Explore the clever mechanics behind pulleys in Jiwi's Machines Episode 2. Discover how simple systems create powerful movements in this exciting Science Extra feature.

EXPLANATION: A pulley is one of the six simple machines. Single pulleys were part of simple cranes invented more than 3,000 years ago. A pulley consists of a wheel that is free to turn its center.

With a simple pulley the force you must exert is equal to the weight of the load. With a compound pulley—two or more pulleys combined together—you can reduce the force required to lift the load.