Re: Only some energy has mass?
From: Pmb (someone_at_somewhere.com)
Date: 12/06/04
- Next message: mmeron_at_cars3.uchicago.edu: "Re: Degradation of nuclear weapons"
- Previous message: Pmb: "Re: Only some energy has mass?"
- In reply to: Y.Porat: "Re: Only some energy has mass?"
- Next in thread: lvlus_at_hotmail.com: "Re: Only some energy has mass?"
- Messages sorted by: [ date ] [ thread ]
Date: Mon, 6 Dec 2004 02:08:36 -0500
"Y.Porat" <maporat@012.net.il> wrote in message
news:4e35159f.0412052253.cc65ef8@posting.google.com...
> dr_prometheus@yahoo.com (D.P.) wrote in message
news:<ccce5a0e.0412051959.4513708f@posting.google.com>...
> > lvlus@hotmail.com (TomGee) wrote in message
news:<cc2dde17.0412051229.3160f804@posting.google.com>...
> > > dr_prometheus@yahoo.com (D.P.) wrote in message
news:<ccce5a0e.0412040904.19eef48c@posting.google.com>...
> > > > macromitch@internetCDS.com (Mitchell) wrote in message news:<
> > > > You need to be careful to distinguish between "relativistic
> > > > mass" and "rest mass". The term "relativistic mass" is used
> > > > for pedagogical reasons in some introductory texts, but most
> > > > physicist do not find it to be a terribly useful concept, so
> > > > physicist nowadays generally talk about "rest mass". When we
> > > > give the mass of a particle, we almost always mean its rest
> > > > mass. The relationship between energy, momentum and rest
> > > > mass is E^2 = (m c^2)^2 + (p c)^2 where p is the momentum
> > > > and is given by gamma*mv for a massive particle and
> > > > gamma = 1/sqrt(1-(v/c)^2). As the mass of a particle with
> > > > finite energy goes to zero, it's velocity approaches the speed
> > > > of light and gamma diverges. However the product gamma*m
> > > > remains finite, so the momentum remains finite. The relation
> > > > between energy and momentum for a massless particle is then
> > > > E = p c. So increasing the energy of a photon would increase
> > > > its momentum, but not its (rest) mass.
> > >
> > >
> > > Well, congratulations, Mr./Ms. D.P., you have managed to repost the
> > > same argument of conformist physicists today, except that you don't
> > > quite have it down as to the difference between rest mass and
> > > invariant mass. You obviously think they are the same. The
> > > relativistic mass and the invariant mass have zero rest mass. When
> > > physicists refer to the mass nowadays, as I have been told, they mean
> > > the invariant mass since they have conspired to eliminate the R-mass
> > > because it does not conform to their expectations and causes trouble
> > > with their math constructs.
> > > TomGee 120504
> >
> > The above is nonsense.
> >
> > The rest mass and the invariant mass are, by definition, exactly
> > the same thing.
That is not quite the case. Differernt people use the terms differently.
E.g. In "Gravitation and Spacetime - 2nd Ed.," Ohanian and Ruffini the
authors use "rest mass" to refer to the proper mass of a single,
structureless, particle whereas they use the term "invariant mass" to refer
to the magnitude of the 4-momentum of a system of particles. The authors
believe it is a bad idea to use the term "rest mass" to refer to a system of
particles for which not all of the particles are at rest .... at least
that's what Ohanian tells me.
Pmb
- Next message: mmeron_at_cars3.uchicago.edu: "Re: Degradation of nuclear weapons"
- Previous message: Pmb: "Re: Only some energy has mass?"
- In reply to: Y.Porat: "Re: Only some energy has mass?"
- Next in thread: lvlus_at_hotmail.com: "Re: Only some energy has mass?"
- Messages sorted by: [ date ] [ thread ]
Relevant Pages
|
