Use of Pulleys (Antiquity)
Introduction
A pulley is a simple machine, a mechanical traction device, that serves to transmit a force. It consists of a wheel with a channel on its periphery, through which a rope passes that rotates about a central axis. Furthermore, forming assemblies—rigs or hoists—serves to reduce the magnitude of the force necessary to move a weight.
According to Goupillière's definition, "the pulley is the support point of a rope that, moving, wraps itself around it without making a complete turn"[1] acting at one end as resistance and at the other as power.
The first evidence of pulleys dates back to Ancient Egypt in the Twelfth Dynasty (1991-1802 BC)[2] and Mesopotamia at the beginning of the second millennium BC. C.[3] In Roman Egypt, Heron of Alexandria (c. 10-70 CE) identified the pulley as one of six simple machines used to lift weights.[4] Pulleys are assembled to form a block and tackle in order to provide mechanical advantage for applying large forces. Pulleys are also assembled as part of a belt and chain drive to transmit power from one rotating shaft to another. Plutarch's work Parallel Lives recounts a scene in which Archimedes demonstrated the effectiveness of compound pulleys and the locking and hitching system by using one of them to pull a fully loaded ship toward him as if it were sliding through the water.[7]
History
The only historical note on its use is due to Plutarch, who in his work Parallel Lives (c. 100 BC) relates that Archimedes, in a letter to King Hiero of Syracuse, with whom he was a great friend, stated that with a given force he could move any weight and even boasted that if another Earth existed, by going to it he could move this one. Hiero, astonished, asked Archimedes to give a demonstration.
They agreed that the object to be moved would be a ship from the king's navy, since Hiero believed that it could not be removed from the dock and taken to dry dock without the use of great effort and numerous men. According to Plutarch, after loading the ship with many passengers and with the holds full, Archimedes sat at a distance and, pulling the rope, lifted the ship without great effort, taking it out of the water as upright and stable as if it were still in the sea.[8].