Pulley

Pulley, grooved wheel mounted on a block with a cord or belt passing over it. A pulley is a simple machine applying the equilibrium of torque to obtain a mechanical advantage. Thus the block and tackle is a combination of ropes and pulleys used for hoisting heavy weights. A belt and pulley combination can transmit motion from one part of a machine to another. Variable speed can be obtained from a single-speed driving shaft by the use of stepped or cone-shaped pulleys with diameters that give the correct speed ratios and belt tensions. To help prevent excessive belt wear and slipping, the rim surface of a pulley is adapted to the material of the belt used.