What is friction, limiting equilibrium and the coefficient of friction µ?

In this tutorial I show you and introduce the equation F = µR.

Example 1 – Horizontal Plane

A block of mass 20 kg rests on a rough horizontal plane. The coefficient of friction between the block and the plane is 0.25. Calculate the frictional force acting on the block when a horizontal force of i) 40 N ii) 53 N acts on the block. In each case state whether the block will move and if so find its acceleration.

Example 2

A particle of mass 10 kg lies on a rough horizontal plane. A force P of 25N acts on the particle at 30° above the horizontal. If the coefficient of friction is 0.2. Will the particle move and if so with what acceleration?