Water wheels harness the energy of moving water and have been used for millennia. They come in three types: horizontal, undershot, and overwheel, with the latter being the most efficient but also having a greater environmental impact.
Moving water has a lot of energy. Just six inches (15 centimeters) of running water can wash off a small car. A water wheel is an early and successful attempt to harness the energy of flowing water and make it available to man. A water wheel is a wheel with paddles or buckets attached to it. The water flows over the paddles or buckets, making the wheel move and allowing the transfer of energy to get the job done.
Waterwheels have been in use for millennia. Indeed, there is evidence that they were in use as early as 4000 BC. A Greek writer, Antipater, mentioned a water wheel in one of his works. Evidence of waterwheels can be found all over the world, including in Italy, India, China and the Americas. Regardless of where they are found, water wheels are commonly classified into three categories: the horizontal wheel, the redundant wheel, and the undershot wheel.
A horizontal wheel is thought to be the earliest form of water wheel. The wheel itself is usually placed on the floor of a mill or wherever it is used. The rapidly flowing water is then allowed to flow over it, hitting the blades and spinning the wheel. The revolving wheel is attached by a vertical axle to the upper millstone, which turns and grinds the wheel against a stationary lower millstone. This is the least efficient form of water wheel.
The undershot waterwheel is more efficient. This type of vertical wheel can be used where the landscape is flat. The force of the water pushes the blades under the wheel, causing it to spin. A variation of this type of wheel, although sometimes classified as a type in its own right, is the chest wheel. With this type of wheel, the water hits the buckets near or just above the center of the wheel.
Using about 63% of the energy of water, the overwheel is the most efficient type of waterwheel. A backshot wheel is a variation of this type. This vertical wheel uses the water pouring over the wheel to move it. Therefore, not only does the wheel move with the force of the water, but it also uses the force of gravity. Often, the water used to move these wheels will need to be dammed or diverted in some way. While this type of water wheel is the most efficient, its construction can also have a greater impact on the environment.
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