^Motion of a body on a fixed rough horizontal surface 

^Motion of a body on a fixed rough horizontal surface 

Suppose a block of mass ‘m’ placed on a rough horizontal plane is pulled by a horizontal force F.

Following are the various possibilities:

1. If F = 0, then the frictional force acting on the block will be zero & the block will remain stationary.
2. If F < f_L, then the frictional force acting on the block will be equal to F & the block again will remain stationary.
3. If F = f_L, then the frictional force acting on the block will be equal to f_L & the block will be at the verge of motion i.e. about to move.
4. If F > f_L, then the frictional force acting on the block will be equal to f_K & the block will move with acceleration   a= f- f_k /m   in the direction of force applied F.