Gears are used to both change rotational speed and direction of force. Gears are toothed wheels that mesh together and transmit rotational motion and force between them. They have different sizes and numbers of teeth, which allows them to change the speed and direction of rotation.

When two gears of different sizes are meshed together, the gear with fewer teeth (smaller gear) will rotate faster than the gear with more teeth (larger gear). This change in rotational speed is used to transmit power and control the speed of different components in machinery.

Additionally, gears can change the direction of force. When two meshed gears have their teeth arranged in such a way that they rotate in opposite directions, the force and motion are redirected. For example, a pair of meshed gears can change the direction of rotation from horizontal to vertical or vice versa.