The Pulley

By, Olivia Duke

What is a Pulley?A pulley is a simple machine used to change the

direction of an applied force. It is the basis of a lot of modern machinery. A pulley is a wheel with a groove that runs around it. A rope, belt, or cable runs through the groove. The pulley could be used like this, or connected with others in the pulley system. The more pulleys used, the less force needed. An example of a pulley is a flagpole. A pulley is used to put the flag up and to take it down.

The Original Pulleys

People in Mesopotamia were using pulleys as early as 1500 B.C. The first compound pulleys were invented by the Archimedes of Syracuse in 287-212 B.C. An entire warship, heavy with men, was moved by Plutarch using compound pulleys and his own strength. The pulley’s original use was to lift buckets of water. An interesting fact about the pulley: it was used in Ancient Greek plays to lower a god or goddess on stage.

The Different Types of PulleysThe fixed or class one pulley: This type of pulley has an axle that is “fixed” or anchored in place. It is used to change the direction of the force on the rope, or the belt. It also has a mechanical advantage of one, which means the force is equal on both sides.

The movable or class two pulley: This type of pulley has a free axle, or an axle that is “free” to move in space. It is used to multiply forces. It also has a mechanical advantage of two, which means if one end of the rope is anchored pulling on the other end of the rope will apply double the force on the object connected to it.

A compound pulley is a combination of each.

Block and tackle: A pulley in which several different pulleys are connected to each axle, which increases the mechanical advantage.

Sources

http://www.machine-history.com/node/309

http://www.wisegeek.org/what-is-a-pulley.htm

http://examples.yourdictionary.com/examples/pulley-examples.html

http://ed101.bu.edu/StudentDoc/Archives/ED101sp06/cjhpyo/Pulley.html