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Pulley facts for kids

Kids Encyclopedia Facts
Diagram of a fixed pulley (brown) that can raise or lower a weight (dark gray) using a rope (light gray)
Movable pulley

A pulley is a simple machine that is used to lift heavy objects. Block and tackle system is a modified form of a pulley. Pulleys are usually used in sets designed to make the amount of force needed to lift something smaller. A pulley may be simple, but this is used in complex things like elevators! Pulleys are also useful in construction sites.

Types of pulleys

  • Static A static or class 1 pulley has an axle that is "staticed" or is stationary, meaning that it cannot be moved. A fixed pulley is used to redirect the force in a rope (called a belt when it goes in a full circle). A fixed pulley has a mechanical advantage of 1. The static pulley has a wheel and an axle.
  • Movable A movable or class 2 pulley has an axle that is "free" to move in space. A movable pulley is used to transform forces. A movable pulley has a mechanical advantage of 2. That is, if one end of the rope is anchored, pulling on the other end of the rope will apply a doubled force to the objecT attached to the pulley.
  • Compound A compound pulley is a combination fixed and movable pulley system.
    • Block and tackle - A block and tackle is a compound pulley where several pulleys are mounted on each axle, further increasing the mechanical advantage.

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 BCE) and Mesopotamia in the early 2nd millennium BCE. In Roman Egypt, Hero of Alexandria (c. 10-70 CE) identified the pulley as one of six simple machines used to lift weights. Plutarch reported that Archimedes moved an entire warship, laden with men, using compound pulleys and his own strength.

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See also

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