Pulley

A pulley, also called a sheave or a drum, is a mechanism composed of a wheel on an axle or shaft that may have a groove between two flanges around its circumference.[1] A rope, cable, belt, or chain usually runs over the wheel and inside the groove, if present. Pulleys are used to change the direction of an applied force, transmit rotational motion, or realize a mechanical advantage in either a linear or rotational system of motion. It is one of the six simple machines. Two or more pulleys together are called a block and tackle

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.

Overall, no matter how easy it is to use the pulley system, the system itself is not very efficient due to the force of friction. For example, one has to pull two meters of rope of cable through the pulleys in order to lift an object one meter.