28/1/21                                          Friction a s a Force- 12

Answer the following:

1. What is meant by the force of friction?

A. The force that comes into action when two objects or surfaces are in contact is called as force of friction.

2. How does friction help us while walking?

A. The force of friction between our leg and floor (ground) helps us in walking.

3. Why do tyres of vehicles have to be replaced regularly?

A.  Due to continuous use of tyres of vehicles the grooves will get worn out which is an effect of friction, so it has to be replaced to get good grip on road.

4. Explain the effects of friction.

A. 1. Slows down a moving object.

     2. Produces heat

     3. Causes wear and tear.   

5. What is a lubricant and why is it used? Give examples.

A. The substance used to reduce friction are called as lubricants. eg: Oil, grease, powder etc.

Textbook:

A. 1. smooth        2. greater       3. friction     4. Spikes       5. Anti-skid

B. 1. True      2. True     3. True      4. False        5. False.

4. Weightlifters rub their hands with sawdust or rough powder before lifting weights.

5. Rollers decrease friction by reducing the contact area of the surfce.

HW.   :   Text book: Page 119 C

                  Worksheet 11