A gear is a component within a transmission device that transmits rotational force to another gear or device.
How do gears work
In the simplest terms a gear is a way to generate speed or power or change the direction of power. Most gears are mounted on shafts, generally an input and output shaft. When two gears are meshing (connected) they are called a transmission.
Gears can be used to do the following things
Increase or Decrease Speed
By connecting two gears together, Gear A with 20 teeth and Gear B with 10 teeth. Gear B will have to turn around much faster to keep up with gear A, however it does so with half as much turning force.
To increase the force of gears, the second gear in a pair of gears will have fewer teeth than our first gear, it will turn slower but will do so with more force.
When two gears are meshing together, the second gear always turns in the opposite direction to the first gear. So if Gear A is turning clockwise, Gear B will turn anti-clockwise. If you had three gears meshing together A and B would be turning clockwise, whilst B would be turning anti-clockwise.