pulleys

A pulley is a wheel with a grooved rim that guides a rope, belt, or cable. Pulleys are used to transmit force, change direction, or provide mechanical advantage when lifting or moving loads.

A fixed pulley is attached to a support; it merely changes the direction of the input force. A movable pulley attaches to the load, and the rope supports the load on multiple segments, reducing the required input force. A compound pulley, or block and tackle, combines fixed and movable pulleys to increase mechanical advantage, at the cost of more rope length and complexity.

In an ideal system, the mechanical advantage equals the number of rope segments supporting the load, and the velocity ratio matches that number. Real systems include friction, rope bending losses, and elasticity, which reduce efficiency.

Typical components include the sheave (the wheel), the groove, and the axle. In block-and-tackle arrangements, multiple pulleys are housed in two or more blocks connected by a rope.

Applications span construction cranes, elevators, theater rigging, sailing, mining equipment, and gym machines that use pulley-based resistance.

Pulley devices have ancient origins; evidence from ancient Egypt and Greece shows early use, with later formalizations in studies of simple machines and lifting systems.