Gear

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Animation of two spur gears in motion

A gear is a rotating machine part having cut teeth or, in the case of a cogwheel, inserted teeth (called cogs), which mesh with another toothed part to transmit torque. Geared devices can change the speed, torque, and direction of a power source. Gears almost always produce a change in torque, creating a mechanical advantage, through their gear ratio, and thus may be considered a simple machine.

History

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Ancient Han iron gears

The concept of gears dates back to ancient times. The earliest known gears were used by the Greeks in the Antikythera mechanism, an ancient analog computer. Gears were also used in ancient China, as evidenced by the South-pointing chariot, a device that used a differential gear system to maintain a constant direction.

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The Antikythera mechanism, an ancient Greek analog computer

Types of Gears

Gears come in several types, each serving different purposes and applications:

Spur Gears

Spur gears are the most common type of gears. They have straight teeth and are mounted on parallel shafts. Spur gears are used in a wide range of applications, from clocks to industrial machinery.

Helical Gears

Helical gears have teeth that are cut at an angle to the face of the gear. This allows for more gradual engagement of the teeth, resulting in smoother and quieter operation compared to spur gears.

Bevel Gears

Bevel gears are used to transmit power between shafts that are at an angle to each other. They are commonly used in differential drives, which can transmit power to two axles spinning at different speeds, such as those on a car.

Worm Gears

Worm gears are used to transmit power between non-parallel, non-intersecting shafts. They provide a high reduction ratio and are used in applications where space is limited.

Rack and Pinion

A rack and pinion is a type of linear actuator that comprises a pair of gears that convert rotational motion into linear motion. It is commonly used in steering systems of cars.

Applications

Gears are used in a wide variety of mechanical devices. They are used in everything from clocks to bicycles to industrial machinery. Gears are essential components in the automotive industry, where they are used in transmissions and differentials.

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Model of a South-pointing chariot, an ancient Chinese device using differential gears

Mechanical Advantage

The mechanical advantage of a gear system is determined by the gear ratio, which is the ratio of the number of teeth on the output gear to the number of teeth on the input gear. This ratio determines the torque and speed of the output gear relative to the input gear.

Related Pages

• Simple machine
• Torque
• Transmission (mechanics)
• Differential (mechanical device)

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Cog wheel and stone spindle

See Also

• Pulley
• Lever
• Wheel and axle