??? You say that's not true at all an then say exactly what I just stated.
On Nov 8, 2010, at 4:10 PM, LaMontagne, Bob wrote:
you only make measurements in the frame you are in.
That's not true at all!
There is an idealized notion of an "observer" who is "in" a single
reference frame ... but those observers don't call the shots. In
my capacity as principal investigator, I can hire hordes of such
observers and assign them to many different reference frames.
Consider the aforementioned "scale on the wall of a rotating cylinder".
The scale reads some number, and all observers agree on the number,
but my *interpretation* of that number in verrry different, depending
on whether I am using a rotating reference frame or a non-rotating
reference frame ... or using both and switching back and forth. It
is very common to find that part of the problem is easier in one frame
and another part is easier in another frame, so I use measurements in
both frames and convert them as necessary. The conversion formulas
are well known.
For example; It is absolutely standard procedure, even in the most
introductory course, to solve part of a dynamics problem in the CM
frame and then to re-express the results in the lab frame.