Re: Apparent Weight

[Mark Sylvester <msylvest@spin.it>]

> Date: Sun, 22 Feb 1998 21:11:44 -0600 (CST)
> From: "A. R. Marlow" <marlow@loyno.edu>
> To: phys-l@atlantis.uwf.edu
> Subject: Re: Apparent Weight
> Message-ID: <Pine.A41.3.96.980222201536.124260D-100000@nadal.loyno.edu>
>
> On Sun, 22 Feb 1998, Mark Sylvester wrote:
>
> > Another question:
> > This business of fictitious forces having no 3rd Law counterpart keeps
> > cropping up. Of course, in my seat in the accelerating 747 I feel myself
> > being pressed back into the seat, and the seat pressing back on me, 
>
> I find this descripton very difficult when I try to relate it to my own
> experiences on planes:  what I experience in that situation is the
> pressure of the seat against my back, and I can only believe this is
> pushing *forward* on me --  I don't see how the seat I feel pushing 
> against *my* back can be pushing me in the direction of the back of the
> plane.  Am I misinterpreting "I feel myself being pressed back into the
> seat"??  It is exactly that "fiction" that something is "pressing me back
> into the seat" that has no third law counterpart.  The third law
> counterpart of the push I experience from the seat is the force the seat
> "experiences" from me, and that, of course, is toward the back of the
> plane, but I in no way feel what the seat "feels."

Remember that what I'm after is an effective bridge from the concepts of
Newtonian mechanics to the newer language of GR. To start with, we have to
revise our view about "mg", which has all along been regarded as a force,
like any other force. You sit on a chair, mg pulls you down and R pushes you
up: equilibrium. In the 747, I want to have a backward force which I can
compare with mg and say "You see, mg is just like this force" and then point
out that since we don't need this force if we look at the 747 from an
inertial frame, so we don't need mg either. If the students had never heard
of "the force of gravity" then I probably would not want to do all this, but
they have.

What I do want to avoid is introducing new misconceptions. I guess the
question "Is mg a misconception" is the origin of the Apparent Weight thread. 

Mark

Mark Sylvester
United World College of the Adriatic
34013 Duino TS
Italy.
msylvest@spin.it
tel: +39 49 3739 255