Re: Kinds of Mass

[Michael Edmiston <edmiston@BLUFFTON.EDU>]

In class, I still talk about the question of whether inertial mass and
gravitational mass are equivalent because I am under the impression
this is still a legitimate and ongoing area of physics research.
 However, I admit I might be out of date on this.  It seems like I
read, in the past year or so, of ongoing experiments in this area.
 However, the last time I thought I read something "just last year,"
and then finally found the journal article, I discovered I had actually
read it about 6 years ago.  Geesh, it's terrible what aging and being
busy do to the memory.

Does anyone on the list have recent experience/knowledge to bring the
rest of us up-to-date on whether people are still doing experiments to
test the sameness of inertial and gravitational mass?

Michael D. Edmiston, Ph.D.              Phone/voice-mail:       419-358-3270
Professor of Chemistry & Physics        FAX:                    419-358-3323
Chairman, Science Department            E-Mail                  edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817



-----Original Message-----
From:   Richard Tarara [SMTP:rtarara@SAINTMARYS.EDU]
Sent:   Friday, November 12, 1999 3:09 PM
To:     PHYS-L@lists.nau.edu
Subject:        Re: Kinds of Mass

Well, if it looks like a duck, walks like a duck, and quacks like a
duck........

I guess I don't understand why we hold onto the dual nomenclature.  Yes
the
conceptual origins suggested there might be a difference, but it seems
that
the experiments are pretty convincing that inertial and gravitational
mass
are identical.  Why continue to speak of these separately?  Are they
ever
different?  For example, what is the gravitational interaction between
two
masses moving parallel to each other (relative velocities zero).  Would
one
use the rest masses or the relativistic masses in GMm/R^2 (realizing
that
true relativists would probably never use the Newtonian formulation)
and
does it matter in terms of the inertial/gravitational nomenclature?

Rick

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----- Original Message -----
From: Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Friday, November 12, 1999 12:21 PM
Subject: Re: Kinds of Mass


> Different conceptual origins of inertial and gravitational masses
> are clear to me. But not the nuance according to which one
> should also recognize two kinds of gravitational masses: active
> and passive. (Perhaps it is time that I should attempt to read the
> classic WMT text "Gravitation."). If Newton's third law is
> valid, for two mutually attractive bodies, then how do we
> decide which object is active and which is passive? Thanks
> for a clear summary.
>
> Peter Vajk wrote:
>
> > Several recent messages have talked about distinctions
> > between inertial mass and gravitational mass, etc.
> >
> > For an excellent discussion of these issues,  see Wheeler, Misner,
> > and Thorne's massive and classic text "Gravitation."
> >
> > There are three conceptually different masses used in physics"
> >
> > Inertial mass  -- this is the coefficient in F = ma.
> >
> > Active gravitational mass -- this is that property of an object
which
> > DOES the attractING in Newton's Law of Universal Gravitation,  or
which
> > acts as the source term in Einstein's Gravitational Field
Equations.
> > Passive gravitational mass -- this is that property of an object
 which
> > IS attractED in Newton's Law of Universal Gravitation.
> >
> > A priori,  there is no logical NECESSITY for these three to be the
> > same.  Galileo's virtual Leaning Tower experiment,  however,  shows
(or
> > could show,  with the metrology available to Galileo) that the
RATIO of
> > Passive to Inertial mass is the same for bodies of different sizes
or of
> > different compositions within 1 part in 100 or so.  The Eotvos
> > Experiment (circa 1900) showed an accuracy of a few parts in 10,000
or
> > so.  The higher accuracy results from modern measurements on
motions
> > of satellites in orbit -- don't have a handy reference on this,
 but
> > Fairbanks's group at Stanford University was pursuing this some 20
or
> > so We can then use Newton's Third Law (if it is valid) to show that
the
> > ratio of Active to Passive gravitational masses is the same for
> > different sizes and compositions of objects to similar accuracies.
> >
> > If these three masses are really the same,  or are inherently
> > proportional to each other regardless of composition,  size,
 density,
> > etc., etc.,  then the uniformity of acceleration in a given
> > gravitational field follows at once,  and Einstein's representation
of
> > gravitation by a purely geometric  theory is possible,  with the
motion
> > of particles in a gravitational field represented by geodesics in
the
> > warped four-geometry of space-time.  (The Principle of
Equivalence.)
> > But WHY these three should be equivalent to one another,  and WHY
these
> > are related to the chemistry concept of mass ("a measure of the
total
> > amount of material") is as yet an unsolved question.