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The World's Greatest Invention - 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 circular objects rotating for other purposes, such as a wheel and axle and a flywheel.
History of the wheel
The wheel is regarded as one of the oldest and most important inventions, which is, according to most authorities, originated in ancient Mesopotamia in the 5th millennium BC, originally in the function of potter's wheels. A possibly independent invention in China dates to around 2800 BC. It is also thought that the invention of the wheel dated back to Ancient India. Though they did not develop the wheel proper, the Olmec and certain other western hemisphere cultures seem to have approached the concept, 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, and the Americas 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. Early wheels were simple wooden disks with a hole for the axle. In the early Roman empire, most horse-carts used a design featuring two chords across the wheel. The spoked wheel was invented much 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 (see chariot). 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 early 20th century.
The wheel is probably the most important mechanical invention of all time. Nearly every machine built since the beginning of the Industrial Revolution involves a single, basic principle embodied in one of mankindís truly significant inventions. Itís hard to imagine any mechanized system that would be possible without the wheel or the idea of a symmetrical component moving in a circular motion on an axis. From tiny watch gears to automobiles, jet engines and computer disk drives, the principle is the same.
The wheel is everywhere on all our cars, trains, planes, machines, wagons, and most factory and farm equipment. What could we move without wheels? But as important as the wheel is as an invention, we don't know who exactly made the first wheel. The oldest wheel found in archeological excavations was discovered in what was Mesopotamia and is believed to be over fifty-five hundred years old.
No one knows for sure who is ultimately responsible for the invention of the wheel although theories and speculation abound. General consensus places the invention of the wheel as we think of it at around 3500 BC, in Mesopotamia, what is modern day Iraq. Obviously not the first inception of the wheel, it is the first we can place a date and origin on.
The true beginnings of the wheel date back possibly as far as the Paleolithic era (15,000 to 750,000 years ago). This wheel was nothing more than a log, laid alongside others, which was placed beneath a load to be moved. The main problem with this method of transportation was that many rollers were required, and care was required to insure that the rollers stayed true to their course. It was also a slow and labor intensive activity and not very efficient. Whereas, man always likes to make life easier for himself. I think we can agree on that.
DRIVING FROM DRINKING
It was around 3000 B.C. that the first goblets appeared. Clay goblets are normally made by throwing them on a wheel in two partsófirst the bowl, then the stem (including the foot). This makes for a far more smooth and regular shape than could be achieved by manual coiling, and since the oldest surviving goblets bear the telltale signs of wheel manufacture, it is plausible that wheels were used for pottery before they were used for transportation. For that matter, itís conceivableóthough admittedly an improbable speculation, that the wheel was invented for the express purpose of making goblets. Be that as it may, it is virtually certain that historically, the preferred way to make goblets was to throw them.
If the wheel was indeed invented for the convenience of potters, the question then becomes how it came to be used for transportation; clearly, whichever use appeared first, the other quickly followed. In all probability, the first potters wheel might have been an up-ended cart.
Up till now, it is still a mystery as to who invented the wheel and when the wheel was invented. According to archaeologists, it was probably invented in around 8,000 B.C. in Asia. The oldest wheel known however, was discovered in Mesopotamia and probably dates back to 3,500 B.C.
.Based on diagrams on ancient clay tablets, the earliest known use of this essential invention was a potterís wheel that was used at Ur in Mesopotamia (part of modern day Iraq} as early as 3500 BC. The first use of the wheel for transportation was probably on Mesopotamian chariots in 3200 BC. It is interesting to note that wheels may have had industrial or manufacturing applications before they were used on vehicles.
A wheel with spokes first appeared on Egyptian chariots around 2000 BC, and wheels seem to have developed in Europe by 1400 BC without any influence from the Middle East. Because the idea of the wheel appears so simple, itís easy to assume that the wheel would have simply "happened" in every culture when it reached a particular level of sophistication. However, this is not the case.
The great Inca, Aztec and Maya civilizations reached an extremely high level of development, yet they never used the wheel. In fact, there is no evidence that the use of the wheel existed among native people anywhere in the Western Hemisphere until well after contact with Europeans.
LIKELY STAGES OF DEVELOPMENT
The following steps and developments probably took place to invent a functioning wheel, more or less in this order as man realized that heavy objects could be moved easier if something round (e.g. a tree log) was placed under it and the object rolled over it. This could have been discovered by accident.
Humans also found a way to move heavy objects, with an invention archeologists call the sledge. Logs or sticks were placed under an object and used to drag the heavy object, like a sled and a wedge put together.
STEP ONE: Early man placed rollers beneath heavy objects so that they could be moved easily. Humans thought to use the round logs and a sledge together.
STEP TWO: Early men began to place runners under a heavy load, which they discovered would make it easier for the load to drag. This was the invention of the sledge.
Wooden pegs were used to fix the sledge, so that when it rested on the rollers it did not move, but allowed the axle to turn in-between the pegs, the axle and wheels now created all the movement. These were the first carts.
Improvements to the cart were made. The pegs were replaced with holes carved into the cart frame, the axle was placed through the hole. This made it necessary for the larger wheels and thinner axle to be separate pieces. The wheels were attached to both sides of the axle.
STEP THREE: Men began to combine the roller and the sledge. As the sledge moved forward over the first roller, a second roller was placed under the front end to carry the load when it moved off the first roller. A model of a sledge with such rollers is in the Smithsonian Institution. Humans used several logs or rollers in a row, dragging the sledge over one roller to the next.
STEP FOUR: Soon, men discovered that the rollers which carried the sledge became grooved with use. They soon discovered that these deep grooves actually allowed the sledge to advance a greater distance before the next roller was needed, a simple form of gearing, or mechanical advantage. In addition, the sledge moved more easily.
With time the sledges started to wear grooves into the rollers and humans noticed that the grooved rollers actually worked better, carrying the object further. This was simple physics, if the grooves had a smaller circumference than the unworn parts of the roller, then dragging the sledge in the grooves required less energy to create a turning motion but created a greater distance covered when the larger part of the log roller turned.
Another theory involves simply putting pins down through the corners of the sledge, utilizing two pins on the end of each roller, to hold the rollers in place. The latter theory provides a logical transition to the grooved roller, by the simple fact that friction caused by the underside of the sledge on the rollers would wear grooves in the rollers over time. In response to this, the roller may have been made thinner in the middle, and larger ends. At this point in the evolution of the wheel, we begin to see distinct, solid wheels connected by an axle-tree replacing the primitive roller.
As with the simple roller, there was a significant flaw in the design of the axle-tree and solid wheel configuration. When a cart with wheels of this design is towed, cornering is an awkward, sometimes dangerous maneuver. In a sharp turn, the inside wheels are dragged around the turn, with the potential of overturning the sledge. One solution to this issue was found in the fixed axle, with wheels that rotated freely around the axle. Arranged as such, the wheels were free to rotate independently when cornering, allowing the inside wheel to turn more slowly while the outside wheel sped up. This leap forward in technology necessitated alteration of the wheel itself as well. Solid wheels were developed, with a hole bored through the center for the axle.
STEP FIVE: The rollers were changed into wheels. In the process of doing so, wood between the grooves of the roller were cut away to form an axle and wooden pegs were fastened to the runners on each side of the axle. When the wheels turn, the axle turned too in the space between the pegs. The first wooden cart was thus made. The move from solid log, to axle, was probably just as important as the discovery of the log as a roller. The log roller had become a wheel and an axle.
Next the fixed axle was invented, where the axle does not turn but is solidly connected to the cart frame. Only the wheels did the revolving by being fitted onto the axle in a way that allowed the wheels to rotate. Fixed axles made for stable carts that could turn corners better.
STEP SIX: A slight improvement was made to the cart. This time, instead of using pegs to join the wheels to the axle, holes for the axle were drilled through the frame of the cart. Axle and wheels were now made separately. By this time the wheel can be considered a complete invention.
The wheel was furthered improved on later by the Egyptians, who made wheels with spokes, which could be found on Egyptian chariots of around 2000 BC. Over in Ancient India, chariots with spoked wheels dating back to around 1500 B.C. were also discovered. The Greeks too, adopted the idea of wheel-making from the Egyptians and made further improvements to it. Later, during the time of the Roman Empire, the Romans too engaged themselves in wheel-making and produced the greatest variety of wheeled vehicles. They had chariots for war, hunting, and racing, two-wheeled farm carts, covered carriages, heavy four-wheeled freight wagons and passenger coaches.
However, even in Europe, the wheel evolved little until the beginning of the nineteenth century. However, with the coming of the Industrial Revolution the wheel became the central component of technology, and came to be used in thousands of ways in countless different mechanisms.
IMPROVING THE WOODEN WHEEL
Two types of solid wheels are shown here. The first is a solid cross section of a tree. The main shortcoming of this wheel is the fact that its design, by nature, is flawed. In a cross section of a tree, the strength of the grain of the wood is not utilized, as with a plank cut lengthwise from a tree. This causes the wheel to split easily, as seen in the display wheel (see the lead picture at top of page). In order to strengthen the solid wheel, the strength of the tree's grain was utilized by building wheels from planks. Such wheels were typically made from three pieces. These three pieces were pinned or banded together, with the axle hole bored through the center piece.
The next evolutionary step for the wheel was the advent of the spoke. The spoke was developed in an attempt to lighten the wheel. The first attempts at wheel lightening resulted in solid wheels with gaps between the planks, leaving rough spokes. From this design stemmed the idea of the spoked wheel, consisting of a hub-with an axle hole, felloes (a felloe is one section of the rim of a wheel) and the spokes themselves. Note that the felloes of the Persian cart wheel are not carved to shape with the wheel, rather one side is left straight to save time and labor. This wheel was crude, but it was lighter and stronger than the solid wheel, and it used less material.
As the need to move faster, and with greater ease drove man further from his home, for hunting and conquering purposes, wheels became lighter. Another reason wheels became lighter, was scarcity of materials. In order to make wheels lighter, and use less material, spokes became narrower, as did the rims of the wheel. The felloes were slimmed down by carving both sides to shape, eliminating a considerable amount of wood from the wheel, as seen in the Egyptian chariot wheel. This wheel, while lighter and faster, bore the disadvantage of requiring a skilled wheelwright to build it. The Greeks are credited with introducing the cross-bar, or H-type, wheel as an efficient, easily built wheel. The well to do used the spoked wheel, and the common, less wealthy population used the cheaper cross-bar wheel.
When wheel making became an endeavor requiring a skilled artisan, measures were required to protect the wheel from damage. Protective sheathing was utilized for this purpose. These covers on wheels, known today as tires, began as such simple substances as leather, iron, wood, and later, rubber. The leather tire on the solid constructed wheel is held on with nails, and offers a minimal amount of protection to the wheel. The tire serves as a buffer from damage to the wheel. Should the vehicle encounter a jagged rock, or other impediment, the tire, which can be replaced with relative ease, will be damaged instead of the wheel, prolonging the life of the wheel.
Iron tires were introduced later, and proved to create a more durable protective surface for the wheel. The first iron tires were pieced together iron strips laid end to end and nailed or riveted to the wheel. The fact that such tires were piecemeal would suggest a lack of structural integrity, and a fairly regular schedule of maintenance. The iron shod wheel featured in our display, however, is clearly built with a single, continuous band of iron. Early attempts at placing a band of iron around a wheel were ill-fitting, being larger than the wheel, and requiring rivets to hold the tire in place. Our wagon wheel, with a well fitting, continuous iron tire, is the result of taking an iron hoop slightly smaller than the wheel and heating the iron until it expands enough to girdle the wheel. As the tire cools, it shrinks, creating a powerful grip on the wheel. The strength of this grip was almost all that was needed to hold the wheel together, allowing for elimination of materials, and thus weight, from the wheel.
G.F. Bauer registered the 1802 patent on the first wire tension spoke, but it was not until 1869 that W.F. Reynolds and J.A. Nays incorporated them in their Phantom Veloce. This wire spoke consisted of a length of wire threaded through the rim of the wheel and secured at both ends to the hub. Over the next few years, this wire spoke evolved into the round tension spoke we see on bicycles today. The first major use of such spokes is credited to James Starley, inventor of the Ariel and other bicycles. The main advantage of the tension spoke is that it allows slight flexing of the spokes while retaining the structural shape of the wheel. The functional difference between tension spokes and wooden spokes is that the weight of the rider and the frame is suspended from the top part of the rim by tension spokes, where the wooden spokes provides support from the ground up. The tire placed around the first tension-spoked wheels was typically hard rubber, as displayed on our highwheel and safety bicycles.
THEN CAME THE TYRE
The bicycle also claims responsibility for the pneumatic tire, which was first patented as a concept in 1845 by R.W. Thompson, of England, although he never produced a single one. In 1888, John Dunlop, a Scottish veterinarian, improved upon and patented the pneumatic tire, earning true credit for it (Dunlop is also credited with coining the term "pneumatic"). Dunlop reportedly developed the air filled, pneumatic tire to ease the headaches his young son suffered when riding his tricycle, which rode on hard rubber tires. Dunlop's tires quickly became the most sought after tire for bicycles, providing the smooth, high speed ride that replaced hard rubber as the tire of choice for serious cyclists. Within a few years, virtually all new bicycles sold were equipped with pneumatic tires.
The early pneumatic car tire, in solid white, was far different from today's 50,000-mile tires. Constructed from white, carbonless rubber, the tire had a maximum life expectancy of around 2000 miles. And a hard 2000 miles those were. On average, an automobile tire lasted around 30 or 40 miles before it needed repair. Punctures, the tire coming off the wheel, and the tube being pinched accounted for the majority of blow-outs, which required that the tire be removed from the wheel, and a spare placed on the wheel. In order to complete a car trip of any length, a number of tires, which were strapped to running boards, roofs, etc, were required. At the end of 2000 miles, there was usually not much of the tire left, and its remains were discarded.
Asserting prevalence in the 1920's, the disc wheel is the next evolutionary step in wheel technology, despite the fact that the steel disc wheel is reminiscent of the solid wheel. While the disc wheel has its shortcomings, it offers many advantages over spoked wheels, the foremost being cost efficiency. While building a spoked wheel was a difficult process, one requiring a skilled wheelwright, a disc wheel was relatively simple to build. The rim could be rolled out of a straight strip of metal, and the disc itself could be stamped from sheet metal in one easy motion. The two components were welded or riveted together, and the resulting wheel was one that was relatively light, stiff, resistant to damage, easily produced in mass quantities, and most important, cheaply produced.
Further advances in metallurgy and plastics have allowed the relatively solid disc wheel to be whittled away to produce extremely lightweight, strong spoked wheels. Just in the manner that the spoked wheel first evolved with advancing wheel technology, the three modern wheels on display - motorcycle, bicycle, and automobile - were created through advanced technology providing metals and plastics that are both very lightweight, and extraordinarily strong. As materials become lighter and stronger, less material is needed to make a wheel, creating a much lighter wheel than ever before, allowing for more speed and ease of use. This progression, from a solid disc to a spoked wheel, is a contemporary version of the same progression from many years ago, with modern components allowing the advance. It is a fitting end to this display that the emerging technology is simply a cyclic progression, coming around, much like a wheel, full circle, leaving us to only wonder, what will come next.
Wheels are used in conjunction with an axle, either the wheel turns on the axle or the wheel is rigidly attached to the axle which then turns in bearings in the body of the vehicle. The mechanics are the same in either case.
The low density of the friction (compared to dragging) is explained as follows:
the sliding distance is reduced, because the sliding takes place between the wheels and the axles or between the axles and the bearings
the coefficient of kinetic friction μ for the sliding friction is less
If dragging a 100 kg object for 10 m along a surface with μ = 0.5, the normal force on Earth is 980 N and the work done (required energy) is 980 ◊ 10 ◊ 0.5 = 4900 joules.
Now give the object 4 wheels. The normal force between the 4 wheels and axles is the same (in total) 980 N, assume μ = 0.1, finally the most important factor is the wheel diameter (1000 mm) and axle diameter (50 mm). Now while the object still moves 10 m the sliding frictional surfaces only slide over each other a distance of 0.5 m. So work done is 980 x 0.5 x 0.1 = 49 joules.
Additional energy is lost at the wheel to road interface (rolling friction), but it is deformation loss which can be very small. An example would be train wheels on rail tracks). The tradeoff is that a wheeled object in motion carries more momentum than dragging, and thus require an external force in the opposite direction in order to stop the object or change its direction, for example, such as brakes.
The invention of the wheel turned out to be of great importance not only as a transportation device, but for the development of technology in general, important applications including the water wheel, the cogwheel (see also antikythera mechanism), the spinning wheel, the astrolabe or torquetum. More modern descendents of the wheel include the propeller, the jet engine, the flywheel (gyroscope) and the turbine.
The central importance of the wheel also resulted in its becoming a strong cultural and spiritual metaphor for a cycle or regular repetition (see chakra, reincarnation). In July 2001, the wheel was the object of an innovative, but non-inventive, patent as a "circular transportation facilitation device". The patent was obtained by John Keogh, a lawyer from Melbourne, Australia, with the declared intention of demonstrating the unfairness and inaccuracy of the modern patent system.
Today, we see that the wheel has indeed undergone a drastic transformation from the very simple one made of wood to one with pneumatic rubber tyres fitted to machined alloy castings, or spun rims on machined centers, at we see today on circuit racing vehicles and land speed record cars.
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