Note that Pete does not bother to mention that he uses a different
meaning of the word "mass" than do virtually all modern physicists (and
many posts in this thread). Consequently, he sheds more confusion than
light on the subject -- such PUNs must be acknowledged and understood,
or arguments are just useless.

As one result of this, he needs a page of algebra (in that link) to show
what is inherently included in a better, more basic postulate: the
conservation of 4-momentum. And by using nonstandard terminology he
comes to a different conclusion: his "mass" is conserved, while in the
standard vocabulary we say the same thing using different words: ENERGY
is conserved [#].

When Pete says "mass", he means what the rest of us mean by
"relativistic mass", an anachronistic concept that has some application
to the elementary subjects Pete considers, but is useless in advanced
topics such as General Relativity and relativistic quantum field theory.
This archaism survives in some simple statements, such as "mass
increases with velocity"; to make sense of such statements, one must be
careful to understand the PUN involved and be aware of this old
confusion of nomenclature.

In summary: with Pete's meaning of "mass", "mass" is conserved. Using
the standard meaning of the word, mass is not conserved, but energy is
conserved. In our everyday lives we can behave as if mass were
conserved, because the magnitude of the error involved is vastly too
small to be noticed. But in most current areas of physics research,
Pete's approach is useless. For instance, in studies of collisions at
particle accelerators, Pete's approach is excessively naive,
"relativistic mass" is useless in the underlying theories, and mass most
definitely is not conserved in such interactions (often by several
orders of magnitude).

[#] There are some caveats to this; all of them are satisfied
in the conditions of Pete's derivation in the above link.

Isn't it enough to just say: “ Mass = Energy / c^2 ” ?

Thanks for the link:
“ GeoCities.COM/physics_world/sr/conservation_of_mass.htm ”.
But for someone like Sanny, who knows little English or physics,
isn't it enough to just say: “ Mass = Energy / c^2 ” ?

Am Sun, 31 Aug 2008 13:09:24 -0400 schrieb "Pmb" <[Only registered users see links. ]>
in [Only registered users see links. ]:

Good work there. Since all the steps can be reversed, given equations
2a and 2b, that URL actually shows that conservation of momentum is
equivalent to conservation of mass (providing there is no matter-energy
conversion, as in matter-antimatter annhiliation).

--
// The TimeLord says:
// Pogo 2.0 = We have met the aliens, and they are us!

You wrote:
“ ‘ m = E / c^2 * sqrt( 1 - v^2 / c^2 ) ’
So for fixed energy,
the mass goes to zero as speed approaches the speed of light. ”.

“ Mass** ” goes to infinity as v approaches c:
“ Mass = Energy * c^-2 * ( 1 - v^2 / c^2 )^-.5 ”.
** i.e. “ Relativistic Mass ”,
not “ Invariant Mass ”, not “ Intrinsic Mass ”, not “ Proper Mass ”.

"jmfbahciv" <jmfbahciv@aol> wrote in message...
news:[Only registered users see links. ]...

None of this makes much sense, i'm sorry to say. Are
we forgetting that m = E / c^2 contains "c", not "v", or
IOW the constant "c" is not expected to change? This
formula only shows the amount of change in mass that
results from a given E, energy loss or gain. And in its
more classic form, E = mc^2, it yields the amount of
energy that results from a given loss of mass. "m" in
this formula is actually a delta m, a *change* of mass.

And yes, it *can* be shown using other forms that
mass will indeed tend toward infinity as v tends
toward c.

While speed and velocity are interchangeable among
non-physicists, they are different within the realm of
science. Speed is scalar, and velocity is vectorial.
That just means that speed has one value only, the
rate of motion, while velocity is the speed plus the
*direction* of motion.

The speed of electromagnetic radiation, "c", is not a
vectorial quantity in E = mc^2. It is scalar.

Yes, i know this could probably be argued until all our
hairs fall off. So do so if you like. "c" is a scalar speed,
not a vectorial velocity.

You wrote:
“ "m" in [ e = m * c^2 ] is actually a delta m, a *change* of mass. ”.

No, “ Mass = Energy ”**.
** using “ natural units ”, where “ c = 1 ”.
By “ Mass ” Einstein meant “ Relativistic Mass ” ..
not “ Invariant Mass ”, not “ Intrinsic Mass ”, not “ Proper Mass ”.

Am Wed, 03 Sep 2008 11:58:38 +0000 schrieb Jeff▲Relf
<Jeff_Relf@Seattle.Invalid> in Jeff_Relf@Seattle.2008_Sep.3|4.58am|j
in sci.physics.relativity:

Actually I wrote:

*** begin ***
m = E / c^2 * sqrt(1-v^2/c^2)

So for fixed energy, the mass goes to zero as speed approaches the speed
of light. [smile] (Just kidding on that last statement.)
*** end ***

Look at message <[Only registered users see links. ]> and
read it again. I didn't mean for the statement to be true, just a
joke for the benefit of those that reach similar stupid conclusions
as that statement. The odd thing is that the statement is true, just
baseless, since the energy can not be fixed as v changes. Change the
v and you change E. So assuming that you have the same E for all v is
ridiculous.

Relativistic mass is obsolete. We no longer teach it.

--
// The TimeLord says:
// Pogo 2.0 = We have met the aliens, and they are us!