Wheel

The wheel is a circular component that rotates around an axis and is used to enable movement with reduced friction by rolling rather than sliding. When paired with an axle, it forms the wheel and axle simple machine, which allows a force applied at the rim to be converted into torque at the axle and, with appropriate gearing, into linear motion of a vehicle or machine.

The earliest known wheels date to about 3500 BCE in Mesopotamia, originally for potter's wheels; by the late Bronze Age they supported wagons and chariots. Development of the spoked wheel reduced weight, while metal rims and hubs increased durability. The wheel's spread reshaped transport, agriculture, and industry across cultures.

Design and materials: Modern wheels consist of a rim, hub, and often spokes, connected to a bearing that allows rotation around the axle. Tires—solid or pneumatic—provide load distribution and shock absorption, while bearings and lubrication reduce friction and wear. Materials range from wood and steel to aluminum and composites, chosen for strength, weight, and cost.