An inclined plane makes work easier by allowing the work to be done over a longer distance. So does a screw! The closer together the threads of a screw are, the longer the distance over which the effort is exerted, and the more the force is multiplied.

Examples of a screw include the lid of your jar of peanut butter, the jack you lift the car with when changing a tire, and airplane propellers.

Screws are designed to change the direction of effort. The screw's threads move objects up or down as the screw turns. When you turn a screw into a piece of wood in a circle with a screwdriver the screw goes down into the wood. Circular motion is turned into forward motion. This is how a fan creates a current of air to cool you off on a hot day. The blades of your fan are also a type of screw.

When designing a motion machine screws can be used in many ways. To fasten objects together, to push or pull objects, or to raise or lower heavy objects.