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At 11:46 +0800 5/10/07, <carmelo@pacific.net.sg> wrote:cut
So, the increase in elastic potential energy of a spring will effectively increase the spring's mass. The increase in gravitational potential energy of a muon will increase the muon's mass. If a muon is moving towards the earth, its mass would decrease. This seems to be John's conclusion. :-)I don't think so. The issue is, what is the system. In the case of gravity, it clearly is the "gravitor" and the "gravitee," if it is even possible to make that distinction. That is, the earth and the ball become more tightly bound to each other as the ball rolls down the incline, and so the mass of the earth *and* the mass of the ball, collectively decrease. It makes no sense to talk about either the mass of the earth *or* the mass of the ball individually changing, although it seems reasonable to me that to the extent one can torture