A pulley is a simple machine made of a wheel with a grooved rim that a rope or cable runs through. When you pull down on one end of the rope, the pulley helps you lift something heavy on the other end.

Pulleys make lifting easier by changing the direction of your force. Instead of trying to hoist something straight up, which is awkward and exhausting, you can pull down using your body weight. Even better, when you combine multiple pulleys together (called a pulley system), you can multiply your strength. With the right setup, you could lift a piano that would be impossible to budge otherwise.

You see pulleys everywhere once you start looking: flagpoles use them to raise flags, theaters use them to lift stage curtains and scenery, construction cranes use them to hoist steel beams, and even old-fashioned wells used pulleys to bring up buckets of water. Window blinds often use tiny pulleys, too.

The pulley is one of the six classical simple machines that form the foundation of how we move and lift things. Engineers have relied on pulleys for thousands of years because they work beautifully and don't need batteries or fuel.