CBSE Class 8 Answered
When a body slides ( or rolls ) over a surface, a force starts acting on the body, in a direction opposite to the motion of the body, along the surface in contact. This is called the frictional force or the force of friction.
There are three types of friction :
1) Static friction- The friction that exists between the two surfaces in contact when there is relative motion between them is about to start is called static friction.
2) Kinetic friction-The friction that exists between a surface sliding on another surface is called kinetic friction.
3) Rolling friction-When a body rolls on the the surface of another, the friction that exists between the surfaces is called static friction.