A doorknob is referred to as a wheel and axle because both the knob and the rod within the door rotate around the same axis. A wheel and axle can also be seen as a kind of lever in situations like a doorknob.
A wheel and axle are frequently thought of as a device to lessen surface friction so that an object can be moved easily from one location to another. The wheel-and-axle system used in automobiles and bicycles is of this type.
When a force is applied to the object in this configuration, it is easier to move because of the wheel’s smaller surface area in comparison to the axle and its larger size. An object can usually be rolled more easily with a larger wheel.
A form of lever can be created using the wheel and axle. Greater torque is produced on the axle when a force is applied to the outer rim of a wheel than when the same force is applied to an axle without a wheel.
This is so that a mechanical advantage can be created by using the wheel as a lever. The mechanical advantage increases with wheel size and makes turning the axle easier. A doorknob produces a wheel-and-axle system of this kind.