1300 in the sense of 'a wheel having teeth or cogs late 14c., 'tooth on a wheel' cog-wheel, early 15c. From Middle English cogge, from Old Norse (compare Norwegian kugg ('cog'), Swedish kugg, kugge ('cog, tooth')), from Proto-Germanic * kuggЕЌ (compare Dutch kogge (' cogboat'), German Kock), from Proto-Indo-European * gugДЃ ('hump, ball') (compare Lithuanian gugГ ('pommel, hump, hill'), from PIE * gД“w- ('to bend, arch'). The wooden cogs are held in place by nails.ДЄ cog is a tooth on a wheel. ДЄ cast gearwheel (above) meshing with a cogged mortise wheel (below).

In this context, the meaning of 'toothed wheel in machinery' first attested 1520s specific mechanical sense of 'parts by which a motor communicates motion' is from 1814 specifically of a vehicle (bicycle, automobile, etc.) by 1888. The word gear is probably from Old Norse gГёrvi (plural gГёrvar) 'apparel, gear,' related to gГёra, gГёrva 'to make, construct, build set in order, prepare,' a common verb in Old Norse, 'used in a wide range of situations from writing a book to dressing meat'.

In nature: in the hind legs of the nymphs of the planthopper insect Issus coleoptratus.

200вЂ“265 CE: Ma Jun used gears as part of a south-pointing chariot. It could predict the movement and position of the sun, moon and planets decades in advance and could solve different astronomical problems.

2nd century BC: The Antikythera mechanism, the world's oldest analog computer is built.

725 CE: The first geared mechanical clocks were built in China.

6th century CE: A geared calendrical device showing the phase of the Moon, the day of the month and the Zodiac was invented in the Byzantine empire. 1221 CE The geared astrolabe was built in Isfahan showing the position of the moon in the zodiac and its phase, and the number of days since new moon. 13thвЂ“14th centuries: The worm gear was invented as part of a roller cotton gin in the Indian subcontinent. The Astrarium had seven faces and 107 moving parts it showed the positions of the sun, the moon and the five planets then known, as well as religious feast days.

The Astrarium of Giovanni Dondi dell'Orologio was a complex astronomical clock built between 13 by Giovanni Dondi dell'Orologio.1386 CE: The Salisbury Cathedral clock: it is the world's oldest still working geared mechanical clock.Differential gears may have been used in some of the Chinese south-pointing chariots, but the first verifiable use of differential gears was by the British clock maker Joseph Williamson in 1720.Д®xamples of early gear applications include: The worm gear was invented in the Indian subcontinent, for use in roller cotton gins, some time during the 13thвЂ“14th centuries. See Rack and Pinion for an example.ДЄ complex geared calendrical device showing the phase of the Moon, the day of the month and the places of the Sun and the Moon in the Zodiac was invented in the Byzantine empire in the early 6th century CE. ДЇurthermore, a gear can mesh with a linear toothed part, called a rack, producing movement in a straight line instead of rotation (movement in a circle). Sometimes a CVT is referred to as an 'infinitely variable transmission'. The term describes similar devices, even when the gear ratio is continuous rather than discrete, or when the device does not actually contain gears, as in a CVT. In transmissions with multiple gear ratios-such as bicycles, motorcycles, and cars-the term 'gear' (e.g., 'first gear') refers to a gear ratio rather than an actual physical gear. An advantage of gears is that the teeth of a gear prevent slippage. The gears in a transmission are analogous to the wheels in a crossed, belt pulley system. Two or more meshing gears, working in a sequence, are called a gear train or a transmission.

The teeth on the two meshing gears all have the same shape.

The rotational speeds, and the torques, of two meshing gears differ in proportion to their diameters. Gears of different sizes produce a change in torque, creating a mechanical advantage, through their gear ratio, and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source. A gear may also be known informally as a cog. The basic principle behind the operation of gears is analogous to the basic principle of levers. Oil mill in Storkensohn ( Haut-Rhin), France.ДЄ gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called cogs), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. Cast iron mortise wheel with wooden cogs (powered by an external water wheel) meshing with a cast iron gear wheel, connected to a pulley with drive belt.

Gear vs cog