Wheel
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.
Notably, there are no
macroscopic wheels in macroscopic animals or plants, though some animals can roll. Whether this is a case of human
ingenuity topping nature's "blind ingenuity" is a continuing source of debate.
According to most authorities, the wheel-and-axle combination originated in ancient
Mesopotamia during the
5th millennium BC, probably originally in the function of
potter's wheels. The wheel's efficient use of input energy must have been quickly understood by its inventors because it was almost immediately set to work in other contexts, most importantly in transport (vehicles) and in foodstuff processing (mill wheels).
The earliest depiction of what may be a wheeled vehicle (here a wagon -- four wheels, two axles), is on the
Bronocice pot, a ca. 4000 BC clay pot excavated in southern Poland.
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 wheel was apparently unknown in
sub-Saharan Africa,
Australia, the Pacific Islands and North America until relatively recent contacts with
Eurasians.
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. Looking back even further, it is of some interest that although paleoanthropologists now date the emergence of anatomically modern humans to ca. 150,000 years ago, 143,000 of those years were "wheel-less". 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 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, as it does not have the structural strength to support weight without collapsing; 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 similar construction found in
Switzerland and
Germany.
The
spoked wheel was invented 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. Shortly later, 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 BC. The spoked wheel has been in continued use without major modification ever since.
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, the
astrolabe or
torquetum. More modern descendants of the wheel include the
propeller, the
jet engine, the
flywheel (
gyroscope) and the
turbine.
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 the
coat of arms of Panama a
winged wheel is a symbol of progress.
In July 2001, the wheel was the object of an Australian "innovation patent" as a "circular transportation facilitation device".
[http://news.bbc.co.uk/hi/english/world/asia-pacific/newsid_1418000/1418165.stm] The innovation patent was obtained by John Keogh, a lawyer from
Melbourne, Australia, with the declared intention of demonstrating flaws in the recently introduced innovation patent system. Innovation patents are intended for minor innovations that do not qualify as patentable inventions, and an innovation patent is not the same as a
patent. Applications for innovation patents, like mr. Keogh's wheel application, are not examined by IP Australia, the Australian Patent Office, before they are registered.
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).
Since a wheel is a rigid object, it will only be non-rotating when all the
torques on it are balanced. Since forces produce larger torques when they are closer to the axis, a wheel can be used to transform between large and small forces applied by friction with belts or other wheels. The
toothed gear was fundamental to the advent of industrial class complex machines. Other variations on wheels produce the
pulley and the
windlass.
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). 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.
Additional energy is lost at the wheel to road interface. This is termed
rolling resistance which is predominantly a deformation loss.
Vehicles can be classified according to number of wheels:
#
Unicycle,
monocycle#
Bicycle#
Tricycle#
QuadricycleWhile 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*
Bicycle wheel*
Breaking wheel, a form of
torture*
Caster*
Color wheel*
Driving wheel*
Hubcap*
Magnetic levitation and
wheel-less*
Reverse rotation effect*
Rolling friction*
Ship's wheel*
Square wheel*
Stagecoach-wheel effect*
Tire*
Wagon-wheel effect*
Wheel and axle*
Simple machine *
Wheel sizing*
Wire Wheels*
Wheel Of Fortune*
Wheeled Vehicles in the Chinese Bronze Age (c. 2000-741 b.c.) by Anthony Barbieri-Low, Sino-Platonic Papers, 99 (February 2000)
*
Car Wheels - explains the different types of wheels available for cars
