Plural of gearbox; mechanical devices that transmit power and change the speed or direction of rotating machinery.
From 'gear' (a toothed wheel) and 'box' (a container). The term emerged in the late 19th century as automobiles and machinery required systems to control rotational force.
Without gearboxes, cars would be stuck in one speed forever—they're the invisible engineers that let your engine's power work efficiently whether you're accelerating from a standstill or cruising on the highway.
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