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In its primitive form, a wheel is a circular block of a hard and durable material at whose center has been bored a circular hole through which is placed an axle bearing about which the wheel rotates when a moment is applied by gravity or torque to the wheel about its axis, thereby making together one of the six simple machines. When placed vertically under a load-bearing platform or case, the wheel turning on the horizontal axle makes it possible to transport heavy loads; when placed horizontally, the wheel turning on its vertical axle makes it possible to control the spinning motion used to shape materials (e.g. a potter's wheel); when mounted on a column connected to a rudder or a chassis mounted on other wheels, one can control the direction of a vessel or vehicle (e.g. a ship's wheel or steering wheel); when connected to a crank or engine, a wheel can store, release, or transmit energy (e.g. the flywheel).

Etymology

The English word wheel comes from the Old English word hweol, hweogol, from Proto-Germanic *hwehwlan, *hwegwlan, from Proto-Indo-European *kwekwlo-,[1] an extended form of the root *kwel- "to revolve, move around". Cognates within Indo-European include Icelandic hjól "wheel, tyre", Greek κύκλος kúklos, and Sanskrit chakra, the latter two both meaning "circle" or "wheel".[2]

History

The invention of the solid wooden disk wheel falls into the late Neolithic, and may be seen in conjunction with other technological advances that gave rise to the early Bronze Age. This implies the passage of several wheel-less millennia even after the invention of agriculture and of pottery, during the Aceramic Neolithic.

A depiction of an onager-drawn cart on the Sumerian "battle standard of Ur" (c. 2500 BCE)

The Halaf culture of 6500–5100 BCE is sometimes credited with the earliest depiction of a wheeled vehicle, but this is doubtful as there is no evidence of Halafians using either wheeled vehicles or even pottery wheels.[3] Precursors of wheels, known as "tournettes" or "slow wheels", were known in the Middle East by the 5th millennium BCE. One of the earliest examples was discovered at Tepe Pardis, Iran, and dated to 5200–4700 BCE. These were made of stone or clay and secured to the ground with a peg in the center, but required significant effort to turn. True potter's wheels, which are freely-spinning and have a wheel and axle mechanism, were developed in Mesopotamia (Iraq) by 4200–4000 BCE.[4] The oldest surviving example, which was found in Ur (modern day Iraq), dates to approximately 3100 BCE.[5]

The oldest indirect evidence of wheeled movement was found in the form of miniature clay wheels north of the Black Sea before 4000 B.C. From the middle of the 4th millennium BCE onwards, the evidence is condensed throughout Europe in the form of toy cars, depictions, or ruts.[6] In Mesopotamia, depictions of wheeled wagons found on clay tablet pictographs at the Eanna district of Uruk, in the Sumerian civilization are dated to c. 3500–3350 BCE.[7] In the second half of the 4th millennium BCE, evidence of wheeled vehicles appeared near-simultaneously in the Northern (Maykop culture) and South Caucasus (Early Kurgan culture) and Eastern Europe (Cucuteni-Trypillian culture). Depictions of a wheeled vehicle appeared between 3500–3350 BCE in the Bronocice clay pot excavated in a Funnelbeaker culture settlement in southern Poland.[8] In nearby Olszanica, a 2.2 m wide door was constructed for wagon entry; this barn was 40 m long with 3 doors.[9] Surviving evidence of a wheel-axle combination, from Stare Gmajne near Ljubljana in Slovenia (Ljubljana Marshes Wooden Wheel), is dated within two standard deviations to 3340–3030 BCE, the axle to 3360–3045 BCE.[10] Two types of early Neolithic European wheel and axle are known; a circumalpine type of wagon construction (the wheel and axle rotate together, as in Ljubljana Marshes Wheel), and that of the Baden culture in Hungary (axle does not rotate). They both are dated to c. 3200–3000 BCE.[11] Some historians believe that there was a diffusion of the wheeled vehicle from the Near East to Europe around the mid-4th millennium BCE.[12]

Solid wheels on a heavy temple car, contrasted with the lighter wire-spoked wheels of the black roadster bicycle in the foreground

Early wheels were simple wooden disks with a hole for the axle. Some of the earliest wheels were made from horizontal slices of tree trunks. Because of the uneven structure of wood, a wheel made from a horizontal slice of a tree trunk will tend to be inferior to one made from rounded pieces of longitudinal boards.

The spoked wheel was invented more recently, and allowed the construction of lighter and swifter vehicles. The earliest known examples of wooden spoked wheels are in the context of the Sintashta culture, dating to c. 2000 BCE (Krivoye Lake). Soon after this, horse cultures of the Caucasus region used horse-drawn spoked-wheel war chariots for the greater part of three centuries. They moved deep into the Greek peninsula where they joined with the existing Mediterranean peoples to give rise, eventually, to classical Greece after the breaking of Minoan dominance and consolidations led by pre-classical Sparta and Athens. Celtic chariots introduced an iron rim around the wheel in the 1st millennium BCE.

Qatar Airways Airbus A380 arrives at London Heathrow Airport. It has twenty main undercarriage wheels (four + four on the wing, and six + six on the fuselage). (2015)

In China, wheel tracks dating to around 2200 BCE have been found at Pingliangtai, a site of the Longshan Culture.[13] Similar tracks were also found at Yanshi, a city of the Erlitou culture, dating to around 1700 BCE. The earliest evidence of spoked wheels in China comes from Qinghai, in the form of two wheel hubs from a site dated between 2000-1500 BCE.[14]

In Britain, a large wooden wheel, measuring about 1 m (3.3 ft) in diameter, was uncovered at the Must Farm site in East Anglia in 2016. The specimen, dating from 1,100–800 BCE, represents the most complete and earliest of its type found in Britain. The wheel's hub is also present. A horse's spine found nearby suggests the wheel may have been part of a horse-drawn cart. The wheel was found in a settlement built on stilts over wetland, indicating that the settlement had some sort of link to dry land.[15]

A figurine featuring the New World's independently invented wheel

Although large-scale use of wheels did not occur in the Americas prior to European contact, numerous small wheeled artifacts, identified as children's toys, have been found in Mexican archeological sites, some dating to about 1500 BCE.[16] It is thought that the primary obstacle to large-scale development of the wheel in the Americas was the absence of domesticated large animals which could be used to pull wheeled carriages.[17] The closest relative of cattle present in Americas in pre-Columbian times, the American Bison, is difficult to domesticate and was never domesticated by Native Americans; several horse species existed until about 12,000 years ago, but ultimately became extinct.[18] The only large animal that was domesticated in the Western hemisphere, the llama, a pack animal but not physically suited to use as a draft animal to pull wheeled vehicles,[19] did not spread far beyond the Andes by the time of the arrival of Columbus.

Nubians from after about 400 BCE used wheels for spinning pottery and as water wheels.[20] It is thought that Nubian waterwheels may have been ox-driven.[21] It is also known that Nubians used horse-drawn chariots imported from Egypt.[22]

The wheel was barely used, with the exception of the Horn of Africa, in Sub-Saharan Africa well into the 19th century but this changed with the arrival of the Europeans.[23][24]

The spoked wheel was in continued use without major modification until the 1870s, when wire-spoked wheels and pneumatic tires were invented.[25] The wire spokes are under tension, not compression, making it possible for the wheel to be both stiff and light. Early radially-spoked wire wheels gave rise to tangentially-spoked wire wheels, which were widely used on cars into the late 20th century. Cast alloy wheels are now more commonly used; forged alloy wheels are used when weight is critical.

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. More modern descendants of the wheel include the propeller, the jet engine, the flywheel (gyroscope) and the turbine.

Mechanics and function

Main article: wheel and axle

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 help reduce friction at the interface. In the simplest and oldest case the bearing is just a round hole through which the axle passes (a "plain bearing").

Example:

  • If a 100 kg object is dragged for 10 m along a surface with the coefficient of friction 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, for wood, μ = 0.25, 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 × 0.25 × 0.5 = 123 joules; the work done has reduced to 1/40 of that of dragging.

Additional energy is lost from the wheel-to-road interface. This is termed rolling resistance which is predominantly a deformation loss. This energy is also lowered by the use of a wheel (in comparison to dragging) because the net force on the contact point between the road and the wheel is almost perpendicular to the ground, and hence, generates an almost zero net work. This depends on the nature of the ground, of the material of the wheel, its inflation in the case of a tire, the net torque exerted by the eventual engine, and many other factors.

A wheel can also offer advantages in traversing irregular surfaces if the wheel radius is sufficiently large compared to the irregularities.

The wheel alone is not a machine, but when attached to an axle in conjunction with bearing, it forms the wheel and axle, one of the simple machines. A driven wheel is an example of a wheel and axle. Wheels pre-date driven wheels by about 6000 years, themselves an evolution of using round logs as rollers to move a heavy load—a practice going back in pre-history so far that it has not been dated.

Construction

This article is about structure of wheel. For making of wire-spoked wheels, see Wheelbuilding. For making of non-wire spoked wheels, see Wheel construction.

Rim

Main article: Rim (wheel)
An aluminium alloy wheel

The rim is the "outer edge of a wheel, holding the tire."[26] It makes up the outer circular design of the wheel on which the inside edge of the tire is mounted on vehicles such as automobiles. For example, on a bicycle wheel the rim is a large hoop attached to the outer ends of the spokes of the wheel that holds the tire and tube.

In the 1st millennium BCE an iron rim was introduced around the wooden wheels of chariots.

Hub

The hub is the center of the wheel, and typically houses a bearing, and is where the spokes meet.

A hubless wheel (also known as a rim-rider or centerless wheel) is a type of wheel with no center hub. More specifically, the hub is actually almost as big as the wheel itself. The axle is hollow, following the wheel at very close tolerances.

Spokes

Main article: spoke
A spoked wheel on display at The National Museum of Iran, in Tehran. The wheel is dated to the late 2nd millennium BCE and was excavated at Choqa Zanbil.

A spoke is one of some number of rods radiating from the center of a wheel (the hub where the axle connects), connecting the hub with the round traction surface. The term originally referred to portions of a log which had been split lengthwise into four or six sections. The radial members of a wagon wheel were made by carving a spoke (from a log) into their finished shape. A spokeshave is a tool originally developed for this purpose. Eventually, the term spoke was more commonly applied to the finished product of the wheelwright's work, than to the materials used.

Wire

Main article: wire wheel

The rims of wire wheels (or "wire spoked wheels") are connected to their hubs by wire spokes. Although these wires are generally stiffer than a typical wire rope, they function mechanically the same as tensioned flexible wires, keeping the rim true while supporting applied loads.

Wire wheels are used on most bicycles and still used on many motorcycles. They were invented by aeronautical engineer George Cayley and first used in bicycles by James Starley. A process of assembling wire wheels is described as wheelbuilding.

A 1957 MGA automobile with wire wheels

Tire/Tyre

Main articles: tire, motorcycle tire, and bicycle tire
Stacked and standing car tires

A tire (in American English and Canadian English) or tyre (in some Commonwealth Nations such as UK, India, South Africa and Australia) is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground. The word itself may be derived from the word "tie," which refers to the outer steel ring part of a wooden cart wheel that ties the wood segments together (see Etymology below).

The fundamental materials of modern tires are synthetic rubber, natural rubber, fabric and wire, along with other compound chemicals. They consist of a tread and a body. The tread provides traction while the body ensures support. Before rubber was invented, the first versions of tires were simply bands of metal that fitted around wooden wheels to prevent wear and tear. Today, the vast majority of tires are pneumatic inflatable structures, comprising a doughnut-shaped body of cords and wires encased in rubber and generally filled with compressed air to form an inflatable cushion. Pneumatic tires are used on many types of vehicles, such as cars, bicycles, motorcycles, trucks, earthmovers, and aircraft.

Alternatives

While wheels are very widely used for ground transport, there are alternatives, some of which are suitable for terrain where wheels are ineffective. Alternative methods for ground transport without wheels include:

Symbolism

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). As such and because of the difficult terrain, wheeled vehicles were forbidden in old Tibet. The wheel in ancient China is seen as a symbol of health and strength and utilized by some villages as a tool to predict future health and success. The diameter of the wheel is indicator of one's future health.

The winged wheel is a symbol of progress, seen in many contexts including the coat of arms of Panama, the logo of the Ohio State Highway Patrol and the State Railway of Thailand. The wheel is also the prominent figure on the flag of India. The wheel in this case represents law (dharma). It also appears in the flag of the Romani people, hinting to their nomadic history and their Indian origins.

The introduction of spoked (chariot) wheels in the Middle Bronze Age appears to have carried somewhat of a prestige. The sun cross appears to have a significance in Bronze Age religion, replacing the earlier concept of a Solar barge with the more 'modern' and technologically advanced solar chariot. The wheel was also a solar symbol for the Ancient Egyptians.[27]

See also

References

  1. ^ "wheel". Online Etymology Dictionary.
  2. ^ "American Heritage Dictionary Entry: wheel". Houghton Mifflin Harcourt Publishing Company.
  3. ^ V. Gordon Childe (1928). New Light on the Most Ancient East. p. 110.
  4. ^ D.T. Potts (2012). A Companion to the Archaeology of the Ancient Near East. p. 285.
  5. ^ Moorey, Peter Roger Stuart (1999) [1994]. Ancient Mesopotamian Materials and Industries: The Archaeological Evidence. Winona Lake, IN: Eisenbrauns. p. 146. ISBN 978-1-57506-042-2.
  6. ^ Hans J.J.G. Holm: The Earliest Wheel Finds, Their Archeology and Indo-European Terminology in Time and Space, and Early Migrations around the Caucasus. Archaeolingua Alapítvány, Budapest, 2019, ISBN 978-615-5766-29-9
  7. ^ Attema, P. A. J.; Los-Weijns, Ma; Pers, N. D. Maring-Van der (December 2006). "Bronocice, Flintbek, Uruk, Jebel Aruda and Arslantepe: The Earliest Evidence Of Wheeled Vehicles In Europe And The Near East". Palaeohistoria. University of Groningen. 47/48: 10–28 (11).
  8. ^ Anthony, David A. (2007). The horse, the wheel, and language: how Bronze-Age riders from the Eurasian steppes shaped the modern world. Princeton, NJ: Princeton University Press. p. 67. ISBN 978-0-691-05887-0.
  9. ^ "35. Olszanica Longhouse 6: Why has it got wide doors?". 26 October 2018.
  10. ^ Velušček, A.; Čufar, K. and Zupančič, M. (2009) "Prazgodovinsko leseno kolo z osjo s kolišča Stare gmajne na Ljubljanskem barju", pp. 197–222 in A. Velušček (ed.). Koliščarska naselbina Stare gmajne in njen as. Ljubljansko barje v 2. polovici 4. tisočletja pr. Kr. Opera Instituti Archaeologici Sloveniae 16. Ljubljana.
  11. ^ Fowler, Chris; Harding, Jan and Hofmann, Daniela (eds.) (2015). The Oxford Handbook of Neolithic Europe. OUP Oxford. ISBN 0-19-166688-2. p. 109.
  12. ^ Attema, P. A. J.; Los-Weijns, Ma; Maring-Van der Pers, N. D. (December 2006). "Bronocice, Flintbek, Uruk, Jebel Aruda and Arslantepe: The Earliest Evidence of Wheeled Vehicles in Europe and the Near East". Palaeohistoria. University of Groningen. 47/48: 10-28 (19-20).
  13. ^ "Central China discovers earliest wheel ruts". Xinhua. Retrieved 20 January 2020.
  14. ^ Barbieri-Low, Anthony (February 2000) "Wheeled Vehicles in the Chinese Bronze Age (c. 2000–741 B.C.)", p. 11-12. Sino-Platonic Papers
  15. ^ "Bronze Age wheel at 'British Pompeii' Must Farm an 'unprecedented find'". BBC. Retrieved 18 February 2016.
  16. ^ Ekholm, Gordon F (April 1946). "Wheeled Toys in Mexico". American Antiquity. 11 (4): 222–28. JSTOR 275722.
  17. ^ Diamond, Jared (1999). Guns, Germs, and Steel: The Fates of Human Societies. New York: Norton. p. 237. ISBN 978-0-393-31755-8.
  18. ^ Singer, Ben (May 2005). A brief history of the horse in America. Canadian Geographic Magazine. Archived from the original on 19 August 2014.
  19. ^ The Carriage Journal Vol 23 No 4 Spring 1986
  20. ^ "Crafts – Uncovering Treasures of Ancient Nubia". NYTimes.com. 27 February 1994.
  21. ^ "What the Nubians Ate". Discover Magazine.
  22. ^ Fage, J.D.; Oliver, Roland Anthony (1975). The Cambridge History of Africa. Cambridge University Press. ISBN 978-0-521-21592-3.
  23. ^ Chaves, Isaías; Engerman, Stanley L.; Robinson, James A. (2012). Reinventing the Wheel: The Economic Benefits of Wheeled Transportation in Early Colonial British West Africa (PDF). Weatherhead Center for International Affairs. p. 1. Archived from the original (PDF) on 6 January 2014. Retrieved 5 January 2014. One of the great technological puzzles of Sub-Saharan African economic history is that wheeled transportation was barely used prior to the colonial period. Instead, head porterage was the main method of transportation.
  24. ^ Law, Robin C. (1980). "Wheeled Transportation in Pre-Colonial West Africa". Africa. 50 (3): 249–62. doi:10.2307/1159117. JSTOR 1159117.
  25. ^ bookrags.com – Wheel and axle
  26. ^ Jewel, Elizabeth (2006). The Pocket Oxford Dictionary and Thesaurus. Oxford University Press. p. 722. ISBN 978-0-19-530715-3. Retrieved 4 January 2012.
  27. ^ Hall, Adelaide S. (2005). A Glossary of Important Symbols in Their Hebrew: Pagan and Christian Forms. p. 56. ISBN 978-1-59605-593-3.

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