Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] Relativisitic mass vs Invariant mass



Laurent Hodges wrote:
I remember reading something by Einstein once (a paper? a chapter in a book?)
and noting he didn't write E = m c^2 but E-sub-0 = m c^2, where m was clearly
what we call the rest mass.

Well, that paper/book must have been a fairy tale.

Take a look at the original article:
Einstein (1905d)
"Ist die Trägheit eines Körpers von seinem Energiegehalt abhängig?"
http://www.zbp.univie.ac.at/einstein/einstein4.pdf
or the English translation:
"Does the Inertia of a Body Depend Upon Its Energy Content?"
http://www.fourmilab.ch/etexts/einstein/E_mc2/e_mc2.pdf

Uncle Al does not write (m_0) or even (m). In the crucial sentence, he
writes out the word for mass.
Gibt en Körper die Energie L in Form von Strahlung ab,
so verkleinert sich seine Masse um L/V^2.

... where L denotes energy and V denotes velocity.

So it seems pretty much undeniable that -- in 1905 -- he was
suggesting that a particle would change "its mass" as a function
of its energy.

Later, after the geometric view of special relativity came along,
Einstein did adopt it ... and he relied on it during the development
of general relativity.

The Oas article mentions Einstein's mature view on page 1.

=================

As I have mentioned many times before, history is usually not
a good guide to pedagogy.
a) Just because Einstein did it the hard way in 1905 doesn't
mean we have to make our students do it the hard way now.
b) It is common to find teachers who so firmly believe in
following the historical approach that they just make up
a false history and follow that! IMHO there is no excuse
for this. Two wrongs don't make a right; in this case (b)
we have a wrong pedagogical theory coupled with false
historical "facts".

Good pedagogy should be logical and straightforward; history
is not. The true history involves much backtracking out of
blind alleys and dead ends. Kuhn had something to say about
this.

Teaching, especially at the introductory levels, should start
with the best available evidence ... which rarely coincide with
the most ancient available evidence. Ditto for best concepts
versus ancient concepts.

===============================================

Thanks, Joel, for pointing out the Oas article!
http://arxiv.org/PS_cache/physics/pdf/0504/0504110.pdf