define angle of friction with diagram

Suppose a body is resting on a horizontal rough surface. A force F is applied to it such that a frictional force f nullifies the applied force and the body is in the verge of movement.

The angle made by the resultant of the normal force and the frictional force with the normal is called the angle of friction.

We have,

N = W

f = µW = F (since the body is on the verge of movement)

Therefore,

tanθ = f/N = µW/W = µ

= > θ = tan^-1µ

θ is the angle of friction.