# Pulley

## What is a pulley?

A pulley is a wheel with a grooved rim around which a cord passes. It acts to change the direction of a force applied to the cord and is chiefly used (typically in combination) to raise heavy weights.

## How does it provide mechanical advantage?

The greater the number of pulleys in the system, the less force it will take to lift an object. The pulley makes lifting the boulder easier because it reduces the effort required to lift. But notice that, although lifting becomes easier, you pull a rope that travels a greater distance than the height to which you lift the boulder. This extra distance decreases your effort by giving you a mechanical advantage. The mechanical advantage of a moveable pulley is equal to the number of ropes that support the moveable pulley.

## Examples

1. Identify the fulcrum. This will be the point about which the the board or rigid object pivots around.

2. Identify the locations of the input and output forces. The input force is the force that is applied to the lever, oftentimes by a machine or human. The output force is the force that the lever exerts onto an object.

3. Find the distance between the fulcrum and the input force. This is known as the resistance arm.

4. Find the distance from the fulcrum to the output force. This is known as the effort arm.

5. Divide the length of the effort arm by the length of the resistance arm to calculate mechanical advantage.

6. MA = L (effort arm) / L(resistance arm)

Suppose that a pulley system, you need to exert a force of 1,400 N to lift a heavy object. But without the pulley system, you need to exert 4,200 N to lift the object. What is the mechanical advantage of the pulley system?

MA= 3