A wheel is a rotating component (typically circular in shape) intended to turn on an axle bearing. The wheel is one of the key 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 transportation, supporting loads, and performing work in machines. Wheels are also used for other purposes, such as a ship's wheel, steering wheel, potter's wheel, and flywheel.
Common examples can be found in transport applications. A wheel reduces friction by facilitating motion by rolling together with the use of axles. For a wheel to rotate, a moment must be applied to the wheel about its axis, either by gravity or by the application of another external force or torque.
Terminology The English word wheel comes from the Old English word , from Proto-Germanic , from Proto-Indo-European , an extended form of the root . Cognates within Indo-European include Icelandic , Greek , and Sanskrit , the last two both meaning or .
History
The wheel undoubtedly evolved from pre-historic use of rollers (round tree logs) to move heavier objects such as rock slabs and bigger logs. The invention of the solid wooden wheel (disk on axle) dates to 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 pre-pottery Neolithic.
4500–3300 BCE (Copper Age): invention of the potter's wheel; earliest solid wooden wheels (disks with a hole for the axle); earliest wheeled vehicles 3300–2200 BCE (Early Bronze Age) 2200–1550 BCE (Middle Bronze Age): invention of the spoked wheel and the chariot; domestication of the horse
The Halaf culture of 6500–5100 BCE is sometimes credited with the earliest depiction of a wheeled vehicle, but there is no evidence that Halafians used wheeled vehicles or pottery wheels. Potter's wheels are thought to have been used in the 4th millennium BCE in the Middle East. The oldest surviving example of a potter's wheel was thought to be one found in Ur (modern Iraq) dating to approximately 3100 BCE. However, a potter's wheel found in western Ukraine, of the Cucuteni–Trypillia culture, dates to the middle of the 5th millennium BCE which predates the earliest use of the potter's wheel in Mesopotamia.Holm, Hans J. J. G.: The Earliest Wheel Finds, their Archaeology and Indo-European Terminology in Time and Space, and Early Migrations around the Caucasus. Series Minor 43. ARCHAEOLINGUA ALAPÍTVÁNY, Budapest, 2019. . Wheels of uncertain dates have been found in the Indus Valley civilization of the late 4th millennium BCE covering areas of modern India and Pakistan.
The oldest indirect evidence of wheeled movement was found in the form of miniature clay wheels north of the Black Sea before 4000BCE. From the middle of the 4th millennium BCE onward, the evidence is condensed throughout Europe in the form of toy cars, depictions, or ruts, with the oldest find in Northern Germany dating back to around 3400BCE.Holm, Hans J. J. G. "The Earliest Wheel Finds, Their Archeology and Indo-European Terminology in Time and Space, and Early Migrations around the Caucasus". Archaeolingua Alapítvány, Budapest, 2019, 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.3500–3350BCE. In the second half of the 4thmillennium BCE, evidence of wheeled vehicles appeared near-simultaneously in the Northern (Maykop culture) and South Caucasus and Eastern Europe (Cucuteni–Trypillia culture).
Depictions of a wheeled vehicle appeared between 3631 and 3380 BCE in the Bronocice clay pot excavated in a Funnelbeaker culture settlement in southern Poland. In nearby Olszanica, a 2.2m wide door was constructed for wagon entry; this barn was 40m long with three doors, dated to 5000 BCE, and belonged to the Neolithic Linear Pottery culture. Surviving evidence of a wheel-axle combination, from Stare Gmajne near Ljubljana in Slovenia (wooden Ljubljana Marshes Wheel), is dated within two standard deviations to 3340–3030 BCE, the axle to 3360–3045 BCE.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. 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.Fowler, Chris; Harding, Jan and Hofmann, Daniela (eds.) (2015). The Oxford Handbook of Neolithic Europe. OUP Oxford. . p. 109. Some historians believe that there was a diffusion of the wheeled vehicle from the Near East to Europe around the mid-4th millennium BCE.
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 from 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 1stmillennium BCE.
In China, wheel tracks dating to around 2200BCE have been found at Pingliangtai, a site of the Longshan Culture. 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 and 1500BCE.Barbieri-Low, Anthony (February 2000) "Wheeled Vehicles in the Chinese Bronze Age (c. 2000–741 B.C.E)", pp. 11-12. Sino-Platonic Papers Wheeled vehicles were introduced to China from the west.
In Britain, a large wooden wheel, measuring about in diameter, was uncovered at the Must Farm site in East Anglia in 2016. The specimen, dating from 1,100 to 800 BCE, represents the earliest and most complete 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 a wetland, indicating that the settlement had some link to dry land.
Although large-scale use of wheels did not occur in the Americas before European contact, numerous small wheeled artifacts, identified as children's toys, have been found in Mexican archeological sites, some dating to approximately 1500 BCE. Some argue that the primary obstacle to large-scale development of the wheel in the Americas was the absence of domesticated large animals that could be used to pull wheeled carriages. The closest relative of cattle 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. The only large animal that was domesticated in the Western hemisphere, the llama, a pack animal, was not physically suited to use as a draft animal to pull wheeled vehicles, and use of the llama did not spread far beyond the Andes by the time of the arrival of Europeans.
On the other hand, Mesoamericans never developed the wheelbarrow, the potter's wheel, nor any other practical object with a wheel or wheels. Although part of several toys, very similar to those found throughout the world and still made for children ("pull toys"), the wheel was never put into practical use in Mesoamerica before the 16th century. Possibly the closest the Mayas came to the utilitarian wheel is the spindle whorl, and some scholars believe that these toys were originally made with spindle whorls and spindle sticks as "wheels" and "axes".
Aboriginal Australians traditionally used circular discs rolled along the ground for target practice.
Nubians from after about 400BCE used wheels for spinning pottery and as water wheels. It is thought that Nubian waterwheels may have been ox-driven. It is also known that Nubians used horse-drawn chariots imported from Egypt.
Starting from the 18th century in West Africa, wheeled vehicles were mostly used for ceremonial purposes in places like Dahomey. The wheel was barely used for transportation, except Ethiopia and Somalia in Sub-Saharan Africa well into the 19th century.
The spoked wheel was in continued use without major modification until the 1870s, when wire-spoked wheels and pneumatic tires were invented.bookrags.com – Wheel and axle Pneumatic tires can greatly reduce rolling resistance and improve comfort. Wire spokes are under tension, not compression, which makes the wheel 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 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
A wheeled vehicle requires much less work to move than simply dragging the same weight. The low resistance to motion is explained by the fact that the frictional work done is no longer at the surface that the vehicle is traversing, but in the bearings. In the simplest and oldest case, the bearing is just a round hole through which the axle passes (a "plain bearing"). Even with a plain bearing, the frictional work is greatly reduced because: The normal force at the sliding interface is the same as with simple dragging. The sliding distance is reduced for a given distance of travel. The coefficient of friction at the interface is usually lower.
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 surfaces only slide over each other by 0.5 m. The work done is 981 × 0.25 × 0.5 = 123 joules; this is 1/40 of the work done in dragging.
Additional energy is lost from the wheel-to-road interface. This is termed rolling resistance, which is predominantly a loss due to deformation. It depends on the nature of the ground, the wheel material, the tire inflation level, the net torque exerted by the engine, and many other factors.
A wheel can also offer advantages when traversing irregular surfaces if its radius is sufficiently large relative to the irregularities.