Pulley
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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.
Pulleys on a ship. In this context, pulleys are normally known as blocks
Pulley in oil derrick
A hoist using the compound pulley system yielding an advantage of 4. The single fixed pulley is installed on the hoist. The two movable pulleys (joined) are attached to the hook. One end of the rope is attached to the crane frame, another to the winch.
A double tackle has dual pulleys in both the fixed and moving blocks with four rope parts supporting the load W.
Block and tackle
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A block and tackle, purchase, or only tackle is a system of two or more pulleys with a rope or cable threaded between them, used to provide tension and lift heavy loads.
Pulley
…Roman Egypt, Hero of Alexandria (c. 10–70 AD) identified the pulley as one of six simple machines used to lift weights. 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…
A gun tackle has a single pulley in both the fixed and moving blocks with 2 rope parts (n) supporting the load (FB) of 100 N. The mechanical advantage is 2, requiring a force of only 50 N to lift the load.
Three vintage snatch blocks showing the "snatch" closed, opened, and securely moused