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One strange thing about the One-Dimensional Motion with Constant Velocity model is that it is only applicable in the absence of interaction. Thus, in one sense all interactions are relevant to the model, because the presence of any interaction destroys its validity! In another sense, no interactions are relevant, because the model can only be used when you have assured yourself that any interactions acting on the system are either negligible or are perfectly balanced by opposing interactions so that they cancel out. Thus, there are no interactions present in the Law of Change for this model.