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

AxisWhere the shaft passes through
CogA tooth on a wheel
CylinderThe "wheel" portion of the gear
Driver GearA gear rotated by a power source
Driven GearA gear rotated by a driver gear
Gear ratioThe ratio of the sizes of two gears, typically the driver gear over the driven gear
Gear trainThe combination of two or more gears
Pitch CircleThe circumference the the gear, measured at the point of force between two meshed gears
ToothThe lever protruding from the cylinder or cone

Video Introduction to Gears

Resources for Learning About Gears

Broader Topics Related to Gears

Angular Motion

The basics of angular motion

Mechanical Advantage

Learn about mechanical advantage

Mechanical Engineering

Build and deconstruct mechanical devices


Learn about torque: Force that causes an object to rotate around an axis.

Gears Knowledge Graph