Pulley

详情

A pulley is made from a wheel and a rope. It is used to make lifting easier. A single pulley changes the direction of the lifting force. For example, if you are lifting a heavy object with a single pulley anchored to the ceiling, you can pull down on the rope to lift the object instead of pushing up. The same amount of effort is needed as without a pulley, but it feels easier because you are pulling down. If you add a second pulley, the amount of effort to lift the heavy object is much less *- half as much. However, you will have to pull the rope further. A double pulley can help you to lift objects you could never lift without it. Pulleys are also used on elevators. Pulleys are also used on cranes to hoist things up.