the Cartesian Quantity of Motion, mass multiplied by velocity (mv), is not conserved by falling bodies. And yet by doing, or even imagining, a very simple experiment, you can demonstrate that mass multiplied by the square of velocity (mv2) is conserved by such bodies. This quantity mv2 has certain properties of interest. For one, it measures the amount of work that a moving body is capable of doing. Work is something that has an absolute meaning, it is free from the problem of relativity that I mentioned a moment ago, a problem unavoidably shared by all theories that are founded upon the use
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