Re: [Phys-l] Teaching Special Relativity

[Brian Whatcott <betwys1@sbcglobal.net>]

Moses Fayngold wrote:
> ... Consider a solid rod of constant proper length l(0). If you are in the rest frame K0 of the rod, and you want to measure its length, you can do it by first marking its end-points. And it is not necessary
> that you mark them simultaneously in K0. You can mark one end now (at a moment t1) and the other end later (at a moment t2) in K0, and then quietly measure the distance between the marks. We can even consider such measurement as a possible operational definition of proper length.
> ...Moses Fayngold,
> NJIT

Ouch!    I read JD's objection to this assertion in particular, and 
couldn't help but notice that the MF description sounded like the method 
used in Paris for quite a while with their standard platinum meter bar.
I evidently don't even see how this varies substantially from the 
current method of counting cycles of an atomic line along such a standard.

Brian W