Pulley
From Wikipedia, the free encyclopedia.

A pulley is a wheel with a groove along its edge, for holding a rope or cable.

Types of Pulleys

• A fixed pulley has a fixed axle and is used to redirect the rope (called a belt when it goes in a full circle).
  • A fixed pulley has a mechanical advantage of 1.

• A movable pulley has a free axle, and is used to transform forces - when stationary the total force on the axle balances the total force provided by the tension in the rope (which is constant in magnitude in each segment).
  • A movable pulley has a mechanical advantage of 2.

So, for instance, if one end of the rope is attached to a fixed object, pulling on the other end will apply a doubled force to any object attached to the axle. This can be increased by using a block and tackle, where there are several pulleys on each axle. Pulleys are usually counted as one of the simple machines.

Plutarch reported that Archimedes moved an entire warship, laden with men, using compound pulleys and his own strength.

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Pulley Images

Early Pulleys

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Single Fixed Pulley

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Single Movable Pulley

The original article can be found at: http://en.wikipedia.org/wiki/Pulley.
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