XPost: sci.physics.relativity
From: PointedEars@web.de

Paul.B.Andersen wrote:
> Note that m = 3.089167695E-28 kg is the _lost_ mass,
> it doesn't exist any more.
> So where has it gone?
> It is converted to E = mc² ≈ 2.776404839E-11 J of _kinetic energy_.
> Kinetic energy is not mass. Thus "convert".

/Non sequitur./

>>         Second, "E=mc^2" only applies to systems at rest. In general,
>>    it's "E^2=(mc^2)^2+(pc)^2", where "p" is the system's momentum.
>>    (That basically says mass is the magnitude of the four-momentum.)
>
> E = mc² is the energy content, or the energy equivalent of
> the mass m.

The first wording is simply wrong.  E (better: E₀) is the *rest* energy of
_an object_ whose mass is m.  One can also call that the energy content _of
that object_ at relative rest (as Einstein did, but this wording is
obsolete), but NOT "of the mass".  Mass is a quantity, not a object; a
quantity has no content.

> Mass is invariant, so this equation is valid for all speeds of the mass.

Again, mass is a quantity, NOT an object.  It does not make sense to say
"speeds of the mass".  That makes as much sense as e.g. "mass of the charge".

> However, the _total_ energy of a moving mass is:
> E = mγc² = mc² + (γ-1)mc²
> The first term mc² is the invariant energy content of the mass m,

No, the first term is the rest energy equivalent to the mass m.

Mass does not have an energy content, _objects_ have.

> the second term is the kinetic energy of the mass m.

No, it is the kinetic energy of an _object_ with mass m and relative speed
v, hidden in γ = γ(v).

> Kinetic energy is not mass!

And mass is NOT energy or "has energy".  You would be well to realize that.

>>         Third, mass is conserved in nuclear fission. This point is often
>>    explained incorrectly, even in otherwise solid textbooks like Grif-
>>    fiths.
>
> Could it be that you are wrong and the textbook is right? :-D

He is wrong, obviously.  But you are also wrong in multiple respects:

> Before the fission the mass of the U-235 nucleus + 1 neutron
> is: m₁ = 3.919748214E-25 kg
>
> After the fission the mass of the Ba-141 and Kr-92 nuclei + 3 neutrons
> is: m₂ = 3.916659047E-25 kg.
>
> So the mass isn't conserved,

Correct.

> m = m₁-m₂= 3.089167695E-28 kg has disappeared because it is converted to
> kinetic energy which is not mass.

Again: NOT the mass is partially converted to kinetic energy, but the rest
energy E_0 = m c^2 *equivalent to* the mass m.

--
PointedEars

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