Wheel

A wheel is a circular frame of hard material that may be solid, partly solid, or spoked and that is capable of turning on an axle. The wheel and axle is a basic machine component used for amplifying force. A modest force applied at the radius of a large gear can overcome a larger force acting at the radius of a smaller gear on the same shaft. Its mechanical advantage equals the ratio of the two forces involved and also equals the ratio of the radii of the two gears, less friction losses. The actual mechanical advantage of a wheel and axle is less than its velocity ratio because of friction.

In its earliest form the wheel and axle was probably used for raising weights or water buckets from wells. Because the wheel made controlled rotary motion possible, it was of decisive importance in machine design.

Unlike most inventions, which were inspired by the natural world, the wheel does not exist in nature and is entirely a human innovation. It was also a relative latecomer: sewing needles, woven cloth, rope, basket weaving, boats and even the flute all predated it by thousands of years. The tricky part of inventing the wheel was not conceiving of a cylinder rolling on its edge but connecting a stable, stationary platform to that cylinder. The idea of wheeled transportation may have come from the use of logs as rollers, but the oldest known wheels were wooden disks of three carved planks clamped by transverse struts.

The earliest images of wheeled carts have been excavated in Poland and elsewhere in the Eurasian steppes, and this region is overtaking Mesopotamia as the wheel's most likely birthplace. Computational analysis provides new supporting evidence for the theory that the wheel was invented by Neolithic miners harvesting copper ore from the Carpathian Mountains as early as 3900 BC. The wheel evolved over a period spanning many centuries, and its development was punctuated by discrete innovations; computational structural analysis suggests a probable path along which it evolved through a sequence of three major innovations.

The potter's wheel made an early appearance in southern Mesopotamia within the Uruk cultural sphere and then developed in a widespread and discontinuous way in the Uruk network. In Mesopotamia it was first adopted during the fourth millennium BCE. The Ubaid culture, which arose in southern Mesopotamia, is characterized by distinctive painted pottery made on a slow wheel, while the Uruk culture is characterized by mass-produced pottery made on a fast wheel or in a mold.

The use of the fast wheel became general and imparted a new crispness to pottery profiles. The potter's wheel enabled the mass production of ceramics, giving the lower classes access to affordable items such as jars and bowls.

The chronological coincidence between the adoption of wheel-coiling in northern Mesopotamia around 3900 to 3800 BCE and its adoption in the Uruk world suggests that the first adoption of the potter's wheel involved technical borrowing between the two groups. Experimental trials suggest that wheel-coiled containers of north-Mesopotamian tradition were made at around 50 to 60 rpm, while Uruk wheel-coiled containers required roughly 100 rpm.

The earliest evidence of wheeled vehicles is dated to the Funnel Beaker (TRB) culture in Europe and the Late Uruk period in the Near East, and excavation results and radiocarbon determinations from Poland, Germany, Iraq, Syria and Turkey indicate that wheeled vehicles appeared contemporaneously in Europe and the Near East. More than 150 clay models of four-wheeled wagons of the Boleraz culture of the Carpathian region are the world's earliest known representations of wheeled transport. The wheel reached the Eurasian steppe around 3100 BCE, imported as an invention from the Middle East.

Early Mesopotamian vehicle wheels were made from two half-discs of solid wood nailed together and covered with leather tires. By around 3000 BCE the Sumerians were using two- and four-wheeled carts and wagons to transport people and goods.

The oldest wooden wheel with an axle, about 5,200 years old, was discovered in Slovenia in the Ljubljana Marshes. The oldest wheel discovered so far comes from Central Europe, although the concept of the wheel is believed to have originated in Mesopotamia earlier. The wheel made its first public appearance in the City Museum of Ljubljana at the exhibition titled THE WHEEL — 5,200 years, which ran from 24 May 2013 to 20 April 2014 and was subsequently showcased in several European cities.

The chariot was an open, two- or four-wheeled vehicle of antiquity, first used in royal funeral processions and later in warfare, racing and hunting; in its light, usually two-wheeled form it was drawn by one or more horses and often carried a driver together with a fighter armed with bow-and-arrow or javelins. It apparently originated in Mesopotamia in about 3000 BCE, where monuments from Ur and Tutub depict heavy vehicles with solid wheels, and by around 3200 BCE the first chariots were made for the nobility and wealthy as personal transportation, later developed by the Akkadians and Assyrians for military use. Spoked wheels appeared about 2000 BCE, when they were in use on chariots in Asia Minor, and the introduction of the horse as a draft animal in about 2000 BCE was the final step in making the chariot a military arm that gave ancient armies unprecedented mobility.

The chariot was invented in the steppe by roughly 2000 BCE, probably just east of the southern Ural mountains where the oldest chariots have been unearthed. In Eastern Europe, light vehicles with spoked wheels and harnessed horse teams are first evidenced in the early second-millennium BC Sintashta-Petrovka culture of the South-eastern Ural Mountains. The vehicles attested at Sintashta moglia, Krivoe Ozero and Kamennyj Ambar-5 were designed to transport humans rather than goods and developed into horse-drawn chariots during Eastern Europe's Middle Bronze Age. Construction of early horse-drawn chariots with spoked wheels most probably began towards the end of the third millennium BC, and Bayesian modelling of radiocarbon dates from the Kamennyj Ambar-5 kurgan cemetery indicates early European chariots date to no later than the first proto-chariots of the ancient Near East.

The first reference to charioteers comes from Syria around 1800 BCE, after which chariots advanced into civilization and quickly became the preferred elite weapon, and the chariot served as the supreme military weapon in Eurasia from roughly 1700 BCE to 500 BCE. Chariot conquerors overran the Middle East and then invaded India about 1500 BCE, extinguishing the Indus civilization. By the time of Alexander the Great the war chariot had been superseded by cavalry, while chariot racing had become popular in Greece and a main feature of the Olympic Games; in the Roman circus games chariot racing took the foremost place and chariotry became socially important. Use of the chariot declined slowly from around 500 BCE, mainly because horseback riding, developed in the steppes, gradually replaced the need for chariots.

Numerous representations of horse-drawn chariots appear in the official scenes at Amarna, with the king and queen shown driving themselves, and the Metropolitan Museum of Art's relief Horses Harnessed to a Chariot is dated to the Amarna Period, in the reign of Akhenaten, about 1353 to 1336 B.C. Wheel spokes may be made of steel wire, laced tangentially and kept under tension by threaded nipples in the rims.

Seven AMS-dated Sintashta graves in the associated Kamennyj Ambar-5 cemetery fall between 2040 and 1730 cal BC at 95.4% confidence. For the sampled burials of kurgans 2 and 4 at Kamennyj Ambar-5, the Bayesian radiocarbon model dates chariot grave 8 in kurgan 2 to the range 1950-1880 cal BC at 95.4% confidence.

The tympanum, the commonest kind of Roman cart-wheel, was nearly a foot in thickness and was made by sawing a tree trunk across or nailing boards together. Besides its wheels and axle, the plaustrum consisted of a strong pole called the temo, to the hinder part of which a table of wooden planks was fastened. Plaustra carried loads of stone, timber, manure, or skins of wine, and their liability to overturn led the emperor Hadrian to prohibit heavily loaded waggons from entering Rome.

The three power sources of the Middle Ages — animal, water and wind — were all exploited by means of wheels, and rotating machines performing repetitive operations and driven by steam engines were important elements in the Industrial Revolution. Early waterwheels used for irrigation consisted of pots tied to the rim of a wheel rotated about a horizontal axis by running water or by a treadmill, and more than 2,000 years ago the Greeks were using water wheels to grind wheat into flour. The modern hydropower turbine traces its beginnings to the mid-1700s, when the French engineer Bernard Forest de Bélidor wrote Architecture Hydraulique.

Researchers believe the wheelbarrow first appeared in classical Greece between the sixth and fourth centuries B.C., then spread to China and later to medieval Europe.

The oldest and most common design for a perpetual motion device is the overbalanced wheel, which uses shifting weights to keep rotating. A wheel that is filmed can seem to stand still or even revolve backwards, an optical illusion called the wagon wheel effect that can also occur under a strobe light.

Daniel Burnham, the architect charged with turning a boggy square mile of Chicago into a world-dazzling showpiece, told his designers to make no little plans while he labored in the shadow of the Eiffel Tower. George Washington Gale Ferris Jr., a Pittsburgh engineer whose company inspected the steel used by the fair, quickly sketched a huge revolving steel wheel. More than 100,000 parts went into Ferris's wheel, notably an axle weighing 89,320 pounds that had to be hoisted onto two towers 140 feet in the air.

The Aztecs used wheels in children's toys, such as small wheeled dogs made of pottery or occasionally obsidian, yet never considered using wheels for transport. A cart would have been next to useless in Mesoamerica because the Aztecs had no large pack animals, and human porters were more efficient at carrying packs over long distances.

• about 3500 BCE
  Wheels at Erech
  A Sumerian pictograph from Erech shows a sledge already equipped with wheels ^{1Wheel | Invention, History & Uses · Encyclopaedia Britannica ↗}.
• around 3500 B.C.
  Potter's wheels in Mesopotamia
  The earliest wheels served as potter's wheels, roughly 300 years before anyone put wheels on chariots ^{3A Salute to the Wheel · Smithsonian Magazine ↗}.