# Gears

## Gears have been around a long time...

Gears are one of the earliest pieces of equipment developed by man, they are regarded as one of the most significant developments in technology second only to the wheel. The use of multiple gears are more common than the use of a singular gear, these are known as a gear train.

Gear speed can be summarised by the following equation

$\frac{T_B}{T_A}=\frac{\omega _A}{\omega _B}$

where:

$T$=number of teeth on a gear

ω=angular velocity

## Gear trains change speed and force

Gear trains can be used to drastically change the rate at which something rotates. As can be seen from the video above of a 90,000,000,000:1 gear box with an input of 200 rpm the final gear will rotate once every million years.

## Gear profiles are essential

The most significant development within gearing from their early designs in ancient times is the understanding of involute properties. As can be seen from the figure below in order to achieve uniform motion the involute curves for both gears have to traced out by point g simultaneously.

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