Weights are used as a source of energy when uniform pressure or action is desired. The proper tension is maintained on a rope by means of a weight suspended on a movable pulley. There are many applications of weights as a motive force, but when they are used, the action is comparatively slow.

They are sometimes employed as the motive force for large clocks, such as those installed in towers.

A clock or watch contains three important pieces of mechanism or elements: (1) the source of energy to move the parts, which is a suspended weight in large clocks or a spring in small clocks and in watches; (2) the series of wheels, called a train of wheels, or gears, operated by the driving force; and (3) a device for controlling the movement of the train of gears.