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Re: General Theory of Relativity



On Fri, 11 Dec 1998, kevin sonntag wrote:

I have a question if anyone has ideas on how to present to introductory
level students , the concept of when two objects are approaching each
other close to the speed of light that their combined speed between them
cannot be greater than the speed of light. I have tried to relay the
concept to my students, but I am not reaching them.
Any help would be great

Kevin Sonntag
KHS

I think you may be underestimating your success in reaching students on
this point. Due to successful high school teaching, I find that most of
our freshmen arrive with a fairly good feeling for the oddities of special
relativity, or at minimum with an openness to accepting them.

As for presenting Einstein's special relativistic velocity addition, I
don't see any way short of giving your students the actual formula

v12 = (v1 + v2)/(1 + v1v2/c^2),

even without any derivation, stating it as a consequence of Einstein's
1905 corrections of Newtonian physics following from a correct
understanding of c as an invariant ultimate speed for all observers. You
can point out that the correction term v1v2/c^2 is extremely small for
ordinary life speeds v1 and v2, and was unsuspected in Newton's time, but
it is just sufficient to prevent speeds less than or equal to c from ever
adding up to anything greater than c.



A. R. Marlow E-MAIL: marlow@loyno.edu
Department of Physics, Box 124 PHONE: (504) 865 3647 (Office)
Loyola University 865 2245 (Home)
New Orleans, LA 70118 FAX: (504) 865 2453