Frictional force is something that tries to stop the movements of an object already resting in one condition. This is best understood with one example:
Suppose one solid block of mass or ‘m’ is resting on the rough surface, consider this picture:
- The force used to pull that mass is P and in its initial moment that m is unable to move.
- The reason behind this is F which is delivering a counter force to stop m from going into the direction P is pulling.
- The more P tries to pull F increases with each moment.
- You will find this m starts to move or slide on that rough surface only when P pulls with highest force.
Consider this figure:
That block of mass will reach equilibrium in this condition.
Let us find the equations to solve this:
First, ∑Fx= 0
P – F =0
F = p
Then, ∑fy= 0
N – mg = 0
N = mg