# Friction Extra questions

In this page we have Friction Extra Questions for Class 8 . Hope you like them and do not forget to like , social share and comment at the end of the page.

Question 1.
(i)What is limiting friction?
(ii)What is dynamic friction?
(iii)What is sliding friction?
(iv)What is rolling friction?
(v)What is fluid friction?

(i)The maximum force that is required to move an object from other object’s surface is called limiting friction.
(ii)Friction between two bodies when one body is moving with a uniform velocity upon the other body is called dynamic friction. It includes sliding friction and rolling friction both.
(iii)A force of friction that is produced when an object slides upon the surface. So, the area of contact between the object and other surface produces friction, called sliding friction.
(iv)A force of friction produces when an object rolls over the surface of other is called rolling friction.
(v)A force of friction produces when the body moves through the fluid. The area of contact between the body and fluid produces friction, called fluid friction or drag.

Question 2.
Raman performs an experiment in which he first slides a wooden log (100 kg) and then slides a wooden box (100 kg). He observed that he needs to put some extra energy while pushing the wooden box. Why?

According his experiment, he noticed that the wooden log is cylindrical in shape while the wooden box is a cube-shaped therefore, while rolling the wooden log, rolling friction applied and sliding the wooden box applied the static friction. As we know, friction decreases in the case rolling friction. Moreover, rolling friction is less than static friction. Thus, Raman rolls the wooden log easily whereas he applies a great amount of energy for pushing the wooden box.

Question 3.
What factors effects the fluid friction?

The factors that effects the fluid friction are shape of the object, speed of the object and nature of the fluid.

Question 4.
Why submarines have streamlined body?

Submarines have streamlined body to experience less amount of friction while moving through water.

Question 5.
Why do we use ball bearings in the tyres?

We use ball bearings in the tyres because these ball bearings convert sliding friction into rolling friction which makes the movement easier.

Question 6.
How do we change rough surfaces into smooth surfaces?

We change rough surfaces into smooth surfaces by polishing them.

Question 7.
Why do weightlifters use powder before lifting the weight?

Weightlifters use powder before lifting the weight because it increases the friction and provides a firm grip while lifting the weight.

Question 8.
How does matchstick lights up?

By rubbing the matchstick on its cover, friction produces the heat that lights up the head of the matchstick.

Question 9.
How do we walk on the road while walking on the grass less soil makes us fall?

We walk on the road because friction helps us to provide a grip while walking on the grass less soil is difficult because there is no friction.

Question 10.
With the help of an experiment, explain the effect of rolling friction is less than sliding friction.

1. Take two 50 kg blocks of cylindrical and cube shapes. Mark two points in your courtyard A and B at distance of 100 m. Take a stopwatch and observe the time in both the cases.
2. First, try to slide the cube block from point A to point B.
3. Second, try to slide the cylindrical block from point A and point B.
4. You noticed that cube block took 10 minutes and required a great amount of energy to push it from point A and point B whereas, cylindrical block took only 2 minutes and less energy.
5. Thus, this experiment shows that rolling friction is less than sliding friction.

Question 11.

## Summary

This Friction Extra Questions for Class 8 is prepared keeping in mind the latest syllabus of CBSE . This has been designed in a way to improve the academic performance of the students. If you find mistakes , please do provide the feedback on the mail.