I'm a non-physicist, so I may be completely confused about this, but:
Isn't acceleration or rotation *always* defined or described in
relationship to something that is not accelerating or not rotating (or
acceleratig or rotating at a different rate) with respect to the thing
being defined or described? If that is so, how can we specify for any
frame (F1) whether it is rotating or non-rotating, unless we have some
outside-that-frame referent (F2) for it? And then, by what means can we
specify which of those frames (F1 or F2) is at rest and which is in
motion, as, it seems to me, your statement implies. Stated differently,
motion of a frame seems to me to be observable only if the observer is not
on the frame being observed as being in motion. How, then, can anyone say
(define, describe, specify) which is rotating and which is non-rotating,
since those are specified only relationally?
Lloyd Eby
leby@nova.umuc.edu