Re: Ken, need help with this
From: Pmb (pmb_phy_at_yahoo.com)
Date: 11/02/04
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Date: 2 Nov 2004 07:31:48 -0800
dynamics@vianet.on.ca (Ken S. Tucker) wrote in message news:<2202379a.0410291805.49485afb@posting.google.com>...
> pmb_phy@yahoo.com (Pmb) wrote in message news:<2a7af61a.0410290723.1330f798@posting.google.com>...
> > Creighton Hogg <wchogg@hep.wisc.edu> wrote in message news:<Pine.LNX.4.44.0410281339360.20420-100000@erodium.hep.wisc.edu>...
> > > On 28 Oct 2004, Pmb wrote:
> > >
> > > > Tom Roberts <tjroberts@lucent.com> wrote in message news:<xDWbd.9802$Rf1.7313@newssvr19.news.prodigy.com>...
> > > > > Pax wrote:
> > > > > > [...]
> > > > > > Strange, it seems a massless particle can have no velocity, is incapable
> > > > > > of momentum, and has no energy.
> > > > >
> > > > > When you assume Newtonian mechanics, and apply it to massless particles,
> > > > > you get nonsense.
> > > >
> > > > p = mv is not Newtonian mechanics. Its mechanics - period. m =
> > > > constant is Newtonian mechanics. m = m(v) is relativistic mechanics.
> > > > But p = mv is a definition and as such it doesn't belong to a
> > > > particular theory. E.g. v_x = dx/dt is neither Newtonian or
> > > > relativistic. It just is. F = dp/dt isn't Newtonian and it isn't
> > > > relativistic - its just is.
> > >
> > > Language is determined by the majority. Any particle physicist I know
> > > would look at you funny if you said p = mv applies to photons.
> > > Relativistic mass is not used in the majority of papers in particle
> > > physics.
> >
> > Not all relativity is particle physics. Had you asked a particle
> > physicist what the half life of a free neutron was he'd most likely
> > say "15 minutes". However that is the proper lifetime and not the
> > actually life time. A particle physicists would ot deny the reality of
> > time dialtion. Particle physicist have their own terminology and its
> > taylored to their work. Particle physicists don't study relativity -
> > they use it. A particle physicist could accelerate a small capacitor
> > to the speed of light but a relativist can describe its energy of it.
> >
> > Particle physicists study the *intrisic* properties of particles.
> > Proper lifetime is such a quantity. But they simplify it for their
> > use.
> >
> > Consider cosmologists on the other hand. They will use terminology in
> > a different way - one is not right and the other wrong - they just
> > choose to use different terminology - However if you were to ask
> > someone like Alan Guth if light has mass then I'm 100% positive he'd
> > say - Yes!
> >
> > Most relativity texts that I have use relmass but simply refer to it
> > as mass. Wolfgang Rindler defines mass as the m in p = mv (in his new
> > SR/GR text pub in 2001) as do most relativists that I know of - Even
> > Schutz does in his new book. In his GR book he quite clearly states
> > that "rest mass" is not a fuction of speed whereas "inertial mass"
> > (what some call relativistic mass) is a function of speed.
> >
> > Pmb
>
> Thanks Pete
> nice essay.
> Ken
Your welcome Ken. I've been thinking alot about this lately, i.e.
about macroscopic bodies. Specifically bodies which are under stress,
i.e. which have external forces acting on them. A friend of mine lent
me Rindler's SR text which is very good on this topic. It was nice to
see that Rindler quite literally stated that E = gamma*m_o^c^2 was not
valid in general. It also occured to me that people like tom never
seem to think about, or discuss, anything except particles. And there
is more to relativity than particles.
Pete
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