Pulley History Notes

The earliest depiction of a pulley appears in an Assyrian relief from the eighth century BC. This relief shows a very simple pulley that can only change the direction of force application. Its main purpose is to facilitate the application of force and does not provide any mechanical benefit. In China, the drawing of pulley devices first appeared on portrait bricks and pottery well molds in the Han Dynasty.
The ancient Greeks classified pulleys as simple machines. As early as 400 BC, the ancient Greeks already knew how to use compound pulleys. Around 330 BC, Aristotle devoted the eighteenth question in his book "Mechanical Problems" to studying the "complex pulley" system. Archimedes contributed a lot of knowledge about simple machines. , explain the kinematic theory of pulleys in detail. It is said that Archimedes once used a compound pulley alone to pull a large sea ship filled with cargo and passengers. In the first century AD, Hero of Alexandria analyzed and wrote the theory about compound pulleys, proving the load and force application. The ratio of is equal to the number of rope segments carrying the load, that is, the "pulley principle".
In 1608, in his book "Mathematical Collection" (Mathematical Collection), the Dutch physicist Simon Steffen showed that the ratio of the length of the moving path between the force exerted by the pulley system and the load is equal to the ratio between the applied force and the load. Inverse ratio. This is the rudimentary principle of virtual work.
In 1788, French physicist Joseph Lagrange used the pulley principle to derive the principle of virtual work in his masterpiece "Mécanique analytique", thus kicking off Lagrangian mechanics.
In our country, there are records about pulleys in the book "Mo Jing" written by Mo Zhai (known as Mozi) and his disciples in Guisi (388 BC), the 14th year of King Zhou An. The pulley with a fixed central axis is called a fixed pulley, which is a deformed equal-arm lever that does not save effort but can change the direction of the force. The pulley whose central axis moves together with the weight is called a movable pulley. It is a deformed unequal arm lever that can save half the force but does not change the direction of the force. In practice, a certain number of movable pulleys and fixed pulleys are often combined into various forms of pulley blocks. The pulley block saves effort and can change the direction of force.
The differential pulley (commonly known as a hand chain hoist) commonly used in factories is also a pulley block. Pulley blocks are widely used in cranes, hoists, lifts and other machinery.