What is Gear?- Definition, Principle, And Types of Gear.

By Aina Parasher|Updated : May 9th, 2022

A gear is a toothed cylindrical or roller-shaped element of a machine that meshes with another toothed cylindrical element to transmit power from one shaft to another. It is primarily used to obtain different torque and speed ratios or to change the direction of the driving shaft and driven shaft.

"Gears are ordinary, rotating parts of the machine that usually have teeth." When they connect to other gears, they transmit torque. That is sort of a twisting force. 

There are several other power transmission tools like belt drives, chain drives, rope drives, etc., but the main advantage of the gear system is that there is almost negligible or no slippage between the driving and driven member. Gears are primarily used wherever there's a short distance between the axis driving and driven shaft, like a bicycle, motorcycle, car, etc.

Table of Content

What is the Principle of Gears?

It works on the fundamental principle of thermodynamics, the law of conservation, or the first law of thermodynamics. which states that energy can neither be created nor destroyed, we can say it is conservative. It can be transformed from one form to another. We know that power is the function of torque (force in rotary motion) and speed (P = TV) of the shaft. Therefore, when we connect a small gear on the driving shaft and a larger gear on the driven shaft, the driven shaft speed decreases per unit rotation of the driving shaft.

As we know, power is conservative, so according to this, the torque of the driven shaft increases according to the ratio of driving gear to driven gear, or we can say, according to the ratio of driving shaft velocity to driven shaft velocity. Therefore, by using various sizes of gears, we can obtain various combinations of torque and speed of the driven member.

What are the Types of Gears?

There are plenty of ways in which we can classify the gears, such as according to the construction of teeth, use, the direction of motion transfer, etc. However, primary gears are classified according to the design of teeth. The most common types of gears along with their applications are enlisted in the below table.

Type of Gear


Spur Gear


Electric Screwdrivers


Watering Systems

Power Plant Machinery

Helical Gear





Bevel Gear


Marine Applications


Railway Track Inspection Machines

Rack and Pinion

Steering Mechanism

Lifting Mechanism (Vertical Movement)

Positioning Mechanisms


Worm Gear

Packaging Equipment

Worm Drive Speed Reducers

Spur Gear

These gears are used to transfer power in the same plane as when the driving and driven shafts are parallel to each other. In this type of gear, the teeth are parallel to the axis of the shafts, so when it meshes with another spur gear, it transmits the power in a parallel shaft, and when it connects with the helical gear, it will transmit power at an angle from the driving axis.

Helical Gear

Teeth on helical gears are cut at a 45-degree angle to the axis. It has helicoid teeth on a cylindrical roller. Helical gears have the advantage of producing less noise and vibration than spur gears since the load is dispersed across the entire helix. They are also commonly used in industries since they are less prone to wear and tear. It's also used to transmit power in parallel shafts, but it's also used in non-parallel shafts on occasion. In helical gears, if the pinion (driving gear) is cut with right-handed teeth, the gear (driven gear) is cut in the opposite direction with left-handed teeth.

Double Helical or Herringbone Gear

This gear has both right and left-handed teeth on one gear. Power is transmitted between parallel shafts using the double-helical gear, often known as the herringbone gear. It was created to offset the drawback of single-helical gears' high-end thrust.

Bevel Gear

A bevel gear is a toothed rotating mechanical device that transfers mechanical energy or shaft power between shafts that cross at an angle or perpendicularly. As a result, the shaft power's axis of rotation changes. Apart from this, bevel gears can also increase or decrease torque while causing the angular speed to change in the opposite direction.

Rack and Pinion Gear

In automotive steering systems, this gear is used. In this sort of gear, teeth are cut on a rack with a straight rectilinear shape, and a pinion is one spur gear. This is the process of converting rotary motion into linear motion. It is referred to as the infinite radius driven gear.

Worm Gear

This gear transmits power to a shaft that does not intersect and is at an angle. In this design, the driving gear is a screw gear, while the driven gear is a spiral-toothed helical gear.

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  • A gear is a rotating circular machine part with cut teeth, or inserted teeth (called cogs) in the case of a cogwheel or gearwheel, which mesh with another toothed part to convey torque. Gear is sometimes called as a cog. The teeth of a gear prevent slippage, which is an advantage.

  • Spur gears are mechanical devices that transport motion and power from one shaft to another through a succession of mated gears, increasing or decreasing the speed of a device or multiplying torque.

  • The spur gears have the following disadvantages.

    • These are low-speed gears.
    • They are unable to transfer power between axes that are not parallel.
    • When used at high speeds, spur gears make too much noise.
    • The teeth on the wheel are under a lot of strain.
    • They are not suitable for long-distance energy transfer.
  • Gears are employed in mechanical devices to convey motion and torque between machine components. Gears can change the direction of movement and/or increase the output speed or torque depending on the design and construction of the gear pair used.

  • Non-digital clocks, automobiles, drills, manual can openers, and bicycles are examples of everyday objects using gears. Gears can also be used to "extend the physical limits of the human body." Gears are available on powered wheelchairs and elevators.

  • Gear ratios can be summarised as follows: higher ratios (with a lower numerical value) provide stronger torque and acceleration, while lower ratios provide higher top speeds and better fuel economy. To reach a given speed, higher ratios require the engine to run quicker.


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tags :ESE & GATE MEGeneralGATE ME OverviewGATE ME Exam AnalysisGATE ME Question PapersGATE ME Answer KeyGATE ME Cutoff

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