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Energy Transformations

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Energy can be changed from one form to another.  For example, as water falls over a waterfall, its gravitational potential energy is first transformed into kinetic energy, then into thermal energy when it hits the ground.  Or the kinetic energy of the water stream could be transformed (1) into the rotational kinetic energy of a turbine shaft, then (2) into electricity by turning the shaft of a generator, then (3) into thermal energy by passing the electricity through a resistor, raising its temperature.  Finally, heat can be transferred from the resistor to the surrounding air, to warm a house.  

Figure 7
Energy transformation

A toaster uses electrical, mechanical, and thermal energy.