Re: lost msg: Re: bad-faith argumentation (was *earth* vs. *wing*)

[William Beaty <billb@ESKIMO.COM>]

On Tue, 24 Aug 1999, Brian McInnes wrote:

> Hi All,
> Comment on John Denker and William Beaty's discussion on direct and
> indirect forces.
> Surely this is not a matter of semantics.  In theNewtonian model that
> I and, I believe, many others use there are two types of force:
> contact forces and
> action-at-a-distance force.

I think it is the second one which is an issue here.  John Denker's
thought-experiment with the baseballs illustrates it wonderfully: a "gauge
field" with baseball-mediated repulsion force.  The baseball sequentially
reflects from a trampoline and from a wooden board suspended horizontally
above it.  As a consequence, the board is accelerated upwards, and the
trampoline (and the earth below it) is accelerated downwards.

I would immediately agree that this is a "force" in the full Newtonian
sense, regardless of the impulsive nature of the particle-exchange.

John Denker says that there's a force between the wings of a high-flying
aircraft and the surface of the earth.

Now if we had baseballs or air molecules bouncing from the earth and
returning to bounce from the wings, then I would agree that there is a
force between earth and plane.  It doesn't even have to be the same air
molecules!  If we had a sort of "Newton's Cradle" effect where sequential
collisions between air molecules mediated the interaction from wings to
earth, and similar sequential collisions mediated the interaction between
earth and wings, then I would agree that there is a force between earth
and plane.  There is no force.  How can I be so certain?  Because there is
an obvious situation where a high-flying object can be lifted by a force
between itself and the earth.

Suppose we have a mile-tall cylinder (of any width), and it is full of air
and placed vertically against the earth's surface.  Next we place a
close-fitting piston into the hollow interior at the top.  That piston
will slide down a bit, but then it will come to rest.  That piston is now
pushing on the air, the air is pushing on the earth, and vice versa.
There is a force between earth and piston.

When an airplane flys high above the earth, is there a force like this
supporting it?  Of course not.  There is no constraining mechanism to
create a "columnar piston" effect.  Specifically, if the airplane should
move downwards, it will drive air outwards, and the "interaction" will
spread downwards like a sort of cone-shape.  ("Interaction", not "force".
The word "force" has a specific meaning which should not be messed
with unless we have very good reason to improve or "repair" our
definition.)

Ok, the plane moves downwards a bit, and it creates a downwards-moving
"cone shape" of interaction.  This will eventually hit the ground, no?
Certainly.  It might even hit the ground undiminished, since we can
integrate the amount of interaction spread over a large surface and maybe
discover that it is the same amount of interaction localized immediately
below the downwards-moving airplane.

But then this cone of interaction reflects from the earth and moves
upwards.  IT CONTINUES TO SPREAD.  It does not somehow narrow itself and
concentrate on a single airplane high in the sky, instead it spreads
immensely outwards.

How can I be so damned certain that this is true?  Easy.  The
"interaction" is identical in nature to a sound wave.  Refer back to our
"columnar cylinder."  When we placed the "piston" at the top, it created a
propagating region of increased pressure which moved downwards and
communicated with the surface of the earth, and also moved back upwards.
In other words, the heavy piston "feels" the presence of the earth through
use of sound waves of approximately zero frequency.  The same effect
occurs when I pull on a rope and then a person at the far end of the rope
feels the interaction.

When an airplane moves suddenly downwards, it launches a feeble
low-frequency sound wave in much the same way that our earlier piston did.
However, since the columnar tube is not there in the case of the airplane,
the sound wave reflects from the earth and continues to spread outwards on
its way back up.  The airplane cannot "feel the earth" in the way that our
piston did.  The high-flying airplane must use some other method in order
to remain aloft.

John Denker, what do you suppose this alternate method might be?  :)



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