# Force of friction and their types

Friction is the property of two surfaces is contact by virtue of which each surface resists the relative motion of the other surface. Thus when a body moves or tends to move tangentially with respect to the surface, on which it rests, the interlocking property of the projecting particles opposes the motion.

Friction force diagram

This opposing force which acts in the opposite direction of movement of the body is called force of friction or simply friction.
There are two types of friction –

1. Static friction
2. Dynamic friction or kinetic friction

## Static friction

When body is at rest or tends to move, the friction between the contact surfaces is called static friction.

## Dynamic friction

When a body is in motion over a surface the friction between the contacts surface is called dynamic friction or kinetic friction.

This is two types depend on types of motion as –
Sliding friction: When one body slides over other e.g. skiing over ice.
Rolling friction: When one body rolls over the other e.g. a bicycle running over the road.
Related topic –
Law of friction