Re: [Phys-l] Teaching Special Relativity

[Brian Whatcott <betwys1@sbcglobal.net>]

I read Jack's example, and came across this footnote, which seems to 
illustrate
the measurement of a length by taking non-simultaneous measures of marks 
on a rod.
This was my understanding of Moses' use of the proper length idea.

[from the reference wiki:]

Note 2: Proper length has also been used in a more restricted sense to 
help with discussions of length contraction by textbooks, where it is 
defined as the length of an object when measured by someone at rest 
relative to that object.

Jack Uretsky wrote:
> Hi all-
>  	See
> http://en.wikipedia.org/wiki/Proper_length
> as an example of the use of the word "proper" in ordinary relativistic 
> parlance.  "Proper" and "invariant" are, for all practical purposes
> the same.
>  				Regards,
>  					Jack