Gear

A gear, or gearwheel, is a rotating machine part with teeth that mesh with another toothed part to transmit rotational motion and torque between shafts. Gears were developed independently in more than one ancient civilization rather than by a single inventor: the earliest surviving physical gears come from Warring States-period China in the 4th century BC, while in Greece Aristotle described geared windlasses around 330 BC and the sophisticated Antikythera mechanism used gearing to calculate astronomical positions in the 2nd or 1st century BC. Centuries later the Chinese engineer Ma Jun used differential gearing in a south-pointing chariot, showing the technology continued to develop independently in East Asia as well.