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 the 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 "geared":
... improvements in detail design and the application of more modern locomotive technology to the geared locomotive Lima (manufacturers of the Shay) were dragging ... Aveling and Porter built some geared locomotives which were, essentially, traction engines with flanged wheels ... Avonside Engine Company produced a small number of narrow gauge geared steam locomotives for sugar cane plantations in Natal ...
... More recently, quantum physics uses "quantum gears" in their model ... A group of gears can serve as a model for several different systems, such as an artificially constructed nanomechanical device or a group of ring molecules ...
... The geared turbofan is a type of turbofan airplane engine, similar to a turbojet ... It consists of a geared ducted fan with a smaller diameter turbojet engine mounted behind it that powers the fan ...
... bass and guitar family instruments are usually geared, and are called tuning machines or machine heads ... Geared pegs for violin family instruments also exist, although they have not gained wide use ...
Famous quotes containing the word geared:
“In early days, I tried not to give librarians any trouble, which was where I made my primary mistake. Librarians like to be given trouble; they exist for it, they are geared to it. For the location of a mislaid volume, an uncatalogued item, your good librarian has a ferrets nose. Give her a scent and she jumps the leash, her eye bright with battle.”
—Catherine Drinker Bowen (18971973)