| Any single force is only one aspect of a mutual interaction between two bodies | Cambridge UK: Cambridge University Press |
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| I Bernard Cohen Peter M | Hannah, J, Hillier, M J, Applied Mechanics, p221, Pitman Paperbacks, 1971• Metaphysics Research Lab, Stanford University |
When the mass varies due to accretion or ablation, [an alternate equation explicitly accounting for the changing mass] should be used.
11| "On the use and abuse of Newton's second law for variable mass problems" | I]t is essential to deal with the same set of particles throughout the time interval[ |
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| Quoting Newton in the Principia: It is not one action by which the Sun attracts Jupiter, and another by which Jupiter attracts the Sun; but it is one action by which the Sun and Jupiter mutually endeavour to come nearer together | ] Consequently, the mass of the system can not change during the time of interest |