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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.
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.
Pulleys are useful in construction sites.