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A wheel is a circular object that together with an axle allows low friction motion, e.g. in transport applications.
Mechanics
Wheels are used in conjunction with an axle, either the wheel turns on the axle or the wheel is rigidly attached to the axle which then turns in bearings in the body of the vehicle. The mechanics are the same in either case.
The low friction (compared to dragging) is explained as follows.
- If dragging a 100 kg object for 10 m along a surface with μ = 0.5, the normal force is 981 N and the work done (required energy) is 981 x 10 x 0.5= 4905 joules.
- Now give the object 4 wheels. The normal force between the 4 wheels and axles is the same (in total) 981 N, assume μ = 0.1, finally the most important factor is the wheel diameter (1000 mm) and axle diameter (50 mm). Now while the object still moves 10 m the sliding frictional surfaces only slide over each other a distance of 0.5 m. So work done is 981 x 0.5 x 0.1= 49 joules.
(note: additional energy is wasted at the wheel to road interface, but rather than frictional loss it is now deformation loss which can be very small e.g. train wheels on the rail tracks)
Other options
Transport devices without wheels include
History of the wheel
Most authorities credit the ancient Mesopotamians (Sumerians) with the invention of the wheel at about 4000 BC, with an independent invention in China at around 2800 BC. The Inca and certain other western hemisphere cultures seem to have approached the concept, as wheel-like worked stones have been found on objects identified as children's toys dating to about 1500 BC. The wheel was apparently unknown in Sub-saharan Africa and Australia until relatively recent contacts with Eurasians.
While the 4000 BC date for the invention of the wheel may seem ancient, it is comparatively recent on the complete human timeline (most anthropologists date the emergence of fully modern human beings (Homo sapiens) to at least 100,000 BC). That people with capacities fully equal to our own walked the earth for 96,000 years before conceiving of the wheel may be initially surprising, but populations were extremely small through most of this time and the wheel, which requires free rotation around an axle, is not so simple a device as it may seem.
In July 2001, the wheel was the object of an innovative, but non-inventive, patent as a "circular transportation facilitation device" [1] (http://news.bbc.co.uk/hi/english/world/asia-pacific/newsid_1418000/1418165.stm). The patent was obtained by John Keogh, a lawyer from Melbourne, Australia, with the declared intention of demonstrating the unfairness and inaccuracy of the modern patenting system.
See also
Other Things Called Wheels
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