rolling friction

rolling friction, type of friction that occurs when a wheel, ball, or cylinder rolls freely over a surface, as in ball and roller bearings. In general, friction is the force that resists the sliding or rolling of one solid object over another. The main source of friction in rolling appears to be dissipation of energy involved in deformation of the objects. If a hard ball is rolling on a level surface, the ball is somewhat flattened and the level surface somewhat indented in the regions in contact. The elastic deformation or compression produced at the leading section of the area in contact is a hindrance to motion that is not fully compensated as the substances spring back to normal shape at the trailing section. The internal losses in the two substances are similar to those that keep a ball from bouncing back to the level from which it is dropped.

Coefficients of rolling friction are generally 100 to 1,000 times less than coefficients of sliding friction for corresponding materials. This advantage was realized historically with the transition from sledge to wheel. (See mechanics.)

Other types of friction include static friction and metal adhesion.