Special Relativity 72 GALILEAN RELATIVITY Galilean relativity is based upon our everyday experience, using the Newtonian notions of space and time. That is, we assume that time is the same for all observers. If we have two reference frames(denoted by xand x’) with the primed (’) moving at velocity urelative to the unprimed frame, the velocities of an observed object are related via: v = v’ + u (So here, assume that the unprimed observer is “at rest” and the primed observer is “moving” - this is the difference in the sign compared to what we had before.) Assuming that at t=0, x’=x (i.e., at t=0 our observers are at the same place), the coordinate transformationof an object is related via: Figure 1. Frame S is moving with velocity v in the x-direction. After a period of time thas elapsed, Frame S’ denotes the new position of frame S.