Define angle of friction

Define angle of friction. The inclination \teta of a rough plane is increased gradually. The ply on the plane just comes into motion when inclination 6 becomes 30°. Find coefficient of friction if the inclination is further increased to 45°. Find acceleration.

Angle of Friction : The angle which the resultant of force of limiting friction F and normal reaction R makes with direction of normal reaction R is called angle of friction.