Gears

Gears are toothed wheels that, when combined in different configurations, can change the speed, direction, and/or torque of a power source.

Gear sizes are typically expressed by number of teeth, circumference, diameter, or radius. Gears can be used to create mechanical advantage equal to the ratio of the driver gear over the driven gear; this ratio is also referred to as the gear ratio.

Gear Terminology

Part	Definition
Axis	Where the shaft passes through
Cog	A tooth on a wheel
Cylinder	The "wheel" portion of the gear
Driver Gear	A gear rotated by a power source
Driven Gear	A gear rotated by a driver gear
Gear ratio	The ratio of the sizes of two gears, typically the driver gear over the driven gear
Gear train	The combination of two or more gears
Pitch Circle	The circumference the the gear, measured at the point of force between two meshed gears
Tooth	The lever protruding from the cylinder or cone