motion and friction

 

It is to be noted that action and reaction do not act on the same body.If they acted on the same body, resultant force would be zero.Thus forces appear in pairs.Infact, the action and reaction are different aspects of the same force and hence co-exist.

When a person walks, he presses the ground in the backward direction ( action) and the ground exerts an equal and opposite force on the person in the forward sdirection ( reaction) . This force R can be resolved into two components - a horizontal component and a vertical component . The vertical componentbalances the weight, while the horizontal component pushes him forward.