Re: [Phys-l] Teaching Special Relativity

["Richard Tarara" <rbtarara@sprynet.com>]

----- Original Message ----- 
From: "John Mallinckrodt" <ajm@csupomona.edu>

> > This is what the intro student (indeed myself) comes to special 
> > relativity with.  The magnetic field example (again I must say that  I've 
> > calculated and set the fields for
> > bending high speed protons using 'relativistic mass' and been quite 
> > successful in getting the beam to the target) presents us with a 
> > measured velocity but a momentum that has increased non-linearly  with 
> > that velocity.
>
> Of course.  That's what momentum does.  And I'll bet that I can set  the 
> fields pretty accurately too using the simple fact that the  required 
> field is directly proportional to the momentum.

OK--then help me out here, for my gen-ed students and in fact myself.  Low 
velocity momentum is mass x velocity.  We know the velocity of a an object 
is limited by 'c'.  The momentum of a fast object increases faster than the 
velocity.  Is there really any 'conceptual' way to view this other than that 
the mass has effectively increased.  Saying just that the momentum increases 
non-linearly may be the most 'correct' thing to say, but not very 
satisfying.  I know JD will say use time-space diagrams and maybe that is 
best for science, especially physics students, but I don't have the time and 
I doubt the ability of my gen-ed students to go this route.

BTW:  I once upon a time used Eugene Hecht's gen-ed text "Physics in 
Perspective" where he clearly talks about mass being velocity dependent but 
in his Calculus level text he does not take that same approach.  That, IMO, 
is probably a wise approach overall.

Rick