pulley · groove · crane · elevator · strength
The pulley is the sixth simple machine. It works like a wheel but has a groove around its edge. A rope sits inside the groove, and when you pull one end of the rope, the pulley lifts a load on the other end. Using several pulleys together multiplies your strength, allowing you to lift extremely heavy objects. Cranes use large pulleys to lift heavy steel and concrete to build skyscrapers all around the world. Elevators also use pulley technology to carry people safely and smoothly between different floors of a building. The pulley is one of the most useful machines ever invented.