NCERT Solutions for Class 8 Science Chapter 12 Friction

Friction is defined as the force that resists motion. It is a very important force. It helps us to gain control over many day to day activities like walking, running, driving and even writing. If you are wondering how then you will understand better on going through this chapter.

This chapter from class 8 science NCERT solutions will elaborate upon Friction and how it is important for many of our activities. Students will learn about the causes and effects of friction.

Download PDF of NCERT Solutions for Class 8 Science Chapter 12 Friction

Question: 1. Fill in the blanks:

(a) Friction opposes the _____________ between the surfaces in contact with each other.

Friction resists the motion between two surfaces that are in touch.

(b) Friction depends on the _____________ of surfaces.

The nature of surfaces in contact determines the friction between them.

(c) Friction produces __________.

When we rub our hands, they become warm due to friction. So, friction generates heat.

(d) Sprinkling of powder on the carrom board ________ friction.

To reduce friction, the powder is put on the carrom board.

(e) Sliding friction is ___________ than the static friction.

Answer: As sliding friction is less than static friction, pushing a heavy object in motion is easier than pushing the same object at rest.

Let's understand the basics of non contact force, and learn what is frictional force?

Question: 2. Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below.

Choose the correct arrangement.

(a) Rolling, static, sliding

(b) Rolling, sliding, static

(c) Static, sliding, rolling

(d) Sliding, static, rolling

Answer: Sliding friction is less than static friction. Rolling friction is the smallest. So, the right order is:

Static friction > Sliding friction > Rolling friction

Question: 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

Answer: Friction is determined by the nature of the surfaces in contact, the towel, which has a rough surface, will provide the most friction. Although the surface of the newspaper is not very smooth, it has less friction than a towel. A dry marble floor is a smooth surface, it will have less friction, but when the marble floor is wet, the friction decreases even more. As a result, the right order is:

Wet marble floor, dry marble floor, newspaper, and towel.

Question: 4. Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.

Answer: If the book is sliding down the table, the direction of friction will be opposite to the motion of the book.

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NCERT Solutions for Class 8 Maths

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

Answer: When soapy water is splashed on a marble floor, the amount of friction is greatly decreased, making walking on the floor extremely difficult.

Question: 6. Explain why sportsmen use shoes with spikes.

Answer: The friction between the shoes and the ground is increased by spikes. As a result, athletes have a better hold on the ground. They are capable of running without slipping.

Question: 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?

Answer: Seema has to use more force to move the heavy box because friction between the heavy box and the floor is greater.

Question: 8. Explain why the sliding friction is less than the static friction.

Answer: There are irregularities on all the surfaces. When two surfaces come in contact, their irregularities lock into each other, preventing the motion of surfaces in contact. So, we push the object to break the interlocking. When we apply enough force, the surface starts sliding and the interlockings do not get enough time to lock into one another. This makes sliding friction smaller than static friction.

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

Answer: Friction is a friend because it allows us to hold a pen in our hands. This force also helps us to warm our hands during winters when we rub our hands together.

Friction is a foe because friction between leaves of trees can start a fire in the forest. It can also cause damage to parts of a machine.

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

Answer: Objects moving through fluids have streamlined shapes to reduce the friction due to fluid.

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