One million not out
Sir: I did not see the cover of The Spectator to which Derek Partridge referred (Letters, 16 September), but his claim that it is inap- propriate to use Einstein's famous equa- tion, E = mc2, when considering the energy expended by a batsman in hitting a ball, is incorrect. This equation, relating the ener- gy released by a system to its reduction in mass, is as true for the chemical reactions taking place in the batsman's body, which are the source of his energy, as it is for nuclear reactions, although the change of mass in a chemical reaction, being typically only one millionth the change of mass in a nuclear reaction, is usually ignored.
It is also incorrect to state that momen- tum is conserved when the batsman hits the ball. A large force is then applied to the ball for a short time, and, according to the rules of classical mechanics, this produces a change in the momentum of the ball. Only if the bat were to touch the ball very lightly without deflecting it, would the momentum of the ball be unaltered during the shot.
J.W. Humberston
Department of Physics and Astronomy, University College London, Gower Street, London WC1
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