Back Katrol AF በከራ AM Carrucha AN घिरनी ANP بكرة Arabic Polea AST Blok (mexanika) AZ Moton BCL Блок (механіка) BE Блёк BE-X-OLD
| Pulley | |
|---|---|
 Pulleys on a ship. In this context, pulleys are normally known as blocks. | |
| Classification | Simple machine |
| Industry | Construction, transportation |
| Wheels | 1 |
| Axles | 1 |
A pulley is a wheel on an axle or shaft enabling a taut cable or belt passing over the wheel to move and change direction, or transfer power between itself and a shaft. A sheave or pulley wheel is a pulley using an axle supported by a frame or shell (block) to guide a cable or exert force.
A pulley may have a groove or grooves between flanges around its circumference to locate the cable or belt. The drive element of a pulley system can be a rope, cable, belt, or chain.
The earliest evidence of pulleys dates back to Ancient Egypt in the Twelfth Dynasty (1991–1802 BC)[1] and Mesopotamia in the early 2nd millennium BC.[2] In Roman Egypt, Hero of Alexandria (c. 10–70 AD) identified the pulley as one of six simple machines used to lift weights.[3] Pulleys are assembled to form a block and tackle in order to provide mechanical advantage to apply large forces. Pulleys are also assembled as part of belt and chain drives in order to transmit power from one rotating shaft to another.[4][5] Plutarch's Parallel Lives recounts a scene where Archimedes proved the effectiveness of compound pulleys and the block-and-tackle system by using one to pull a fully laden ship towards him as if it was gliding through water.[6]
- ^ Arnold, Dieter (1991). Building in Egypt: Pharaonic Stone Masonry. Oxford University Press. p. 71. ISBN 9780195113747.
- ^ Moorey, Peter Roger Stuart (1999). Ancient Mesopotamian Materials and Industries: The Archaeological Evidence. Eisenbrauns. p. 4. ISBN 9781575060422.
- ^ Usher, Abbott Payson (1988). A History of Mechanical Inventions. USA: Courier Dover Publications. p. 98. ISBN 0-486-25593-X.
- ^ Uicker, John; Pennock, Gordon; Shigley, Joseph (2010). Theory of Machines and Mechanisms (4th ed.). Oxford University Press, USA. ISBN 978-0-19-537123-9.
- ^ Paul, Burton (1979). Kinematics and dynamics of planar machinery (illustrated ed.). Prentice-Hall. ISBN 978-0-13-516062-6.
- ^ Rorres, Chris (2017). Archimedes in the 21st Century. Springer International Publishing. p. 71. ISBN 9783319580593.