A wheel is a circular part that turns on an axis, usually on or together with an axle. When a load rolls on wheels instead of being dragged, the sliding friction of the load against the ground is replaced by much smaller rolling resistance plus friction at the axle. That makes it far easier to move heavy loads. Wheels are also used in machines to transmit and convert motion, in devices such as the potter's wheel, the water wheel, gears, pulleys and turbines. The wheel probably appeared in the 4th millennium BCE. It is usually counted among the most important technologies in human history.
Origins
Wooden wheels rot easily, so the date and place of the first wheel cannot be known exactly. Archaeologists rely on surviving wheels, models and pictures. The potter's wheel is often thought to be older than the vehicle wheel. Some scholars suggest that early Mesopotamian potters used a turntable in the 4th millennium BCE, before the wheel was put to use in transport.
One of the best-dated early pictures of a wheeled vehicle is on the Bronocice pot. Depictions of a wheeled vehicle appeared between 3500 and 3350 BCE in the Bronocice clay pot excavated in a Funnelbeaker culture settlement in southern Poland. The picture suggests the existence of wagons in Central Europe as early as in the late 4th millennium BCE. They were presumably drawn by aurochs whose remains were found with the pot. Wheeled vehicles appear at about the same time in Mesopotamia, the North Caucasus and the Pontic–Caspian steppe. Because the evidence is spread so widely, scholars still disagree about whether the wheel was invented once and spread, or invented in several places.
The oldest wheel yet found is the Ljubljana Marshes Wheel. It was discovered by achaeologists on 29 March 2002 near Ljubljana, Slovenia. Having a diameter of 70 centimetres, the wheel is made of ash and oak. The aperture for the 120-centimetre-long axle is square, which means that the wheel and the axle rotated together. Radiocarbon dates place the wheel within two standard deviations to 3340–3030 BCE, the axle to 3360–3045 BCE.
Solid and spoked wheels
The earliest vehicle wheels were solid discs. Most were made from two or three wooden planks held together with crossbars, not cut as a slice from a tree trunk. Solid wheels were strong, but they were heavy and slow, so they suited ox-drawn carts and wagons.
The spoked wheel was a major advance. The earliest physical evidence for spoked wheels was found in the Sintashta culture, dating to c. 2000 BCE. These Bronze Age burials in the southern Urals contain wheel imprints that show spokes. The spoked wheel made it possible to build light, fast, horse-drawn vehicles, and the chariot soon became an important military technology across Eurasia. Scholars disagree about whether the Sintashta vehicles were true chariots. Some disagree that the Sintashta culture vehicle finds are true chariots, but rather classed as carts. Chariots appear in Ancient Egypt, Anatolia, Ancient Greece and Shang-dynasty China in the 2nd millennium BCE.
Later improvements included iron tyres, hubs with separate bearings, and wheels built from shaped felloes (rim segments). Celtic chariots (800–450 BC) are the first known examples to use an iron rim around the wheel. In the Roman Empire, paved roads and standard vehicle designs supported large-scale overland trade. In China, the wheelbarrow is recorded by the Han dynasty. It let one person move heavy loads along narrow paths.
Regions without wheeled transport
The wheel did not spread everywhere. In Mesoamerica, people knew the principle of the wheel but did not use it to carry loads. Archeologists have discovered approximately 100 wheeled figurines across Veracruz, Michoacan, Guerrero, and El Salvador. These toys typically depict animals—mostly dogs and jaguars—with axles threaded through leg loops and wheels on each end. Common explanations include the lack of large draft animals, rugged terrain, and the absence of roads suited to wheeled vehicles. Wheeled transport also fell out of use in parts of the Middle East and North Africa from late antiquity. Camel caravans proved cheaper there than carts.
Mechanics
In classical mechanics, the wheel and axle is one of the classical simple machines. A force applied at the rim of a large wheel produces a larger turning force (torque) at a small axle, and the reverse is also true. The mechanical advantage equals the ratio of the two radii. Windlasses, capstans, steering wheels and screwdrivers all rely on this principle.
A rolling wheel has two main kinds of resistance:
- Rolling resistance, which comes from the wheel and the surface deforming under the load.
- Bearing friction, at the axle.
Lubrication greatly reduces bearing friction, and so does the rolling-element bearing, developed in its modern form in the 18th and 19th centuries. A rotating wheel also stores kinetic energy. The amount depends on how its mass is distributed around the axis (its moment of inertia). Flywheels use this property to smooth out uneven power delivery.
Wheels in power and industry
Wheels were also used to drive machines. The water wheel was described in the Hellenistic world by about the 3rd century BCE and later spread across Eurasia. For centuries it powered mills that ground grain, worked bellows and drove trip hammers. Gear wheels transmitted power and controlled the speed and direction of rotation in machines ranging from the Antikythera mechanism to mechanical clocks.
During the Industrial Revolution, flywheels, pulleys and gear trains linked steam engines to factory machinery. Railways ran flanged iron wheels on iron rails, which cut rolling resistance even further. Turbines, the modern descendants of the water wheel, now drive most electric generators. Electric motors turn the wheels of trains and of many road vehicles.
Modern wheels and tyres
In the 19th century, wheels became lighter and gave a smoother ride. Wire-spoked wheels under tension appeared on the bicycle in the 1870s. The pneumatic tyre was patented by Robert William Thomson in 1847. The first mass-produced tire was made in 1888 on May Street, Belfast, by another Scot: John Boyd Dunlop. Pneumatic tyres absorb shocks and grip the road better, and they became standard on bicycles and then on the automobile.
Today, road vehicles use wheels of pressed steel or alloy fitted with tubeless radial tyres. Railway wheels are still solid steel. Aircraft landing gear, planetary rovers and many robots also run on specially designed wheels. Beyond transport and machinery, the wheel has long served as a symbol. Examples include the Buddhist dharma wheel, the medieval wheel of fortune, and wheel emblems on flags and coats of arms.
References
- Wheel and axleen.wikipedia.org
- Bronocice poten.wikipedia.org
- Oldest wheelguinnessworldrecords.com
- Ljubljana Marshes Wheelen.wikipedia.org
- Spokeen.wikipedia.org
- Charioten.wikipedia.org
- Who Invented the Wheel - A Brief History - Bricsys Blogbricscad.octave.com
- When Was the Wheel Invented? New Archeological Evidence Changes Everythingperformanceplustire.com