The term pulley or pulley system is used for any of a number of related simple machines, having the following features:
- A rotatable wheel.
- A rope or belt or string passing over and around the wheel, and curving over it, so that linear motion of the rope corresponds to rotation of the wheel.
A pulley is a simple machine that works by changing the direction -- the direction in which the rope hangs at one end can differ from the direction in which the rope hangs at the other end, allowing the application of a force in one direction to move a load in another direction.
Here are some examples of pulley systems in action:
|fixed pulley with vertical loads||300px|
|pulley system on a double inclined plane|
|pulley system for block piled on block||300px|