Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

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,

Alfredo

On Wed, Feb 27, 2008 at 1:19 PM, Rick Tarara <rtarara@saintmarys.edu> wrote:
Let me try and make my point clearer. What I'm suggesting is not denying or
ignoring the 4-space/Minkowski/Denker approach, but rather trying to justify
an introductory approach that deals with slow clocks, compressed lengths,
and increased mass BECAUSE as 3-dimensional beings living in linear time
(unlike the wormhole aliens of DS-9 ;-) our experiences--or at least our
extrapolations to what we think we would experience tend to fit those ideas.
Thus, a first pass through SR with slow clocks etc. seems more reasonable to
me than immediately jumping into a more mathematical approach.

Rick


----- Original Message -----
From: "Alfredo Louro" <louro.alfredo@gmail.com>
>
> Four-momentum is m dr / d tau, where tau is the proper time, and dr is
> a displacement in space time [dt, dx, dy, dz]. Thus the time component
> is gamma m, and each of the spatial components is gamma m v_{x,y,z}.
> The gamma doesn't appear because the mass is variable, but because
> ordinary time is not invariant. You can also define a four-force as
> dp/d tau.
>
> I think a good approach is to think that nature doesn't know about
> different reference frames. So we expect any natural laws that arise
> to refer to invariant quantities. There is an invariant mass.
>
> Another thing worth considering is that while you can recover the
> familiar newtonian mechanics in the limit v << c, you can't really
> extrapolate in the other direction.
>
> Alfredo



_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l