A doorknob is a type of simple machine, specifically a wheel and axle. The knob represents the wheel, while the central shaft or rod of the doorknob represents the axle. The wheel and axle machine consists of a round wheel that works together with an axle so that the two rotate together. This simple machine works in the same way as a first-class lever, with the fulcrum being the axle to which the wheel applies a force. When the knob on one side of the door is turned, the shaft retracts the spring-loaded latch that holds the door closed. Without the knob in place, more force would be needed to turn the shaft and retract the latch.