Patrick Cassidy wrote:
> Just a comment on one point in Ingvar's last note:
>
> On mass:
>> 3. You write: "and in middle school we learn that each kind of such
>> particles has a mass which can be computed as the sum of the mass of
>> its constituents." Not EACH kind of particle. Photons and neutrinos
>> have no mass.
>>
> Photons have relativistic mass, though no rest mass; neutrinos actually have
> a very small rest mass (according to the latest info I have). The "mass" we
> measure is relativistic mass, and I don't think any distinction is required
> in the units ontology (though it would be in an ontology of physics).
> Relativistic mass is a very useful concept because it provides a simple
> definition of 'physical object' as an Object (primitive concept) that has
> some mass; that would include photons and any other fundamental particles
> that have relativistic mass. (01)
I love these little nit-picks if I only had the time :) (02)
Actually I said "each kind of SUCH particles" (that are the constituents
of matter, namely atoms and molecules, as taught in elementary school)
Those constraints I made precluded photons and neutrinos, also quarks
and leptons, hadrons whether mesons, baryons, positrons or even electrons,
regardless of whether they have a rest mass or not. (03)
-Gunther (04)
--
Gunther Schadow, M.D., Ph.D. gschadow@xxxxxxxxxxxxxxx
Associate Professor Indiana University School of Informatics
Regenstrief Institute, Inc. Indiana University School of Medicine
tel:1(317)423-5521 http://aurora.regenstrief.org (05)
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