Contact between bodies such that the relative velocity of the two contacting surfaces at the point of contact is zero. Common applications of rolling contact are the friction gearing of phonograph turntables, speed changers, and wheels on roadways. Rolling contact mechanisms are, generally speaking, a special variety of cam mechanisms. An understanding of rolling contact is essential in the study of antifriction bearings. The concepts are also useful in the study of the behavior of toothed gearing.