Kinetic Friction | Dynamic Friction | Sliding Friction
  
 
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.
Without     confusing the two, the difference between static     friction and kinetic friction is that static friction occurs when the object     is stationary, that is, not moving, while kinetic friction takes place when the     object has started moving. It is kinetic friction that makes sure an object does     not continue to move forever when a force has acted on it as stated in Newton’s     first law of motion .       
As     is the case with static friction, kinetic friction depends on the nature of the     materials or surfaces in contact, and the magnitude of the force that set the     body in motion. However, kinetic friction is less than static friction for the     same material surfaces in contact.
Kinetic  friction can be demonstrated in the laboratory by the following experiment:
A  wooden block placed on a wooden table is given a push to move it. It moves  forward for a while, slows down and come to a halt. It slows down because of the  kinetic friction that acted on its velocity, in the opposite direction to its  motion, which eventually brings it to a stop.
To  offset the existing kinetic friction between the wooden surfaces of both the  block and the table, additional forward force is required. This is made possible  by attaching a string to the block, and weights attached to the other end of the  string. With the aid of a pulley system as shown below, the attached weights  generate a forward force on the block making it to continue moving.
 
 
By    attaching the right weights on the string, the block will continue moving at    constant velocity. At this point the net force acting on the block is zero.
The  kinetic friction acting between the surfaces of two bodies in relative motion to  each other is represented by the formula: