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A pulley is a mechanical device that can be used to lift heavy objects more easily. Pulleys consist of a wheel that rotates on an axle, which is a rod through the center of the wheel, and a rope, cable, or chain. There are three main types of pulleys: fixed, movable, and compound.
The key scientific concept for pulleys is that they redirect force. For example, instead of pushing a load up, you can attach it to a rope and pulley above you and pull down to move it up. All pulley systems re-direct force.
Pulleys are often used to lift heavy objects, allowing a worker to use less force to move the object. Looping the rope over more wheels increase the upward force. Using two wheels means you can lift something twice as heavy using the same force.
Double Pulley System
Triple Pulley System