A wheel guiding a rope or cable so that it can redirect a tension force. An ideal fixed pulley changes the force direction without multiplying its magnitude. A freely rotating pulley with negligible moment of inertia and friction has equal rope tensions on its two sides; a finite moment of inertia instead relates their difference to its angular acceleration through the net torque.
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A pulley is a simple machine that consists of a grooved wheel and a rope, cable, or belt that runs along the groove. It is used to change the direction of a force applied to an object and can also create a mechanical advantage, making it easier to lift heavy loads. Pulleys can be used alone or in combinations, known as pulley systems, to lift or move objects vertically or horizontally.