What Is a Fixed Pulley?

B. Turner

Pulleys consist of a rope or wire wrapped around a wheel or drum. They are one of the oldest and most basic types of machines, and have played an important role in lifting and and hoisting operations for centuries. One of the most common types of pulleys is the fixed pulley, which consists of a drum with a fixed axle. As the user operates the device, the rope or wire moves while the pulley remains stationary. The fixed pulley is the opposite of a movable pulley, in which the drum moves up and down along with the rope or wire.

A simple fixed pulley.
A simple fixed pulley.

A fixed pulley is designed to help users lift heavy loads with less effort, or to simply change the direction of the force required for lifting. For example, a user attempting to hoist a box up onto a high shelf will find it much easier to pull the box up using a rope rather than pushing it up from underneath. A fixed pulley extended from the ceiling or the shelf would allow the user to change the direction of force from pushing up to pulling down, resulting in a perceived decrease in effort. By changing the direction of the force, this pulley design can also be used to operate machinery, such as a conveyor belt or other equipment.

Several wooden pulleys on a boat.
Several wooden pulleys on a boat.

The most important thing to understand about the fixed pulley is that it doesn't actually reduce the required level of force required to lift a load. Even with this pulley in place, the lifting force remains exactly equal to the force generated by the load itself. This results in a mechanical advantage of one, which means that the lifting and load forces are the same. It also means that users do not gain any mechanical advantage by using the pulley, but simply perceive that they do.

A movable pulley, on the other hand, offers a mechanical advantage of two. This means that users must apply only half as much force as that generated by the load in order to lift this load successfully. The effort of lifting appears easier, and in actuality, it is easier. Compound pulleys, which incorporate more than one fixed or movable drum in a single pulley design, can increase mechanical advantage even further.

A fixed pulley can be a simple yet effective tool in almost any basic lifting or hoisting operation. These pulleys are found on oil rigs and well-drilling equipment, as well as many cranes. They also are an important part of an aircraft's operating mechanism, and can be found in a variety of engines and machines.

Automobile engines typically use pulley systems, such as those that work with the alternator, fans, water pumps, and timing gears.
Automobile engines typically use pulley systems, such as those that work with the alternator, fans, water pumps, and timing gears.

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