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What Einstein Hath Writ.



At 23:46 2/22/00 +0100, Mark wrote:
I was going to put a question to the list on this topic, so I'm following
the discussion with some interest. The question of what to do about rest
mass/relativistic mass vs just mass came up at an IB workshop recently when
we were discussing terminology to be recommended in the new program under
development. Given that I have yet to see an introductory text that uses
the new terms, I find it hard to decide what to do.

At the workshop in question a colleague maintained that the rest
mass/relativistic mass terminology had been shown to be wrong, leading to a
spurious factor of 2 in certain derivations, so that the question was not
merely one of semantics. Promised e-mailing of references has not occurred.
Does anyone know what he was on about?
...
Mark Sylvester

Here is an exposition intended to be exact, aimed at a non mathematical
readership (ref)

"A body moving with velocity v which absorbs an amount of energy E0 in the
form of radiation without suffering an increase in velocity in the process,
has as a consequence, its energy increased by an amount

E0/sqrt[1 - v^2/c^2]

Footnote: E0 is the energy taken up as judged from a co ordinate system
moving with the body.


...the required energy of the body comes out to be

(m + E0/c^2)c^2/sqrt[1 - v^2/c^2]

Thus the body has the same energy as a body of mass (m + E0/c^2)
moving with a velocity v. Hence we can say: if a body takes up
an amount of energy E0, then its inertial mass increases by an amount
E0/c^2; the inertial mass of a body is not a constant, but varies
according to the change in the energy of the body.

...Writing the expression for the energy in the form

(mc^2 + E0)/ sqrt[1 - v^2/c^2]

we see that the term mc^2 which has hitherto attracted our attention
is nothing else than the energy possessed by the body before it
absorbed the energy E0.
Footnote: as judged from a co ordinate system moving with the body.


A direct comparison of this relation with experiment is not possible
at the present time (1920)"

Translators note: With the advent of nuclear transformation processes, ...
the equivalence of mass and energy expressed by the relation E = mc^2
has been amply confirmed.

Ref:Relativity, The Special & General Theory: A popular exposition

A Einstein Trans. R.W. Lawson 1916 15th Ed 1952 with A.E's Preface

-----------------------------------------------------------------------
Brian W




brian whatcott <inet@intellisys.net>
Altus OK