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Water and Wind Power

As early civilizations searched for alternatives to animal and slave power , two natural sources of energy were widely harnessed : water and wind . These remained the principal means of driving machinery until the discovery of steam and electrical power , and today they are seen as important sources of renewable energy .

Wind power from windmills Windmills were a common sight throughout the world until they were gradually replaced by steam , combustion , and electric - powered engines . Post mills such as these could be turned to face the prevailing wind , their rotating sails driving machines to grind corn or , more rarely , to pump water for irrigation .

Water was an essential ingredient in early civilization : it was necessary for agriculture and for the growing towns . Early engineering focused on its transportation , and the flow of water in a river was soon recognized as a potential source of energy . By the time of the ancient Greeks , water was being used to drive simple machines . Wind power was also exploited in the ancient world by sailing boats .

Harnessing power

By the Middle Ages water and wind power were widely used to drive machinery . Water wheels - probably the earliest source of mechanical energy - powered the mills for grinding grain ; later they were also used for sawing wood and clothmaking . They became more sophisticated in design : vertically mounted wheels were made possible by a system of gears that transferred power to the mill . Overshot wheels - where water flows over the top of the wheel - began to replace the less efficient undershot design , which relies on a fast supply of water under the wheel ( see opposite ) . The first windmills were built in the 7th century , in Seistan , Persia . Unlike the familiar modern windmill , these had sails mounted on a vertical shaft : wooden blades , sometimes covered with cloth , were mounted on arms to catch the wind . The sails were fitted to a vertical axis driving a grinding stone .

Understanding hydraulics Wind and water power were also used in sawmills , clothmaking plants , and smelting metal furnaces . In the Islamic world the principle of the water wheel was developed into the noria , an undershot water wheel incorporating containers , which raised water for irrigation . In medieval China windmills inspired by the Persian design were used to pump water . Hydraulic power was widely used in water - powered machines throughout China and the Islamic world . Interest in water and wind power diminished during the 19th century as new forms of energy were exploited , but these natural powers are exciting interest again today in the search for renewable energy sources to replace non - renewable carbon - based fossil fuels . Wave power , tidal power , wind turbines , and hydroelectric plants are all increasingly being used around the world to generate electricity .

▷ Undershot water wheel

The earliest water wheels were slightly

submerged in a stream or river , in an

arrangement known as undershot . The flow of

water acts on paddles at the bottom of the wheel

to cause it to rotate , providing power for a mill .

▷Overshot water wheel Water

from a reservoir is directed through a channel

on to the paddles or blades on the rim of a wheel ,

making it rotate . More efficient than the undershot

water wheel , the overshot uses not only the flow of

water , but also the weight of water carried in

paddles on one side of the wheel .

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