Pulley

1º.- A pulley is a wheel with a groove along its edge, for holding a rope or cable. Pulleys are usually used in sets designed to reduce the amount of force needed to lift a load. However, the same amount of work is necessary for the load to reach the same height as it would without the pulleys. The magnitude of the force is reduced, but it must act through a longer distance.

Types of pulleys

1º Fixed:

A fixed pulley has a fixed axle. That is, the axle is ""fixed"" or anchored in a place ( maybe the roof, ..). A fixed pulley is used to redirect the force in a rope ( when it goes in a full circle, it is called a belt). A fixed pulley has a mechanical advantage of 1.

2º Movable:

 A movable has a free axle. That is, the axle is "free" to move in space. A movable pulley is used to transform forces. A movable pulley has a mechanical advantage of 2. That is, if one end of the rope is anchored, pulling on the other end of the rope will apply a doubled force to the object attached to the pulley.