A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source. The most common situation is for a gear to mesh with another gear, however a gear can also mesh with a non-rotating toothed part, called a rack, thereby producing translation instead of rotation.
The gears in a transmission are analogous to the wheels in a pulley. An advantage of gears is that the teeth of a gear prevent slipping.
When two gears of unequal number of teeth are combined a mechanical advantage is produced, with both the rotational speeds and the torques of the two gears differing in a simple relationship.
In transmissions which offer multiple gear ratios, such as bicycles and cars, the term gear, as in first gear, refers to a gear ratio rather than an actual physical gear. The term is used to describe similar devices even when gear ratio is continuous rather than discrete, or when the device does not actually contain any gears, as in a continuously variable transmission.
The earliest known reference to gears was circa A.D. 50 by Hero of Alexandria, but they can be traced back to the Greek mechanics of the Alexandrian school in the 3rd century B.C. and were greatly developed by the Greek polymath Archimedes (287–212 B.C.). The Antikythera mechanism is an example of a very early and intricate geared device, designed to calculate astronomical positions. Its time of construction is now estimated between 150 and 100 BC.
Other articles related to "gear, gears":
... A pinion is a round gear used in several applications usually the smallest gear in a gear drive train, although in the case of John Blenkinsop's Salamanca, the pinion was rather large ... In many cases, such as remote controlled toys, the pinion is also the drive gear ... the smaller gear that drives in a 90-degree angle towards a crown gear in a differential drive ...
... Gear is a six-issue comic book limited series written and illustrated by Doug TenNapel ... Gear featured black-and-white artwork mostly created with an ink brush by TenNapel ...
... Unlike with ordinary gear trains, the direction of transmission (input shaft vs output shaft) is not reversible when using large reduction ratios, due to the greater friction involved between the worm and worm-wheel ... is used then the ratio reduces accordingly and the braking effect of a worm and worm-gear may need to be discounted as the gear may be able to drive the worm ... Worm gear configurations in which the gear cannot drive the worm are said to be self-locking ...
... Modern physics adopted the gear model in different ways ... Maxwell used a gear wheel and called it an "idle wheel" to explain the electrical current as a rotation of particles in opposite directions to that of the rotating field lines ... More recently, quantum physics uses "quantum gears" in their model ...
... Heavy Gear Fighter is a stand-alone two-player card game set in the Heavy Gear universe ...
Famous quotes containing the word gear:
“For women ... bras, panties, bathing suits, and other stereotypical gear are visual reminders of a commercial, idealized feminine image that our real and diverse female bodies cant possibly fit. Without these visual references, each individual womans body demands to be accepted on its own terms. We stop being comparatives. We begin to be unique.”
—Gloria Steinem (b. 1934)
“But Lord, remember me and mine
Wi mercies temporal and divine!
That I for grace and gear may shine,
Excelled by nane!
And a the glory shall be thine!
—Robert Burns (17591796)