Pulleys are used in a variety of ways to afford mechanical advantages in lifting heavy loads, applying forces, and to transmit power. In the real world, the usages of pulleys are seen in different load carrying activities. Simple pulleys are used in lifting building materials at construction sites, hoisting a flag, elevators and other simple load-carrying tasks. Compound pulleys are used in cranes, industrial material handling systems and lawn mowers.
Pulleys have been used by human beings for thousands of years. Ancient people used pulleys in their work, and the Greek mathematician Archimedes was one of the first to describe its mechanism mathematically.
Now, pulleys have been modified from simple systems to compound systems, to help people lift heavier loads more easily. Pulleys are assembled to form a block and tackle to help raise heavy weights. This system can be defined as a set of pulleys assembled so that they rotate independently on the same axle to form a block. The mechanical advantage of the block and tackle is the same to the number of rope parts that support the moving block. Block and tackle systems are often attached to powerful motors in cranes at construction sites and shipyards to lift heavy loads.