Simple machines (levers, pulleys, inclined planes, and wedges) are used to reduce the effort needed to perform certain tasks, making them more convenient. Although pulleys operate on the same principle as levers, there is a significant difference between them. While levers produce only limited displacement, the use of ropes, cables, or chains allows pulleys to enable continuous lifting.

A pulley is a disc with a groove around its circumference used to lift a load by using ropes. The fixed pulley has a fixed axis. The load is lifted by means of a rope slung around the pulley. On construction sites, for example, the mortar bucket is lifted to the upper floor with the help of a fixed pulley.

• In a  fixed pulley , both the effort arm and the load arm are the radius of the pulley, so the force required to lift the load is equal to the weight of the load, but the direction of the force can be varied at will. Both the lifting force and the load pull the pulley in the same direction, so it is subjected to twice the load force.
• In the case of a  movable pulley , the load is suspended on its axis of rotation. One end of the rope is fixed high and the other end is raised. One half of the load pulls on one end of the rope, the other half pulls on the other end. To lift the load, it is sufficient to exert half its weight, but twice the displacement is required.

In practice, usually several stationary and movable pulleys are connected. The resulting system is called a compound pulley system. One type of this is the block and tackle, which consists of the same number of stationary and movable pulleys around which a single rope is slung. When used, the force required to lift the load uniformly is the 1/(2n) part of the gravitational force acting on the load, where n is the number of movable pulleys in the pulley system: F=G/2n.