A pulley is a simple machine that consists of a wheel with a groove in which a rope or cable can run. It changes the direction of force applied to it and can be used to lift or move objects.
Related terms
Tension: The force transmitted through a string, rope, cable, etc., when it is pulled tight by forces acting from opposite ends.
Mechanical Advantage: The ratio of output force exerted by a machine to the input force applied to it.
Friction: The resistance encountered when two surfaces slide past each other. In the case of pulleys, friction can affect their efficiency and cause loss of energy.