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I read that in the 1800s people used to refer to "heavy riders" and "light riders" as being people who rode heavier or lighter than their actual weight. They would weigh horse and rider separately, and then weigh them together (with the rider mounted on the horse). If the combined weight was less than the separate weights added together, the rider was considered a "light rider", and if the combined weight was greater than the sum of the separate weights, the rider was a "heavy rider". It seems to me that this theory defies the laws of physics, but perhaps there is another factor that I have not considered. Can you tell me please if this is possible (that the sum of two weights can differ from the weight of the sum. thank you!
- Jenny Grainger (age 45)
Wellington, New Zealand
According to the latest theories, the answer is no.
Well, just to be pointlessly picky, the energy (and hence gravitational mass) of a combined system includes both the energies of the parts and the energies of their interactions. If you were talking about protons and neutrons, then it would be noticeably true that the combined weight is a bit different from the sum of the weights. Needless to say, such effects are utterly negligible for your example. Mike W.
(published on 05/28/12)
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