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Rh converting so much of his energy of position into actual energy, just as a miller lets out a portion of his head of water in order to do some work by its means.

38. We have thus endeavoured to show that there is an energy of repose as well as a living energy, an energy of position as well as of motion; and now let us trace the changes which take place in the energy of a weight, shot vertically upwards, as it continues to rise. It starts with a certain amount of energy of motion, but as it ascends, this is by degrees changed into that of position, until, when it gets to the top of its flight, its energy is entirely due to position.

To take an example, let us suppose that a kilogramme is projected vertically upwards with the velocity of 19.6 metres in one second. According to the formula of Art. 28, it contains 19.6 units of energy due to its actual velocity.

If we examine it at the end of one second, we shall find that it has risen 14.7 metres in height, and has now the velocity of 9.8. This velocity we know (Art. 26) denotes an amount of actual energy equal to 4.9, while the height reached corresponds to an energy of position equal to 14.7. The kilogramme has, therefore, at this moment a total energy of 19.6, of which l4.7 units are due to position, and 4.9 to actual motion.