Friction that opposes the motion of a ball (or other object) when it rolls across a surface. Rolling friction occurs because the ball and the surface upon which it rolls are deformed slightly during contact. The magnitude of the rolling friction between dry surfaces is influenced by the coefficient of friction between the surfaces in contact, the normal reaction force, the radius of curvature of the ball, and the deformability of the rolling object. The amount of rolling friction is changed dramatically if a liquid occurs between the surfaces. Synovial fluid decreases the rolling friction in a ball-and-socket joint. Presence of a liquid can change the nature of a surface on which a ball rolls. For example, rain makes grass both wet and soft, increasing rolling friction and slowing down a ball.
Subjects: Sports and Exercise Medicine.