ABSTRACT
Friction is defined as the force resisting motion when two contacting surfaces are moved relative to each other. In a dry system, this force is a result of interaction between the surfaces involved; a fundamental difference exists in the nature of this interaction depending on whether the motion is of a sliding or a rolling character. An understanding of the fundamental mechanism of friction presumes an appreciation of the nature of nominally flat surfaces on a microscopic scale. This shows a finely polished finish as a series of hills (asperities) and valleys (troughs) of finite dimensions, while normal engineering finishes are viciously contoured. Hydrodynamic lubrication is the term used to cover the regime where complete separation of the moving surfaces has been attained throughout the majority of service. Its achievement depends on geometrical design and maintenance of adequate speed of movement.
