Re: [Phys-l] three central misconceptions about relativity

[John Denker <jsd@av8n.com>]

On 10/13/2011 01:53 PM, Philip Keller wrote:
> The question that this makes me ask is this:  Is there a place for
> relativity in high school/AP/1st year college physics, taught this
> way and not the historical way?  I should preface this by saying that
> I am not qualified to teach relativity in the manner that JD is
> advocating.  Like many high school teachers, I learned the physics I
> teach mostly from textbooks --someone has to read them! As you know,
> Halliday and Resnick, Serway, Sears Zemansky @ Young all introduce
> relativity the historical way.
>
> I think that when we teach it that way, it's because true or not, we
> like the narrative.  And we like the dali-esque idea of shrinking
> rulers and slow clocks.  It's a fun story to tell.  But it is also
> true that we don't think that any of our students are going to
> actually use this stuff.  Few enough will go on to design bridges,
> computers and the like.  And look where it is in the book:  at the
> end.  It's late in the year, let's have some fun.  But none of that
> is a good enough reason if in fact it is wrong and if it will have to
> be unlearned later.
>
> So what should a 1st year course say about relativity in the week or
> so available?    Maybe nothing -- use the time for other things?

That's an excellent question.  As they say:  
  It's better to light a candle than to curse the damn darkness.
                       http://vrya.net/bdb/clip.php?clip=136

In that spirit, I've been working on this:
  http://www.av8n.com/physics/spacetime-welcome.htm

It's not finished, and even after it's finished I will need to
rewrite it a couple more times ... but I reckon it's already
better than nothing.  At least it's not wrong.  There's nothing
in there that will have to be unlearned.  In a week you can get
pretty far into the subject at this level of detail.

You can see where it's going:  Lots of spacetime diagrams, lots
of four-vectors, a few hyperbolic trig functions, and lots of
applications to real-world stuff like GPS and kinetic energy.

It makes the point that relativity is not paradoxical.  It's not
even weird.  It's not even particularly esoteric, insofar as it
makes many predictions about stuff that is already understood, 
such as momentum and energy.

It fits into the curriculum because four-dimensional dot products
build upon /and reinforce/ what is already known about three-
dimensional dot products.  Hyperbolic trig functions build upon
/and reinforce/ what is already known about circular trig functions.