Pulley

A pulley is a simple machine made of a wheel with a groove and a rope that fits into the groove. You pull on one end of the rope, and the other end lifts a load. Pulleys make it easier to lift heavy things.

The simplest kind is a single fixed pulley. The wheel is attached to something above, like a beam or a ceiling. A rope runs over it. When you pull the rope down, the load goes up. You still have to pull with the same force as the load weighs. But pulling down is easier than lifting up, because you can use your body weight to help.

A movable pulley is different. The wheel hangs on the rope along with the load. With a movable pulley, you only need half as much force to lift the weight. The trade-off is that you have to pull the rope twice as far.

When you combine fixed and movable pulleys, you make a block and tackle. These systems can lift very heavy loads with a small pull. Sailors used them to raise huge sails on old ships. Construction workers still use them today to lift beams and engines.

You can find pulleys at the top of flagpoles, inside elevators, and on window blinds.