but does the *earth* push up on the *wing*?

[William Beaty <billb@ESKIMO.COM>]

Here's an (edited) repeat of an earlier message which might have been lost
in the increasing traffic... I think it shows where John has made a very
major error, and it needs to be adressed and not just dismissed out of
hand.


On Wed, 18 Aug 1999, John Denker wrote:

> At 02:02 AM 8/18/99 -0700, William Beaty wrote:
> > On Sat, 14 Aug 1999, John Denker wrote:
> /jsd/ So does *everything*.
> /jsd/ Gravity is a force between the earth and the aircraft;
> /jsd/ the only way to counteract it is a force (indirect or otherwise)
> /jsd/ between earth and aircraft.
> /jsd/ The only question is how indirect it is going to be.
> > Everything flys by pushing against the earth?  I strongly disagree.
>
> I stand by my assertion that in a closed system, the wing pushes indirectly
> against the earth.  The only question is how indirect it is going to be.
> My assertion is a simple consequence of Newton's laws.  If we can't agree
> on this, we have nothing further to say to each other.

Perhaps I am confused by the meaning of the word "push".  I take it to
mean "a force."

If you assert that the wing pushes indirectly upon the earth, then by
Newton's laws there must be a force-pair between the wing and the earth,
and the earth must push equally upwards upon the wing.  Are you really
saying that there is a force-pair between the wing and the earth?  Let me
be clear... by "force pair" I mean this:

  The wing creates a downwards force upon the earth, and the earth creates
  an *EQUAL* and opposite force directed upwards upon the wing.  If the
  wing pushes down upon the earth with 10,000Nt, then the earth pushes
  upwards upon the wing with 10,000Nt.  These forces can be indirect and
  mediated by the atmosphere.

Do you agree with the above statement?  If so, then a very important
question arises.  How can the distant surface of the earth push upwards
upon that tiny airplane up there?  If the earth pushes upwards on the
wing, there must be a mechanism by which this occurs.  What is it?  If the
answer is "it just happens", then I will suspect that this force is a
mistake on your part and does not really exist.  To be convinced, I need
something that I can understand and perhaps even visualize.

I can accept that the moving air thrown down by the wing will move through
miles of air and eventually push down upon the earth, but how can the
surface of the earth communicate an equal force up through the miles of
air to impinge upon the wing?  And if the earth does NOT push upwards upon
that wing, then what is your explanation of the lifting force?  The
lifting force is a double-ended entity.  If it does not connect between
the wing and the earth, then just what does it connect to?


It's only my opinion, but I see that John either needs to explain the
mechanism by which the earth's surface reaches upwards and applies force
to an aircraft, or he should begin to suspect that there is no force-pair
betweenthe earth and the aircraft at all.  If there is no force-pair
between earth and aircraft, yet the aircraft does not fall, then John's
model of wing-aerodynamics does not explain flight.  Also, if there is no
force-pair between the earth and the aircraft, then this statement is
totally wrong:

> /jsd/ Gravity is a force between the earth and the aircraft;
> /jsd/ the only way to counteract it is a force (indirect or otherwise)
> /jsd/ between earth and aircraft.

It is wrong because there *is* another way to counteract gravity, and it
doesn't create a force-pair between the aircraft and the earth.  That
method involves the physics of reaction-motors.  You throw mass downwards
and are lifted in return.  Mass hits the earth, but the earth DOES NOT
lift you, the earth only decellerates the down-flung mass.  There is one
force between you and the mass you fling downwards, and there is a second
force between that mass and the surface of the earth as it collides.  No
third force between you and the earth is necessary.  WHere airplanese are
concerned, I see no evidence that such a force exists except when the
plane is within a wingspan or so of the ground.

Very simple and very obvious.  It's pre-highschool Newtonian stuff.
Physics people should not even be arguing about it, and I find it
EXTREMELY strange that it is part of a controversy.

What gives?


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