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Re: [Phys-l] special ed/relativity



The basic concepts of Special Relativity are invariance (tying together all the energy and momentum concepts from earlier in the course) and the mass-energy identity. That can be covered in 3 days without the need for DOT products or the like. Length contrraction and time dilation as a consequence of the constancy of the speed of light can be covered on one day, invariance on a second, and mass-energy on a third. I think John's point is not the math but a matter of not squandering the time available with useless concepts. Use the little time available to best advantage by only covering what is actually correct.

Bob at PC

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From: phys-l-bounces@carnot.physics.buffalo.edu on behalf of Richard Tarara
Sent: Thu 2/28/2008 6:24 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] special ed/relativity



I think Denker has basically insulted everyone who is teaching physics
without doing dot products and 4-space relativity. He seems to have no
sense that there are many different goals for College level physics
courses -- sometimes they are ABOUT physics rather than about being able to
DO physics. The students--the vast majority come into these courses (non
science, non engineering students) as Aristotelian thinkers and we work
quite hard to get some of them to move into the 17th Century and become
Newtonian thinkers. That takes almost a whole semester and is only
partially successful (but I personally do OK at it). It would be unfair, in
my mind, to leave it at that when these students will never take any more
science, so there is some introduction of more modern ideas. The one that
can catch their attention pretty well is special relativity. I have 3 days
for this! It is done totally at the conceptual level--OK I write down the
gamma factor to show those who are more Algebraic (there are a few) why
things get 'crazy' near the speed of light, but basically we start with the
postulates, then what kind of phenomena those postulates suggest, and then
the evidence that any of that happens. Once again, the main point here is
to show that the Newtonian model we've been working with is insufficient.
This is about the way science works and progresses--moving from one model to
the next better model etc.

Everyone who teaches this level of student recognizes the problems I
outlined and we will not be intimidated by the insults John is throwing out
here--just the subject line is enough (so I've deleted the rest of the
post). The overall level of students may not be quite as bad as I make it
sound--they actually write pretty well and can use Excel quite nicely--but
algebraic ratios are a 'no-go' and dot products, vectors in general,
calculus in particular, are not in their current toolkits--all conveniently
forgotten since HS (if they ever knew such). I guess John would sweep the
schools clear of such students--might help the taxpayers since it would
empty many a school!

I'd make more pithy statements about John's attitude here, but I'd like to
stay on this list. ;-)

Rick


----- Original Message -----
From: "John Denker" <jsd@av8n.com>

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