into the irregularities on the surface of the other object completely. Thus, sliding friction is smaller than the static friction. It is always easier to roll an object than to slide it over another object. Therefore, rolling friction is much less than sliding friction.

#### 3.Alida runs her toy car on dry marble floor, wet marble floor, newspaper and towel spread on the floor. The force of friction acting on the car on different surfaces in increasing order will be(a) wet marble floor, dry marble floor, newspaper and towel.(b) newspaper, towel, dry marble floor, wet marble floor.(c) towel, newspaper, dry marble floor, wet marble floor.(d) wet marble floor, dry marble floor, towel, newspaper.

Solution:

Option (a) is the correct option because the force of friction is more on a rough surface.

#### 4. Suppose your writing desk is tilted a little. A book kept on it starts slidingdown. Show the direction of frictional force acting on it.

Solution:
The direction of frictional force on the book is opposite to the direction of its motion and acts inupward direction. The diagram given below represents the direction of frictional force acting on the book.

#### 5. You spill a bucket of soapy water on a marble floor accidently. Would itmake it easier or more difficult for you to walk on the floor? Why?

Solution:
It will be more difficult to walk on the wet floor. This is because the friction between our foot and the floor will become very less and we may also slip due to lack of friction.

#### 6. Explain why sportsmen use shoes with spikes.

Solution:
Spikes increase the friction between the shoes and the ground and provide a better grip while running. Spikes also avoid slipping while playing or running. This is the reason why sportsmen use shoes with spikes.

#### 7. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?

Solution:
Force of friction depends on the mass of the object. The interlocking of irregularities on the surfaces of box and floor becomes strong, when a heavy object is placed on the floor. This is because the two surfaces in contact are pressed harder. This means more force is required to
overcome the interlocking. Thus, Seema will have to apply a greater force to push the heavier box, as compared toIqbal who has to push a lighter box.

#### 8. Explain why sliding friction is less than static friction.

Solution:
When an object is already in motion (sliding), the irregularities on the surface do not get enough time to lock into the irregularities on the surface of the other object completely. As the interlocking of the two surfaces is less in case of a moving object, the sliding friction is less than the static friction.

#### 9. Give examples to show that friction is both a friend and a foe.

Solution:
Examples where friction acts as a friend are:
a) Friction enables us to walk.
b) Friction enables us to write.
c) Friction helps to reduce the speed or stop a moving vehicle.
Examples where friction acts as a foe are:
a) The tires and soles of shoes wear out because of friction.
b) Friction produces heat between different parts of the machines which in turn damages the machines.

#### 10. Explain why objects moving in fluids must have special shapes.

Solution:
An object experiences an opposing force as it moves through the fluid. This opposing force is known as the drag force. This opposing force depends on the shape of the body. The force of friction acting on the object moving through the fluid can be minimized by giving them a special shape. Hence, it becomes easier for the object to move through the fluid.