Re: [Phys-L] blue road physics

[John Denker <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 ... ?

The full title of the article is "Blue Road Approach to Special
Relativity".  My main response, however, applies to all of teaching,
not just to special relativity.

The "blue roads" in the title refers to the truism that there are
many, many ways of approaching special relativity ... or any other
topic.  The problem with truisms, however true, is that they are
not very informative.

Given multiple possible approaches, we should choose the one that
best serves the long-term interests of the student.  This choice
requires judgment and skill.  Folksy metaphors about shorter or
quicker roads do not even begin to engage the real issues.  It is 
unwise and selfish to teach ideas that seem quick and easy in the 
short term, but have to be unlearned in the longer term.

This is one of the reasons why the art of teaching is vastly harder
than non-teachers will ever understand.  Somebody who understands
physics well enough to ace a high-school physics course is grossly
underqualified to teach the course.  To choose among the N possible 
approaches to any given subtopic, it is important to know how the
ideas will be used years later, used as the foundation for further 
learning, and used in real-life situations.

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

As a secondary point, restricted to special relativity:  The
modern approach is *not* more complicated than the pre-modern
(pre-1908) approach.  The geometry and trigonometry of spacetime 
are *not* more complicated than rulers that can't be trusted,
clocks that can't be trusted, multiple inconsistent notions of 
velocity-dependent mass, et cetera.
  http://www.av8n.com/physics/spacetime-welcome.htm

If the teacher does not understand the modern approach, that's
a problem ... but skirting this problem by teaching the archaic 
approach is not an acceptable option.  Two wrongs do not make
a right.
 1) The students still don't know what they need to know.
  They just incurred a lot of opportunity cost, including
  wasted time and wasted opportunities to appreciate the 
  unity and grandeur of physics.
 2) They are saddled with a load of complicated ideas that 
  will have to be unlearned, at additional cost.

So Huggins is wrong twice over:  Velocity-dependent mass is not
the quick-and-easy approach even in the short term, and even if 
it were, it would be unwise based on longer-term considerations.