Evolution of wheels.

EVOLUTION OF WHEELS:

A wheel is a circular component that is intended to rotate on an axial bearing. The wheel is one of the main 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 movement or transportation while supporting a load, or performing labor in machines. Wheels are also used for other purposes, such as a ship's wheel, steering wheel, potter's wheel and flywheel.

Common examples are found in tranport applications. A wheel greatly reduces friction by facilitating motion by rolling together with the use of axels. In order for wheels to rotate, a moment needs to be applied to the wheel about its axis, either by way of gravity, or by the application of another external force or torque.

Etymology:

The English word wheel comes from the Old English word hweol, hweogol, from Proto-Germanic *hwehwlan, *hwegwlan, from Proto-Indo-European *k^wek^wlo-, an extended form of the root *k^wel-"to revolve, move around". Cognates within Indo-European include Greek κύκλος kýklos, "wheel", Sanskrit chakra, Old Church Slavonic kolo, all meaning "circle" or "wheel".

History;

Evidence of wheeled vehicles appears from the mid-4th millennium BC, near-simultaneously in Mesopotamia(Sumerian civilization), Indus Valley(Mohenjodaro), the Northern Caucasus (Maykop culture) and Central Europe, so that the question of which culture originally invented the wheeled vehicle remains unresolved and under debate. The Ljubljana Marshes Wooden Wheel, the world's oldest known wooden wheel, dating from 5,250 ± 100BP as part of Globular Amphora Culture, was discovered by Slovenian archeologists in 2002.

The earliest well-dated depiction of a wheeled vehicle (here a wagon—four wheels, two axles) is on the Bronocice pot, a c. 3500 – 3350 BC clay pot excavated in a Funnelbeaker culture settlement in southern Poland.

The wheeled vehicle spread from the area of its first occurrence (Mesopotamia, Caucasus, Balkans, Central Europe) across Eurasia, reaching the Indus Valley by the 3rd millennium BC. During the 2nd millennium BC, the spoke-wheeled chariot spread at an increased pace, reaching both China and Scandinavia by 1200 BC.

In China, the wheel was certainly present with the adoption of the chariot in c. 1200 BC, although Barbieri-Low argues for earlier Chinese wheeled vehicles, c. 2000 BC.

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. It is thought that the primary obstacle to large-scale development of the wheel in the Western hemisphere 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 went extinct. The only large animal that was domesticated in the Western hemisphere, the llama, did not spread far beyond the Andes by the time of the arrival of Columbus.

Nubians from after about 400 BC 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-driven chariots imported from Egypt.

The wheel was barely used in Sub-Saharan Africa into the 19th century, only arriving with Europeans after they explored the region and then moved to exploit it.

The invention of the wheel thus falls in the late Neolithic, and may be seen in conjunction with other technological advances that gave rise to the earlyBronze Age. Note that this implies the passage of several wheel-less millennia even after the invention of agriculture and of pottery:

• 9500–6500 BC: Aceramic Neolithic
• 6500–4500 BC: Ceramic Neolithic (Halafian), earliest wooden wheels (disks with a hole for the axle)
• c. 4500 BC: invention of the potter's wheel, beginning of the Chalcolithic (Ubaid period)
• 4500–3300 BC: Chalcolithic, earliest wheeled vehicles, domestication of the horse
• 3300–2200 BC: Early Bronze Age
• 2200–1550 BC: Middle Bronze Age, invention of the spoked wheel and the chariot

Wide usage of the wheel was probably delayed because smooth roads were needed for wheels to be effective. Carrying goods on the back would have been the preferred method of transportation over surfaces that contained many obstacles. The lack of developed roads prevented wide usage of the wheel for transportation until well into the 20th century in less developed areas.

Early wheels were simple wooden disks with a hole for the axle. Because of the structure of wood, a horizontal slice of a tree trunk is not suitable, as it does not have the structural strength to support relevant stresses without failing; rounded pieces of longitudinal boards are required.

The spoked wheel was invented more recently, and allowed the construction of lighter and swifter vehicles. In the Harappan civilization of the Indus Valley and Northwestern India, we find toy-cart wheels made of clay with lines which have been interpreted as spokes painted or in relief, and a symbol interpreted as a spoked wheel in the script of the seals,already in the second half of the 3rd millennium BC. The earliest known examples of wooden spoked wheels are in the context of the Andronovo culture, dating to c. 2000 BC. Soon after this, horse cultures of the Caucasusregion 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 was in continued use without major modification until the 1870s, when wire wheels and pneumatic tires 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. More modern descendants of the wheel include the propeller, the jet engine, the flywheel (gyroscope) and the turbine

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 winged wheel is a symbol of progress, seen in many contexts including the coat of arms of Panama and the logo of the Ohio State Highway Patrol.

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[disambiguation needed], 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

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.

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