Gears or cogwheels are integral components of any rotating machine that allow for the change in speed, torque or direction of any power source. They are one of the fundamental mechanical engineering innovations in history.
Any change in torque with the use of gears and cogwheels necessarily creates a mechanical advantage thanks to the phenomenon of the gear ratio.
A gear can mesh with a linear toothed part, called a rack, producing translation instead of rotation.
It is unclear exactly when gears and cogwheels were first invented but some credit Archimedes. Today, gears are present in many moving systems and machines from bicycles to ship engines.