A pulley is a simple machine consisting of a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and the cable or belt. Pulleys are used to transmit energy and motion, and they can be used singly or in combination to gain mechanical advantage, especially for lifting weights. The main parts of a pulley are the wheel, axle, and rope. There are two main types of pulleys:
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Fixed pulley: A fixed pulley has an axle mounted in bearings attached to a supporting structure. It changes the direction of the force on a rope or belt that moves along its circumference. Mechanical advantage is gained by combining a fixed pulley with a movable pulley or another fixed pulley of a different diameter.
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Movable pulley: A movable pulley has an axle in a movable block. A single movable pulley is supported by two parts of the same rope and has a mechanical advantage of two. Combining two or more pulleys increases the number of loops and reduces the effort required to lift the object.
Pulleys can be used in sets designed to reduce the amount of force needed to lift a load. However, the same amount of work is necessary for the load to reach the same height as it would without the pulleys. The magnitude of the force is reduced, but it must act through a longer distance.
