wheelsandaxles

The wheel and axle is a simple machine consisting of a wheel rigidly connected to a central shaft (the axle) so they rotate together around a common axis. By applying a force to the wheel, a load attached to the axle can be moved with less effort, or the direction of the force can be changed.

Mechanical advantage is approximately the ratio of the wheel radius to the axle radius. If a force is applied at the wheel’s rim, the axle experiences a larger force roughly equal to (R_wheel / R_axle) times the input, neglecting friction. In practice, the wheel and axle enables convenient movement or lifting by trading force for distance, depending on the arrangement.

Common applications include carts and carriages, doorknobs, spools, and various hand tools. A single wheel on an axle appears in a wheelbarrow, and multiple wheels on a common axle provide stability in carts and machinery. The device often uses bearings or lubrication to reduce friction, improving efficiency.

Historically, the wheel and axle is one of the oldest known simple machines and has been used across cultures for transportation and mechanical advantage. It remains a fundamental concept in physics and engineering, and is frequently combined with other simple machines in complex mechanisms.