Can the relationship [tex]\rho\,=\,\frac{h}{\lambda }[/tex] apply to all particles? If so then does [tex]\rho[/tex] still represent mv?

Yes.

I believe the relationship holds for all particles. ρ = mv for all particles except for a photon, for which mv doesn't make any sense...

If you're speaking about mass defined as

*proper mass* then you're. However, if you were speaking about mass as the more useful concept

**relativistic mass** (RM) then you'd be quite wrong.

Three texts which use RM are and calculate the mass of a photon are listed at:

http://home.comcast.net/~peter.m.brown/ref/relativistic_mass.htmHowever, in my opinion, you should have made it clear to Jeff which mass you had in mind.

Most SR texts which use the concept of relativistic mass readily define mass as m = p/c or as m = hf/c

^{2}. I created list of such textbooks and placed it in a webpage on my old website. The texts I have listed there are

**Relativity: Special, General and Cosmological** by Wolfgang Rindler,

*Oxford Univ. Press*, (2001).

**From Introducing Einstein's Relativity** by Ray D'Inverno,

*Oxford Univ. Press*, (1992).

**Special Relativity** by A. P. French,

*MIT Press,* (1968).

Those are just three. There are many else of course. These are just examples to illustrate the point.

Jeff: If you

*really* want to read an article which makes all of this quite clear then you can read the article I wrote. It was published in an Indian Journal and is now in a book too.

It's online at:

http://arxiv.org/abs/0709.0687Essentially the definition of inertial mass is quite simple and works in all possible situations of closed systems. I.e. mass is defined as the quantity

*m* such that

**p** =

*m***v** is a conserved quantity.