# Friction

It is an opposing force which comes into play when one body actually moves (sides or rolls) or even tries to move over the surface of another body. Frictional force arises due to interlocking of irregular present on the two surfaces in contact. According to modern view, the frictional force arises due to strong atomic or molecular forces of attraction between two surfaces at the point of actual contact.

### Static friction

It is an opposing force which comes into play when one body tends to move over the surface of another body, but the actual motion has yet not started. It is a self adjusting force.

### Limiting Friction

It is the maximum value of static friction. Limiting friction is maximum opposing force that comes into play when one body is just at the averge of moving other the surface of another body.

### Rolling friction

It is an opposing force which comes into play when one body is actually rolling over the surface of another body. The value of rolling friction is much smaller than the sliding friction.

### Rigid body

A rigid body is a system of particles, in which distance between any two particles does not change under the influence of external forces.