A wheel is a circular component that is intended to rotate on an axial bearing. The wheel is one of the main components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be moved easily facilitating movement or transportation while supporting a load, or performing labor in machines. Wheels are also used for other purposes, such as a shipâ€™s wheel, steering wheel, potterâ€™s wheel and flywheel.
Common examples are found in transport applications. A wheel greatly reduces friction by facilitating motion by rolling together with the use of axles. In order for wheels to rotate, a moment needs to be applied to the wheel about its axis, either by way of gravity, or by the application of another external force or torque.
Evidence of wheeled vehicles appears from the mid-4th millennium BC, near-simultaneously in Mesopotamia(Sumerian civilization), Indus Valley (Mohenjodaro), the Northern Caucasus (Maykop culture) and Central Europe, so that the question of which culture originally invented the wheeled vehicle remains unresolved and under debate. The worldâ€™s oldest wooden wheel, dating from 5,250 Â± 100 BP as part of Globular Amphora Culture, was discovered by Slovenian archeologists in 2002.
The earliest well-dated depiction of a wheeled vehicle is on the Bronocice pot, a c. 3500 â€“ 3350 BC clay pot excavated in a Funnelbeaker culture settlement in southern Poland.
The wheeled vehicle spread from the area of its first occurrence (Mesopotamia, Caucasus, Balkans, Central Europe) across Eurasia, reaching the Indus Valley by the 3rd millennium BC. During the 2nd millennium BC, the spoke-wheeled chariot spread at an increased pace, reaching both China and Scandinavia by 1200 BC.
In China, the wheel was certainly present with the adoption of the chariot in c. 1200 BC, although Barbieri-Low argues for earlier Chinese wheeled vehicles, c. 2000 BC.
Although they did not develop the wheel proper, the Olmec and certain other western hemisphere cultures seem to have approached it, as wheel-like worked stones have been found on objects identified as childrenâ€™s toys dating to about 1500 BC. It is thought that the primary obstacle to large-scale development of the wheel in the Western hemisphere was the absence of domesticated large animals which could be used to pull wheeled carriages. Several horse species existed until about 12,000 years ago, but ultimately went extinct.
The wheel was barely used in Sub-Saharan Africa into the 19th century, only arriving with Europeans after they explored the region and then moved to exploit it.