Re: Forces w/o third-law partners???????

[Bob Sciamanda <trebor@VELOCITY.NET>]

----- Original Message -----
From: Leigh Palmer <palmer@SFU.CA>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, October 21, 1999 1:46 AM
Subject: Re: Forces w/o third-law partners???????


> > This is why centrifugal and other inertial forces are called
> > "fictitious" in traditional Newtonian mechanics.
>
> I think that thought is incomplete, Bob. Could you expand
> on it a bit? I've never seen a good reason for the term

If I try to play a game of billiards on a carousel, I will encounter
fictitious centrifugal and coriolis forces.  "Fictitious" because there is
no agent for these forces, momentum is not conserved, etc.  Eg., if I
carefully set a cue ball down on the table (even an "air table") it
mysteriously acquires "un-caused" horizontal momentum.

> . . .(Tell that to the guys who ride in NASA's centrifuge.)

I'm sure I would not have to.  There training was most probably very
Newtonian.  They understand the internal stresses can which occur in an
accelerating body.

> There is no need to continue this traditional practice; it
> does not make mechanical calculations easier. Mysticism
> should be eliminated from physics whenever the opportunity
> is presented, and the principle of equivalence affords us
> that opportunity. There is no difference between inertial
> forces and gravitational forces, just as there is no
> difference between inertial mass and gravitational mass.
> . . .
> Leigh

Quite the contrary.  The student is very mystified when trying to force
these inertial forces into the Newtonian force concept (as, eg., explored
in the FCI approaches).  Newtonian mechanics is very powerful, both for
conceptualization and for doing real-life problems.  In mechanics courses
I stick with Newton, Euler, et.al., emphasizing the utility of this model
in the modern world of physics/engineering, while giving due notice to
later models (QM, SR, GR) which propose other conceptual viewpoints and
which are required for certain experimental circumstances.

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

Long Live Isaac!