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Efficiency, ratio of the useful work derived from a machine to the energy put into it. The mechanical efficiency of a machine is always less than 100%, some energy being lost as heat in friction. A typical gasoline engine may have a thermal efficiency of only 25%, a steam engine, 10%.

See also: Energy.

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21st Century Webster's Family Encyclopedia21st Century Webster's Family Encyclopedia - Dream to Eijkman, Christiaan