One of the most important innovations in human material culture, allowing continuous rotary motion, and the continuous conversion of rotary motion into linear motion, and vice versa. The earliest wheels are found c.3500 BC; the earliest with spokes c.2000 BC. The first were sections of tree trunks, but later types were built up of planks joined and cut to shape. Other improvements were the separate axle, the reinforced hub, which could be lubricated, and the metal tyre, which strengthened the rim.
More generally the term is also used for other circular objects that rotate or turn, such as a Ship's wheel and flywheel.History of the wheel and axle
The English word "wheel" comes from the Proto-Indo-European *kwekwlo-, which meant "circle" and which was an extended form of the root *kwel- meaning "to revolve, move around, sojourn, dwell".
Notably there are no macroscopic wheels in macroscopic animals or plants, though some animals can roll.
Most authorities regard the wheel as one of the oldest and most important inventions, which originated in ancient Sumer in Mesopotamia (modern Iraq) in the 5th millennium BC, originally in the function of potter's wheels. The wheel reached India and Pakistan with the Indus Valley Civilization in the 3rd millennium BC. 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 in, from maybe 2000 BC. The earliest depiction of what may be a wheeled vehicle (here a wagon -- four wheels, two axles), is on the Bronocice pot, a ca.
The wheel reached Europe and India (the Indus Valley civilization) in the 4th millennium BC. 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. Whether there was an independent "invention of the wheel" in East Asia or whether the concept made its way there after jumping the Himalayan barrier remains an open question.
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 children's toys dating to about 1500 BC.
The invention of the wheel thus falls in the late 1800s and may be seen in conjunction with the other technological advances that gave rise to the early 2000s. That people with capacities fully equal to our own walked the earth for so long before conceiving of the wheel may be initially surprising, but populations were extremely small through most of this period and the wheel, which requires an axle and socket to be actually useful, is not so simple a device as it may seem.
Early wheels too were simple wooden disks with a hole for the axle.
The spoked wheel was invented more recently, and allowed the construction of lighter and swifter vehicles. Celtic chariots introduced an iron rim around the wheel in the 1st millennium BC. The spoked wheel has been in continued use without major modification until the 1870s, when wire wheels and pneumatic tyres were invented .
The invention of the wheel has also been important for technology in general, important applications including the water wheel, the cogwheel (see also antikythera mechanism), the spinning wheel, and the astrolabe or torquetum.
The wheel has also become a strong cultural and spiritual metaphor for a cycle or regular repetition (see chakra, reincarnation, Yin and Yang among others).
In July 2001, the wheel was the object of an Australian "innovation patent" as a "circular transportation facilitation device". Applications for innovation patents, like Mr. Keogh's wheel application, are not examined by IP Australia, the Australian Patent Office, before they are registered.
Mechanics and function
The wheel (with axle) is considered one of the simple machines and lies near the starting point of advanced human technology (advanced, that is, in comparison with even earlier mechanical innovations such as stone/bone knives and axes, tension-sprung projectiles, scoops and shovels).
When wheels are used in conjunction with axles, either the wheel turns on the axle or the axle turns in a vehicle (as in a cart) or a housing (as in a mill). 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.
Additional energy is lost at the wheel to road interface.
Wheeled vehicles
Vehicles can be classified according to number of wheels:
Unicycle, monocycle Bicycle Tricycle QuadricycleAlternatives to wheels
While wheels are used for ground transport very widely, there are alternatives, some of which are suitable for terrain where wheels are ineffective. Alternative methods for ground transport without wheels include
Dragging with runners (sled) or without (travois) Being carried (litter/sedan chair or stretcher) Being raised by air pressure (hovercraft) Being raised by electromagnetic energy (maglev train) Riding an animal such as a horse Walking on ones own legs A walking machine
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