A pulley is a simple machine that makes it easier to lift objects, by requiring less input force. Learn about the mechanical advantage of pulleys, and how to calculate the mechanical advantage, based on the number of rope sections in the pulley system.
Pulleys are simple machines made of a rope or cable and a grooved wheel.
With a pulley, the user pulls one end of the rope and the other end of the rope pulls up on the object you want to move.
The force produced by the user of the pulley is called the input force and the force pulling up on the object is called the output force.
Pulleys provide different amounts of mechanical advantage based on the type of pulley being used. Mechanical advantage is the number of times a machine increases the force exerted on it.
A fixed pulley has a mechanical advantage of one, however, it is able to change the direction of force on an object.
A movable pulley has a mechanical advantage of two and is connected to the object being moved.
A block and tackle pulley provides a mechanical advantage of three and is made up of fixed and movable pulleys.
Calculating the mechanical advantage of a pulley:
The mechanical advantage of a pulley is equal to the number of rope sections in the system (not counting the rope that is traveling to the effort).
This image is a drawing of a fixed pulley with a mechanical advantage of one.