Wheel

From Free net encyclopedia

For other uses, see Wheel (disambiguation).

Image:Steam locomotive driving wheel.jpg A wheel is a circular object that, together with an axle, allows low friction in motion by rolling. Common examples are found in transport applications. More generally the term is also used for other circular objects that rotate or turn, such as a Ship's wheel and flywheel.

1 History of the wheel and axle
2 Mechanics and function
3 References
4 Wheeled vehicles
5 Alternative options to wheels
6 See also
7 External links

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History of the wheel and axle

Image:Standard of Ur chariots.jpg Notably, there are no wheels in animals or plants though some animals can roll.

The wheel is regarded as one of the oldest and most important inventions which, according to most authorities, originated in ancient Mesopotamia during the 5th millennium BC, originally in the function of potter's wheels. When one speaks of the invention of the wheel, however, one is mainly speaking of the invention of wheeled vehicles.

The earliest undisputed depiction of a wheeled vehicle in the entire world (here a wagon -- four wheels, two axles), is on the Bronocice pot, a ca. 4000 BC clay pot excavated in southern Poland.

The wheel reaches Europe in the 4th millennium, and India with the Indus Valley Civilization in the 3rd millennium. In China, the wheel is certainly present with the adoption of the chariot in ca. 1200 BC, and Barbieri-Low (2000) argues for earlier Chinese wheeled vehicles, circa 2000 BC.

Although they did not develop the wheel proper, the Olmec 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, Australia, and the Americas until relatively recent contacts with Eurasians.

Image:Wheel Iran.jpg

The invention of the wheel thus falls in the late Neolithic and may be seen in conjunction with the other technological advances that gave rise to the early Bronze Age. Note that this implies the passage of several wheel-less millennia, even after the invention of agriculture.

Early wheels were simple wooden disks with a hole for the axle. Note that because of the structure of wood a horizontal slice of a trunk is not suitable, rounded pieces of longitudinal boards are required. The oldest such wheel was found by the Slovenian archeologist dr. Anton Velušček and his team in 2002 at the Ljubljana Marshes (Ljubljansko barje), some 20 kilometres southeast of Ljubljana, Slovenia.[1] According to the experts in Vienna, Austria, the specimen was manufactured somewhere between 3350 and 3100 BC and is even older than others of such kind found in Switzerland and Germany.

In the early Roman empire, most horse-carts used a design featuring two chords across the wheel.Template:Ref The spoked wheel was invented much more recently, and allowed the construction of lighter and swifter vehicles. The earliest known examples are in the context of the Andronovo culture, dating to ca 2000 BC (see chariot). Celtic chariots introduced an iron rim around the wheel in the 1st millennium BC. The spoked wheel was in continued use without major modification until the early 20th century.

The invention of the wheel turned out to be of great importance not only as a transportation device, but for the development of technology in general, important applications including the water wheel, the cogwheel (see also antikythera mechanism), the spinning wheel, the astrolabe or torquetum. More modern descendants of the wheel include the propeller, the jet engine, the flywheel (gyroscope) and the turbine.

The central importance of the wheel also resulted in its becoming a strong cultural and spiritual metaphor for a cycle or regular repetition (see chakra, reincarnation). In the coat of arms of Panama a winged wheel is a symbol of progress.

In July 2001, the wheel was the object of an innovative, but non-inventive, patent as a "circular transportation facilitation device".Template:Ref The patent was obtained by John Keogh, a lawyer from Melbourne, Australia, with the declared intention of demonstrating the unfairness and inaccuracy of the recent innovations in the Australian patent system.

Image:Aprilia disc brake.jpg

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Mechanics and function

Wheels are used in conjunction with an axle, either the wheel turns on the axle or the axle turns in the vehicle body. The mechanics are the same in either case.

The low resistance to motion (compared to dragging) is explained as follows (refer to friction):

the normal force at the sliding interface is the same.
the sliding distance is reduced for a given distance of travel.
the coefficient of friction at the interface is usually lower.

Bearings are used to reduce friction at the interface.

Example:

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 (work=force x distance) 981 × 0.5 × 10 = 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, and say the wheel diameter is 1000 mm and axle diameter is 50 mm. So while the object still moves 10 m the sliding frictional surfaces only slide over each other a distance of 0.5 m. The work done is 981 x 0.1 x 0.5 = 49 joules.