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.
Cheers,
Joe
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