Friction and its types.

FRICTION :

The opposing force which comes into play in between the surfaces of two bodies when one body is moved over the surface of another body is called force of friction or friction.
Whenever there is a relative motion between the two surfaces in contact, an opposing force comes into play to prevent the relative motion. This opposing force is called force of friction.

Cause of Friction: The surfaces of solid bodies are not perfectly smooth. Friction is produced by the interlocking of irregularities of one surface with that of the other surface in contact.

Types of Friction :

1. Static Friction : The friction offered by the surfaces in contact subjected to external forces until there is no motion between them is called static friction.

2. Limiting Friction : The maximum value of friction which comes into play when a body just starts moving over the surface of another body is called limiting friction.

3. Dynamic Friction : The force acting between the surfaces when there is a relative motion between the two surfaces in contact is called the force of dynamic or kinetic friction.
Note : Dynamic friction less than the static friction and limiting friction.

4. Rolling Friction : When a circular body (wheel, ring, sphere) rolls over the surface of another body, the force of friction that comes into play between the two surfaces is called rolling friction.