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Newton defined energy as a force which is is capable of moving things. Since then the concept of energy has often changed. At the beginning of the century Einstein introduced the equation e = mc˛. Apart from this equation there is another very well known scientific law - the first law of thermodynamics i.e. energy can neither be created nor destroyed - only transformed. Although energy doesn’t change its form does. For example gravity is a form of energy. In a plant powered by water, water through the force of gravity flows over large turbine wheels and produces electricity i.e. gravity was transformed in electricity. Electricity is transformed into light, light penetrates our eye and sets off a nerveimpulse. Here we are dealing with changes of forms of energy.