The pulley is a circle around the central axis of the wheel. The circumferential surface of the circular wheel having a groove, the rope wound on the grooves, the force La Shengsuo Either end of pull, and the circle round the rope will lead to friction between the circle around the central axis of the wheel. Press the central axis of the pulley is moving, the pulley can be divided into"fixed pulley ","pulley "; fixed pulley center axis is fixed, the central axis of the
movable pulley can be moved. The main function is to pull the pulley load force changes direction, the transmission power and so forth. Composed of a plurality of pulleys machine called a"pulley ", or "double pulley." The mechanical advantage of the pulley is large, can pull heavier loads. Can also be a chain wheel or belt drive assembly, the power transmitted from a rotating shaft to the other rotating shaft.
Pulley is
deformed lever, simple machine belong leveraged, very versatile. Only effort but also can change the direction of the force. Move together with the central axis of the pulley weights called movable pulley, the lever arm is deformed unequal ( effort lever ), you could save half the power, but fees doubled the distance ( movable pulley rise n m, string up the free end 2n m, n ≥ 0), and can not change the direction of the force. The fixed pulley cord matter where to force direction, the force used to lift weights are equal (rope weight and friction between the rope and the wheel does not count ) ( power arm and the resistance arms are equal and equal to the radius of the pulley ); movable pulley cord vertically upward direction of the force with minimal effort.
About pulley painted products first appeared in an eighth century BC Assyrian reliefs. This relief show is a very simple pulley, can only change the direction of force, the main purpose is to facilitate the force, and does not give any mechanical advantage. In China, the drawing of the pulley device first appeared in the Han Dynasty brick, ceramic mold wells. In "Ink Sutra" is also recorded on the pulley exposition.
The ancient Greeks would be classified as a simple machine pulley. As early as 400 BC, the ancient Greeks already know how to use a double pulley. Around 330 BC, Aristotle wrote in his book"mechanical problems"in the eighteenth question, specifically discuss "double pulley"System Archimedes contribute a lot about simple machines knowledge of the pulleys is explained in detail kinematics theory. Archimedes is said to have sole use of double pulley pulling a cargo and passengers filled the big ship, the first century AD, Hero of Alexandria wrote about the analysis and the theory of double pulley proved load and force bear the load is equal to the ratio of the number of segments of the rope, the"pulley principles."
Pulley block is determined by a number of pulleys and pulley match is made, you can reach both the effort and the purpose of changing the direction of force. Use, and how much effort the rope around the law, depending on the use of pulley effect. Assumed to be two rope pulleys that every object and the movable pulley rope assume power is the object and the movable pulley fraction of the total weight.
