Wheel

Wheel, circular frame or disc, constructed to revolve on a central axis, and constituting an integral feature of most ground vehicles and conveyances. The earliest known wheels, constructed in ancient Mesopotamia, date from about 3500 to 3000 bc (see Technology). Wheeled vehicles are believed to have appeared after the invention of the potter's wheel, and the wheeled cart soon replaced the sledge as a means of transport. In its simplest form, the wheel was a solid wooden disc mounted on a round axle, to which it was secured by wooden pins. Eventually sections were carved out of the disc to reduce the weight, and radial spokes were devised about 2000 bc.

The invention of the wheel was a major turning point in the advance of human civilization. The wheel led to more efficient use of animal power for agriculture and other work and it became an invaluable mechanical means for controlling the flow and direction of power or force. The applications of the wheel in modern life and technology are virtually infinite. See Gear; Pulley.