Notice that both of these friction formulas ONLY depend on the coefficient of friction and the normal force. It does not depend the area of contact, it doesn't depend on the sliding speed.

Note that the normal force acting on P switches from contact on the outer surface (normal force pointing inward) to contact on the inner surface (normal force pointing outward) and back to contact on ...

The type of force involved may also be shown. Weight, normal contact force and friction for an object moving at constant speed down a hill. The effect of the horizontal force to the left is equal ...