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gear, toothed wheel, cylinder, or cone that transmits motion from one part of a machine to another; it is one of the oldest means of transmitting motion. When the teeth of two gears are meshed, turning one gear will cause the other to rotate. In most cases both gears are mounted on shafts so that when one shaft turns, the other also rotates. By meshing two gears of different diameters, a variation in both speed and torque between the two shafts is obtained; the smaller gear in this case is called the pinion. A spur gear consists of a wheel with straight teeth mounted radially either on the inner circumference (internal spur gear) or outer circumference (external spur gear) of the wheel. Two meshed spur gears are used to transmit motion between parallel shafts. A rack and pinion consists of a pinion engaging and transferring motion to or from a special kind of spur gear, called a rack, consisting of a series of teeth in a straight line on a flat surface. The rack and pinion changes linear motion into rotary motion, or vice versa. A helical gear is similar to a spur gear, but its teeth are twisted instead of straight. Helical gears can be used to transmit motion between shafts that do not intersect and are at any angle with respect to each other. A bevel gear has straight or curved teeth on a conical surface near its rim. Bevel gears are used to transmit rotary motion between shafts that are not parallel and that would intersect at an angle if extended. Hypoid gears are special bevel gears used in the differential of an automobile to connect the drive shaft to the rear axle. A worm gear, meshed with a threaded cylinder, or worm, that resembles a screw, is used to transmit motion between perpendicular, nonintersecting shafts. See transmission.


See D. W. Dudley, ed., Gear Handbook (1962); H. J. Watson, Modern Gear Production (1970); R. J. Drago, Fundamentals of Gear Design (1988).

The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



the main part of a gear drive, in the form of a disk with teeth on a cylindrical or conical surface engaging the teeth of another gear. Spur gears can have external or internal teeth. The teeth can be spur, helical, double helical (angular), or curvilinear. The most common tooth shape is invo-lute; less often it is cycloid or some other form. Gears are also called pinions. In reduction gears, for example, the small driving wheel is customarily called a pinion regardless of the number of teeth, and the large driven wheel is called a gear. Often all gears are called pinions. The design of a gear de-pends on its purpose, size, and means of manufacture.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


(design engineering)
A toothed machine element used to transmit motion between rotating shafts when the center distance of the shafts is not too large.
(mechanical engineering)
A mechanism performing a specific function in a machine.
An adjustment device of the transmission in a motor vehicle which determines mechanical advantage, relative speed, and direction of travel.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


A machine element used to transmit motion between rotating shafts when the center distance of the shafts is not too large. Toothed gears provide a positive drive, maintaining exact velocity ratios between driving and driven shafts, a factor that may be lacking in the case of friction gearing which is subject to slippage.

The application of gears for power transmission between shafts falls into three general categories: those with parallel shafts, those for shafts with intersecting axes, and those whose shafts are neither parallel nor intersecting but skew.

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.


1. a toothed wheel that engages with another toothed wheel or with a rack in order to change the speed or direction of transmitted motion
2. a mechanism for transmitting motion by gears, esp for a specific purpose
3. the engagement or specific ratio of a system of gears
4. Nautical all equipment or appurtenances belonging to a certain vessel, sailor, etc.
5. short for landing gear
6. a less common word for harness
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

Samsung Gear

(1) For the Samsung smartwatch with a built-in phone, see Samsung Gear S.

(2) The Gear is a smartwatch from Samsung. Debuting in 2013 as the "Galaxy" Gear and renamed Samsung Gear in its second generation, the watch is not a stand-alone device. The Gear communicates back and forth with Android smartphones that have Android Version 4.3 (Jelly Bean) and higher. However, the first two generations work only on selected Samsung Galaxy models, whereas the third-generation Gear Live works with all Android hardware.

With a 1.6" screen and 4GB of storage, the operating system in the watch changed in each of four generations, from Android to Tizen to Android Wear, and back to Tizen. The watch is controlled by the Gear Manager app in the phone, and via touch or voice, users make and answer phone calls, view notifications, control their music, check weather, set alarms and create calendar entries. See Tizen and Android Wear.

Gear 2, Neo, Fit and Live
Introduced in 2014, the second-generation Gear 2 moved the camera lens from the band to the body of the watch. The Gear 2 Neo is a camera-less plastic unit, and the Fit is a sports model. Starting with the second-generation, Gears are dust proof, water resistant and include a heart rate monitor.

In 2014, the third-generation Gear Live dropped the cameras altogether as well as the stand-alone music player in the Gear 2. The Android Wear operating system significantly changed the user interface with its Google Now notification system. Like the Gear 2, the Gear Live supports multiple watch faces, but the Gear Live can also run in a dimmed mode to keep the time always displayed (see Android Wear). See Samsung Gear S, Samsung Gear VR, smartwatch and Android.

The Original Gear
The camera lens on the first Gear smartwatch was on the band. It was moved to the watch body on the Gear 2.

The Original Gear
The camera lens on the first Gear smartwatch was on the band. It was moved to the watch body on the Gear 2.

Gear and Gear Live
A major change from the original (left), the third-generation Gear Live (right) eliminated the phone dialer and camera altogether.
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References in periodicals archive ?
Design features include the time it takes to retract the landing gear. This corresponds to aircraft performance considerations as in a climb over an obstacle in a specific distance, and associated single-engine climb performance for multi-engine aircraft.
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Technical aspects, is analyzed to determine the effectiveness of the fishing gear used, include: size of the boat or ship ([X.sub.1]), fuel consumption per day ([X.sub.2]), use of fishing gear ([X.sub.3]), material fishing gear and production of catch per day ([X.sub.4]).
The coupled three-dimensional (transverse-rotational-axial) model must be general so that a PGT with any number of planets can be analyzed, in which the planets can be spaced equally or unequally around the sun gear at any phasing relationship, and the sun and ring gear and carrier can be floating in the radial direction.
I placed the landing gear handle to the down position, but the result was not what we had anticipated.
Precision Gear Holdings, which has a workforce of around 190, generates net sales of some USD45m (EUR32.7m) per year.
However, each planet gear is actually a compound design which meshes with two sun pinion shafts: one input shaft and one output shaft.
The company's other popular item is the PG-series planetary gear reducer featuring high positioning accuracy, high torque, low backlash, low noise and high efficiency, and high compatibility with most servo motors.
The turbo units with power ratings from 700 kW to 10000 kW with gear drivers are experimentally tested in situ using bearing housings absolute vibration parameters measured with seismic transducers--pjezoaccelerometers.