Types of pulleys include fixed, movable, compound and block and tackle. Fixed pulleys have immobile axels, which prevents rotation. Axels of movable pulleys, in contrast, feature bases with free axels, which allows for greater rotation and the transfer of forces.
Fixed and movable pulleys demonstrate the two primary mechanical compositions of pulley systems. Compound pulleys merge elements of stationary and mobile pulleys, as do block and tackle pulleys. Block and tackle pulleys contain multiple compound pulleys to form a complex system. Regardless of type, pulley systems share similar designs.
Pulley units consist of round discs attached to thick, durable ropes. Simple pulleys have two discs, while complex systems contain many more. Pulleys contain two loops running through their axels, which allows for the equal distribution of weight. That, in turn, prevents pulleys from breaking under excessive forces. Historians remain unclear as to when pulleys arrived. However, evidence suggests that people in Mesopotamia employed pulleys for transporting water; Archimedes first produced written evidence of using pulleys to move his warships. Pulleys still see use on ships and water vessels. Other industries, such as construction, also use pulleys. Pulleys come in a variety of sizes, and adhere to cranes, trucks and other types of industrial equipment.