Home › Engineering & Industrial Design › Mechanical Systems & Kinematics › gear

gear

GEER /ɡɪər/

nounverbA2SATACTTOEFL

GeneralTechnical

A toothed wheel that fits into another toothed wheel to change the speed or direction of transmitted motion.

A gear is a specific, fundamental mechanical component. Unlike a pulley (which uses a smooth belt), a gear uses teeth to ensure a positive, non-slip connection. Gears are used in groups (gear trains) to multiply torque or increase speed.

The story behind the word. The word gear originally had nothing to do with machinery. In Old Norse, 'gervi' meant 'equipment', 'armor', or 'apparel'. In Middle English, it referred to a knight's battle gear or a horse's harness. As machinery developed, the term was transferred to describe the essential 'equipment' of a machine—specifically, the toothed wheels that made it run.

Word relationships

cogwheel: Cogwheel is a more traditional or informal term for a gear, whereas 'gear' is the standard engineering term.

pulley: A pulley is a smooth wheel that transmits motion via a belt, relying on friction rather than interlocking teeth.

Commonly confused with

sprocket: A sprocket is a toothed wheel that meshes with a chain (like on a bicycle), whereas a gear meshes directly with another toothed wheel.

Word family

gearing (noun): The arrangement or ratio of gears in a machine.
gearless (adjective): Operating without gears.

Collocations

spur gear
bevel gear
gear ratio
gear train

Idioms & expressions

shift gears
get into gear

Example sentences

"The watchmaker carefully placed the tiny brass gear into the escapement mechanism." A description of a mechanical watch
"Shift into a lower gear before you start climbing the hill to keep your pedaling cadence steady." A cycling guide explaining mountain riding

Memory hook

Think of your 'gear' (equipment) for an outdoor trip. A machine's 'gears' are its essential equipment for moving. Gears are the teeth of the machine.

When not to use

Do not use gear to describe a smooth wheel or roller; gears must have teeth (cogs).

Fun facts

The oldest known gears are found in the Antikythera mechanism, dating back to around 150-100 BC.
Nature actually invented gears first: the nymph of the Issus planthopper insect has interlocking gear teeth on its hind legs to synchronize its jumps.