A gear is a special type of lever, and is therefore considered a simple machine. The reason a gear is like a lever is due to the teeth in the gear. Each tooth exerts pressure on another, causing the gear to move.
Gears are a first-class lever, as a part of the wheel and axle category. All levers have a rigid arm and a fulcrum, which is a fixed point on which the arm pivots. For wheels and gears, the axle acts as the fulcrum, while the arms are the spokes or teeth of the wheel or gear. Other examples of first-class levers include a car jack, a pair of scissors or a water pump.