Pulleys are one, or several wheels, on an axle or shaft that support the movement and a change of direction of a cable or belt (that is usually taut). They transfer power between the shaft and cable and provide an immense mechanical advantage for providing large forces ideal for lifting heavy objects.
Pulleys come in various types:-
- A fixed pulley has an axle mounted in bearings attached to a supporting structure
- Movable pulleys have axles mounted on movable blocks.
- Compound pulleys are a mixture of the above two. The perfect example is the block and tackle pulley system.
The pulley was identified by the great Heron of Alexandria as one of the six simple machines. Today pulleys are an integral part of many mechanical systems including fan belts, flag poles, and water wells.