What is the primary purpose of a pulley in simple machines?

The primary purpose of a pulley in simple machines is to change the direction of the force applied. When a pulley is used, it allows a user to lift a load by pulling down on a rope, which directs the force horizontally or vertically depending on how the pulley is configured. This can make lifting heavy objects easier, as it allows for the force to be applied in a direction that is more convenient or manageable.

For example, when using a fixed pulley, the effort applied downward through the rope translates into an upward force that lifts the load. This change in direction can reduce strain on the user and improve efficiency when lifting loads over vertical distances. In essence, a pulley does not inherently create or increase force by itself but instead modifies the direction in which force needs to be applied, thus making it a valuable tool in mechanical systems.