[hist-analytic] Materialism and mass as a unit of measurement
Roger Bishop Jones
rbj at rbjones.com
Sat Jan 29 08:10:04 EST 2011
I don't know enough to offer more than the odd comment on
this topic, but here are a couple of points
On Friday 28 Jan 2011 21:19, Steve Bayne wrote:
> 1. A photon is massless
Should be something like "has no rest mass".
It always does have mass.
> This is a given of physics. Another given of physics is
> the momentum of a photon can be expressed this way,
> where 'P' is momentum:
>
> 2. P = E/C (where 'C' is the speed of light; and 'E' is
> (rest) energy)
E is not "rest" energy since that would be the same as rest
mass (units apart).
This simplification of the relationship only applies in the
case that the rest mass is zero.
> Now we, also, have it as a given that
>
> 3. E = MC^2 (Yippee!) And so, from (2) and (3) we get
>
> 4. P = MC^2/C
>
> Leaving us with
>
> 5. P = MC
>
> But wait! Doesn't (5) contradict (1), since 'M' means
> 'mass'?
No because the mass involved is not rest mass.
> 6. P = MV (for picky people assume we are dealing with
> vector properties where applicable).
This is a non relativistic equation, and therefore is not
correct if M is the rest mass.
I think it is still correct if M is the total mass.
> That is: does 'M' in both (5) and (6) get indicated by
> the same units of measure?
Yes I think so. But you must bear in mind that 5 only
applies to objects with zero rest mass, and I think such
objects are always moving at the speed of light, so when the
two equations are both applicable, they both say the same
thing.
Roger Jones
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