Re: [Phys-L] blue road physics

[Isaac Bickerstaff <jsd@av8n.com>]

On 11/09/2012 11:11 AM, Bill Nettles wrote:
> Is anyone composing a response to Elisha Huggins's article on
> relativistic mass and mass of a photon in November 2012 ,The Physics
> Teacher?  First he ignores C. G. Adler's paper (Am. J. Phys., 55(8),
> August 1987) which addresses the problems associated with
> "relativistic mass." Next, he asserts that using relativistic mass is
> just another correct way to do the physics. Finally, he uses special
> relativity in an accelerating reference frame to talk about
> trajectories of photons.  He never approaches relativistic momentum
> as _gamma_mass_velocity.
>
> He wants to introduce SR early, an admirable thing.  Why would he
> use, at best, an out-dated concept (see Adler cf. Feynmann Lectures
> of 1963), and at worst, a mistaken concept ( versus GR)? Adler points
> out that even Einstein discouraged the velocity-dependent mass.
>
> It seems to me that his approach is similar to saying the Bohr model
> is right simply because it gives the right energy answers.
>
> What think ye?

Huggins asks a crucial rhetorical question:

> Weightlessness does simplify the physics, but now you
> have to prepare the lab on Newton’s second law F = ma. How
> do you measure or define m? 

Huggins immediately slays several straw men:

> You cannot weigh an object be-
> cause it does not weigh. We leave it to the reader how she or
> he would design the lab to illustrate F = ma. You have the usu-
> al stuff like metersticks, stopwatches, string, pulleys, springs,
> etc. There is even an equal arm balance, but you cannot figure
> out what its use is.

He then answers the rhetorical question by use of the equation p = m v, 
where v is dx/dt i.e. the reduced velocity aka the classical coordinate 
velocity.

He cleverly leaves unmentioned the equation p = m u, where u is dx/dτ
i.e. the 4-velocity in spacetime.  Similarly he leaves unmentioned other
operational ways of measuring mass, such as a centrifuge moving with a 
specified classical velocity, which would have given one or two additional
/inconsistent/ values for the relativistic mass.
  http://www.av8n.com/physics/spacetime-acceleration.htm#sec-discuss
Leaving out conflicting data is a valuable technique for winning an argument.
Facts would just confuse me, and would confuse the poor innocent students.
We have seen this in the recent political debates.  People who blather about 
"integrity" are idiots who do not appreciate the importance of winning the 
argument:
  http://calteches.library.caltech.edu/3043/1/CargoCult.pdf

This relativity article is part of a series that includes the recent 
contribution by H.S. Leff (five parts, ~16 pages) that explains entropy
in terms of spatial energy-spreading.  The same powerful pedagogical 
techniques are used, namely leaving unmentioned the many obvious counter-
examples, such as a gas at a not-too-high temperature in a tall thermally-
insulated cylinder in a gravitational field.

These contributions are valuable for teaching students that everything
we have learned about relativity since 1908 is wrong, and everything we
have learned about thermodynamics since 1898 is wrong.

I myself have contributed a couple of articles to this series:

  I. Bickerstaff
  "Phlogiston for Everyone"
  The Physics Teacher (2012)

  I. Bickerstaff
  "Practical Applications of N-Rays"
  The Physics Teacher (2012)

All in all, this series will serve as a lasting monument to the wisdom
of the reviewers and editors of The Physics Teacher.