What Is the Mechanical Advantage of Single Movable Pulleys?

By Chris Burke; Updated April 25, 2017

Pulleys are one of six types of simple machines, a device that allows people to accomplish work with less effort than the task would otherwise require. Simple machines allow this to happen due to their mechanical advantage, which provides a multiplier effect on the effort exerted. A moveable pulley is a type of pulley that moves with the object being moved.

Mechanical advantage is the name given to the force multiplier given by a simple machine. A machine’s mechanical advantage is essentially a measure of how much the required force is spread throughout the machine. Mechanical is a force multiplier because it multiplies the amount of effort you exert. For example, if a box required 100 newtons of force to move it, and you attached it to a pulley with a mechanical advantage of 3, you would only need to apply 33 newtons of force, because 33 times 3 equals 99, which is close enough to 100.

Pulley

All pulleys have two components: a rope and a grooved wheel. The rope fits around the wheel, allowing the rope to move around it. Pulleys are either fixed or moveable. A fixed pulley is stationary, attached to a wall or similar object. The weight moved by the pulley is attached to the rope. The wheel of a moveable pulley is not attached to any stationary object; one end of the rope is stationary instead. In a moveable pulley, the weight is attached to the wheel rather than the rope, and the wheel moves along the length of the rope as the weight is lifted or lowered.

Moveable Pulley

The mechanical advantage of a moveable pulley is 2. This means that a moveable pulley will halve the required force needed to move any object attached to it. This occurs because in a moveable pulley one end of the rope is stationary, which means it absorbs some of the force needed to move the object. So, if you attach a 100 newton box to a moveable pulley, you will only need to apply 50 newtons of force to move the box because the moveable pulley will multiply your force by 2.