Consider single line motion. If an observer sees two objects, and one is seen moving say 50 m/s faster than the other, will all other observers measure the same velocity difference? The answer seems to be 'No' from the velocity addition formula of special relativity? Thus same velocity difference (i.e. same relative motion) is not preserved in special relativity. Does that not seem counter-intuitive? I understand no observed individual velocity can exceed c so we must give up simple classical velocity addition, but is there any intuitive reason why this must extend to the same velocity difference not being preserved? Intuitively - should relativity not preserve this relative value ? It would also seem from the velocity addition formula that the 50 m/s difference can be made to vary the full range between 0 and c, depending on the speed assigned to new observer. So there is no sense of any preservation of this relative value.