Re: What is weight? (was Re: Internal or external?)

[Leigh Palmer <palmer@SFU.CA>]

> I would phrase it that astronauts *feel* weightless, because the
> sensation of "weight" is really the reaction force of the floor against
> our bodies. It is this reaction force that is now missing since both the
> person and the "floor" are now in free fall. Thus the person *feels*
> weightless, but still has the same weight (suitably reduced due to
> increase of R).

The feel of weightlessness (and, consequently, weight) is more
than the reaction force exerted by the floor. As I pointed out,
it's not the same as floating neutrally bouyant. If you don't
understand that, next time you go to the swimming pool, jump
feet first off the ten meter tower. You'll feel your testicles
as weightless - dramatically! It is quite a deterrent to going
off feet first; I much prefer to go head first.

Many of my students fly experiments on the "vomit comet"
(Canada is committed to pay for more flights than it can fill).
I am told that half of them get sick. Fortunately this does not
happen in our swimming pool at SFU when people float.

> I think it is near impossible to make a sensible and consistent
> definition of weight other than the gravitational attraction of the
> Earth.

If that is the case then I claim you haven't listened to what
I've been saying.

> But one cannot feel a gravitational force (a central and
> surprising point to most students). If (uniform) gravitation is the only
> force acting, we feel nothing because we are in free fall. We feel only
> other forces, we cannot sense a gravitational force which is uniform
> over our bodies.
>
> Jerry Epstein

I know what you're saying here, Jerry, and perhaps it ought to
be true, but I'm not intending to insult you when I tell you
to go take a flying leap. We are so used to having weight that
weightlessness feels very different. It is, perhaps, ascribable
to a series of reaction forces within our bodies, successively
pushing up on organs which have, in turn, their own weights. I
rather think that our inner ears are adapted to weightfulness
in all orientations, and the sensation of weightlessness is
simply something to which our central nervous systems have not
become accustomed.

Leigh