Re: relativistic velocity addition paper

[Hugh Haskell <hhaskell@MINDSPRING.COM>]

At 21:20 -0500 2/4/02, Joe Heafner wrote:
> Last week I discovered the very short paper by Mermin (AmJPhys 51,
> 1130 (1983)). Mermin demonstrates a WONDERFUL derivation of the
> relativistic addition rule using only the first postulate of SR
> (invariance of c). Today I handed out copies of the paper to my
> intro astronomy students and we went over it to basically wrap up
> our study of SR. They enjoyed it and so did I.
>
> Actually, this paper references one by Greenwood (AmJPhys 50, 1156
> (1982)) that derives the same result but presupposed knowledge of
> time dilation and length contraction. I find Mermin's paper better
> suited for introductory astronomy.
I agree. It is an excellent paper, and one of the few Mermin has
written that I can actually understand. I have used it to introduce
relativity in my intro physics course a few times and was pleased
with what the students got from it. It is the only derivation of the
velocity addition law that doesn't use the Lorentz transformation. Of
course, once you get the LT the derivation is easier, but it requires
calculus which makes it forbidden territory for a non-calculus
course, so Mermin's work, which is also quite intuitive is really a
good place to start. All you need is the constant speed of light
postulate and a willingness to work through some tricky algebra, but
at the end the students at least know where this strange correction
term in the addition of velocities comes from.

Hugh
--

Hugh Haskell
<mailto://haskell@ncssm.edu>
<mailto://hhaskell@mindspring.com>

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