Wheel | Wikipedia audio article
Wheel | Wikipedia audio article

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
The English word wheel comes from the Old English word hweol, hweogol, from Proto-Germanic
*hwehwlan, *hwegwlan, from Proto-Indo-European *kwekwlo-, 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”.==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. 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; domestication of the horse 3300–2200 BCE (Early Bronze Age)
2200–1550 BCE (Middle Bronze Age): invention of the spoked wheel and the chariot
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. 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. The oldest surviving example, which was found
in Ur (modern day Iraq), dates to approximately 3100 BCE.Evidence of wheeled vehicles appeared
by the late 4th millennium BCE. Depictions of wheeled wagons found on clay
tablet pictographs at the Eanna district of Uruk, in the Sumerian civilization of Mesopotamia,
are dated between 3700–3500 BCE. 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. In nearby Olszanica, a 2.2 m wide door was
constructed for wagon entry; this barn was 40 m long with 3 doors. 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. 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. 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 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. In China, the wheel was certainly present
with the adoption of the chariot in c. 1200 BCE, although Barbieri-Low argues for earlier
Chinese wheeled vehicles, c. 2000 BCE. 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. 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. 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. 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. 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, 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. It is thought that Nubian waterwheels may
have been ox-driven. It is also known that Nubians used horse-drawn
chariots imported from Egypt.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.The spoked wheel was in continued use without major modification
until the 1870s, when wire-spoked wheels and pneumatic tires were invented. 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==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=====
Rim===The rim is the “outer edge of a wheel, holding
the tire.” 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===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====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.===Tire/Tyre===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.==See also==
Types: Alloy wheel, Artillery wheel, Bicycle wheel, Cartwheel, Caster, Dreadnaught wheel,
Driving wheel, Flywheel, Hubless wheel, Inline skate wheel, Mansell wheel, Mecanum wheel,
Motorcycle wheel, Omni wheel, Pedrail wheel, Pressed Steel wheel, Skateboard wheel, Square
wheel, Stairclimber wheel, Steering wheel (Ship’s wheel), Train wheel, Tweel, Wire wheels
Components: Axle, Tire, Rim, Snow chains, Spoke, Wagon wheel (transportation), Wheelset
(rail transport) Inspired technologies and concepts: Breaking
wheel, Color wheel, Compact disc, Ferris wheel, Reinventing the wheel, Spindle whorl, Wagon-wheel
effect, Wheel of Fortune, Wheelbarrow, Wheel and axle
Alternatives: Magnetic levitation History: The Horse, The Wheel and Language
(book), Rotating locomotion in living systems, Terrestrial locomotion in animals: Rolling
Theory: Rolling resistance, r. friction, r. drag, Simple machine, Wheel sizing

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