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will vary with time, since with respect to this second frame the body is moving—i.e., is adopting successive positions in time.
The classical Galilean transformations had for their object to tell us exactly how these co-ordinates would vary when we passed from one Galilean frame to another. As it was always assumed by classical science that time was absolute, the same for all systems, the only co-ordinates susceptible of variation as we changed frames were the space co-ordinates
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