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d) All machines have an input, an output, and a transforming or modifying and transmitting device.

c) Machines that receive their input energy from a natural source, and transform it into mechanical energy are known as prime movers.

a) Windmills, waterwheels, turbines, steam engines, and internal-combustion engines are typical prime movers.

b) In these prime movers the inputs vary; the outputs are usually rotating shafts capable of being used as inputs to other machines, such as electric generators, hydraulic pumps, or air compressors.