CBSE Class 11-science Answered

When two bodies that are not moving relative to each other are in contact, the friction force acting between their surfaces is known as static friction or limiting friction. This friction force will prevent one of the bodies from moving over the other, or sliding down a slopped surface, except an applied force is greater than it.

Static friction F_s, also known as limiting friction, is the maximum friction force that is produced and which must be overcome for a body to move over, or slide down the surface of another body.

Kinetic friction, also known as dynamic or sliding friction occurs when a body is in relative motion with another, with their surfaces in contact. It is the frictional force that slows down, and eventually stops a moving object.

For example, a soccer ball given a slight kick will begin to roll on the pitch, then slows down, and then come to a stop. The ball is slowed down, and then stopped after it has started moving with a velocity, as a result of the kinetic friction between its surface and the pitch.