Re: [Phys-l] momentum first and relativistic mass

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

I would counter with this--there are two levels of understanding here. 
Maybe they can be compressed to one--certainly for some it can--but I have 
my doubts for others.  The first level is to understand that there are 
phenomena that cannot be accounted for in the Newtonian models.  Things like 
the momentum of high speed particles, the lifetimes of high speed muons, the 
fact that synchronized clocks will fall out of synchronization with motion, 
etc.  In most texts, and to my mind, that is the 'moving clocks run slow, 
moving masses increase, moving lengths contract' approach to relativity. 
Strange stuff, but these are are instinctive responses to the effects of 
special relativity.  The other level of understanding is the level that you, 
JD, and others would support as the only level necessary--in your words the 
'invariants' approach.  I've read all of John's stuff on this and can't see 
using it with my liberal arts class.  I guess what I am saying is that I 
can't see a group that can't work with simple fractions (the Carnot 
efficiency equation is a great mystery), who often pick up the calculator to 
multiply by one, who ALWAYS pick it up to divide by 10, who can't fathom a 
1/r^2 dependency, (and many other mathematical deficiencies--for most but 
not all) ever really 'understanding' special relativity.  Understanding is 
not the goal--accepting that there are reproducible phenomena that require 
this newer model is the goal.  I would push for understanding at the 'modern 
physics' level of coursework--physics majors, maybe science/engineering 
majors.  I'm not sure everyone here understands how difficult it is to get 
intro students to understand Newton's Laws--how difficult the Force Concept 
Inventory is for most students.  Understanding Special Relativity is a 
difficult goal.  Some might offer then that one shouldn't even attempt such 
at the gen-ed level, but I would counter that the real goal here is to show 
why physics has moved beyond the Newtonian model (with which they can gain 
reasonable, but seldom complete, understanding).

Rick

Richard W. Tarara
Professor of Physics
Department of Chemistry & Physics
Saint Mary's College
Notre Dame, IN 46556



----- Original Message ----- 
From: "Alfredo Louro" <louro.alfredo@gmail.com>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Wednesday, February 27, 2008 6:43 PM
Subject: Re: [Phys-l] momentum first and relativistic mass


> I understand that, but I think I would differ with the idea that
> things like a variable mass makes it easier to understand relativity.
> It seems kind of magical to me, and thus contrary to the spirit of
> relativity, and indeed of physics. I feel the idea that nature only
> deals in invariants is very basic, and I don't like to mess with it.
> But maybe that's my own personal bias. Cheers,