Pulley
Pulley
Poltergeist
<catset>Category="Mechanics"</catset>[image]A <b>pulley</b> is a <a href="Wheel">Wheel</a> with a groove along its edge, for holding a <a href="Rope">Rope</a> or <a href="Cable">Cable</a>. Pulleys are usually used in sets designed to reduce the amount of force needed to lift a load. However, the same amount of work is necessary for the load to reach the same height as it would without the pulleys. The <a href="Magnitude (mathematics)">magnitude</a> of the force is reduced, but it must act through a longer distance. Pulleys are one of the six <a href="Simple machine">simple machines</a>.<h2 style="margin: 0; padding-top: 0.5em; padding-bottom: 0.17em; border-bottom: 1px solid #aaaaaa; font-size: 150%;">Types of Pulleys</h2>A <i>fixed</i> or <i>class 1</i> pulley has a fixed <a href="Axle">Axle</a> and is used to redirect the force in a rope (called a <a href="Belt (mechanical)">belt</a> when it goes in a full circle). A fixed pulley has a <a href="Mechanical advantage">Mechanical advantage</a> of 1.<p>A <i>movable</i> or <i>class 2</i> pulley has a free axle and is used to transform forces. A movable pulley has a mechanical advantage of 2. That is, if one end of the rope is attached to the fixed object, pulling on the other end of the rope will apply a doubled force to the object attached to the axle.<p>A <i>compound pulley</i> is a combination fixed and movable pulley system.<p>A <i><a href="Block and tackle">Block and tackle</a></i> is a compound pulley where several pulleys are mounted on each axle, further increasing the mechanical advantage. <a href="Plutarch">Plutarch</a> reported that <a href="Archimedes">Archimedes</a> moved an entire warship, laden with men, using compound pulleys and his own strength.