wheel window: see rose window.

wheel bug: see assassin bug.

wheel and axle, simple machine consisting of a wheel mounted rigidly upon an axle or drum of smaller diameter, the wheel and the axle having the same axis. It is fundamentally a form of lever, the center common to both the wheel and the axle corresponding to the fulcrum, the radii of the two parts to the arms. The effort (applied to the wheel) needed to overcome the resistance (acting upon the axle) is relatively small. The mechanical advantage gained by the use of the wheel is equal to the ratio of the radius of the wheel to the radius of the axle. The wheel and axle is not as efficient as the lever, since a part of the effort must be used to overcome the resistance of friction. In common use, a crank or handle often takes the place of the wheel. Applications of the wheel and axle are numerous in everyday life; examples are the steering wheel of an automobile, the doorknob, and the windlass. The effort is applied through a greater distance than is the resistance, but this effort is applied conveniently in a circle. In the treadmill, the windmill, and the waterwheel, the wheel and axle led the way to the utilization of power in modern machinery. Clockmakers were pioneers in devising ways of transmitting and controlling power by the use of the wheel and axle.

wheel. Through the many millennia of the Paleolithic period and the Neolithic period no use of the wheel was known to humans. Its use was not known to the Native Americans until the Europeans introduced it. In the Old World it came into use in the Bronze Age, when oxen and horses were first used as draft animals and wheeled vehicles were devised. Wheels for vehicles were at first solid wooden disks; spoked wheels were introduced c.2700 B.C. The potter's wheel was invented in the Bronze Age, earlier pottery being made, like that of the Native Americans, without the use of the wheel. See gear; tire; wheel and axle.

water wheel, device for utilizing the power of flowing or falling water. The Norse wheel is the oldest type known. Despite its name it probably originated in the Middle East, where the swift stream required by this type of wheel is common. The Norse wheel has a vertical shaft directly connected at the top to a millstone; the lower end of the shaft, with vanes or paddles attached, dips into the flowing stream. In the 1st cent. B.C. a horizontal shaft came into use; the wheel attached to it had radial vanes around its edge. Among the early forms of this wheel are the overshot wheel, used where water falls from a height, striking the vanes from above; the breast wheel, employed where the height of the water is less than the height of the wheel so that the water strikes the wheel about midway; and the undershot wheel, usable where the water flows more or less on a level but with a swift current and strikes the vanes on the under part of the wheel. One of the first uses of the steam engine was to drive a pump that raised water into a millpond whose spillway drove a water wheel. Today the water wheel has been largely replaced by the turbine. See hydraulic machine.

Ferris wheel, amusement park ride. It consists of a power-operated wheel that is about 50 ft (15 m) in diameter. It has two rims that are parallel to and equidistant from the shaft about which the wheel rotates. Between the rims there are a number of seats or enclosed cars that carry passengers. George W. G. Ferris, a U.S. engineer from Galesburg, Ill., designed and built the first such wheel for the World's Columbian Exposition held in Chicago in 1892. This wheel was 250 ft (76 m) in diameter and carried 36 cars with a seating capacity of 40 passengers each; its total weight was 220 tons. The world's largest Ferris wheel is that in Singapore (2008), which rises to 541 ft (165 m). Other large Ferris wheels include those in London, England (443 ft/135 m), and Yokohama, Japan (344 ft/105 m); the largest in the United States is the Texas Star in Dallas, at 212 ft (65 m). Ferris wheels may be found at many exhibitions, fairs, and carnivals.

In Gothic architecture, a decorated circular window, often glazed with stained glass, that first appeared in mid-12th-century cathedrals. It was used mainly at the western end of the nave and the ends of the transept. The bar tracery of a High Gothic rose window consisted of a series of radiating forms, each tipped by a pointed arch at the outside of the circle. The rose windows of Notre-Dame de Paris are particularly noteworthy. In later Flamboyant-style tracery, the radiating elements consisted of an intricate network of wavy, double-curved bars.

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Device for igniting the powder in a firearm such as a musket. Developed circa 1515, the wheel lock struck a spark to ignite powder in the pan of a musket by means of a holder that pressed a shard of flint or a piece of iron pyrite against an iron wheel with a milled edge; the wheel rotated and sparks flew. The principle was used in the design of the flint-and-wheel cigarette lighter. Seealso flintlock.

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Circular frame of hard material capable of turning on an axle. Wheels may be solid, partly solid, or spoked. The oldest known wheel was a wooden disk of planks held together by crosspieces. A pottery wheel or turntable was developed circa 3500 BC in Mesopotamia. The spoked wheel appeared circa 2000 BC on chariots in Asia Minor. Later developments included iron hubs that turned on greased axles. Perhaps the most important invention in human history, the wheel was essential to developing civilizations, and has remained essential to power generation, transportation, industrial manufacturing, and countless other applications.

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Early machine for turning textile fibre into thread or yarn, which was then woven into cloth on a loom. The spinning wheel was probably invented in India, though its origins are unclear. It reached Europe via the Middle East in the Middle Ages. The improvement of the loom in 18th-century England created a yarn shortage and a demand for mechanical spinning. The result was a series of inventions that converted the spinning wheel into a powered, mechanized component of the Industrial Revolution (see drawing frame; spinning jenny; water frame).

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In Tibetan Buddhism, a mechanical device used as an equivalent to the recitation of a mantra. The prayer wheel consists of a hollow metal cylinder, often beautifully embossed, mounted on a rod and containing a consecrated paper bearing a mantra. Each turn of the wheel by hand is considered equivalent to orally reciting the prayer. Variants to the handheld prayer wheel are large cylinders that can be set in motion by hand or attached to windmills or waterwheels and thus kept in continuous motion.

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