Friction

What is friction

It is a force which opposes motion of one object over another object in contact with it

In easy language,it is a force which makes moving object stop

Example 1

A ball which is moving comes to rest after some time

This is due to force of friction between ball and ground

Example 2

Boat comes to rest if we stop rowing

This is because of the force of friction between water and the boat

What is direction of force of friction?

Friction always acts in the opposite direction of motion

If we push a book on table from left to right 

Force of friction moves in opposite direction from right to left

Similarly, if we push a book on table from right to left

Force of friction moves in opposite direction from left to right

What causes friction?

If we take a microscope and zoom in the surface of two objects,

we see that both the surface have some irregularities

When we try to move the object, the irregularities gets interlocked. This causes friction

So,

rougher the surface, more the irregularities. Hence, more friction

smoother the surface, less the irregularities. Hence, less friction