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

[William Beaty <billb@ESKIMO.COM>]

On Fri, 20 Aug 1999, John Denker wrote:

> I apologize for making an error.  I'm not sure it was a "major" error.

Um... are we talking about the same error here?  I'm talking about a clear
violation of Newton's 3rd law, not about word games.  And this issue
obviously has some bearing on your critique of the Anderson/Eberhardt
paper, so for this reason I cannot just let it go unanswered.

> My error was that in one message out of a hundred, I failed to play defense
> sufficiently carefully.  I wrote words which were open to
> misinterpretation, especially when taken out of context.

I don't understand.  What error do you think I'm referring to?  Is this
the problem here:?

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

I agree that the above is a minor error.  I see that I should not have
mentioned it at all because it is a distraction from the main body of my
message (see original below).  Please ignore it, it's done with, very
sorry I said anything.

If you read the original message again, you'll notice this part:

> 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 between the earth and the aircraft at all.  If there is no
> force-pair between the earth and the aircraft, yet the aircraft does not
> fall, then John's model of wing-aerodynamics does not explain flight.


As I understand it, we have long been arguing over whether the lifting
force arises because of a force between the wings and the earth, or
because of a force arising from the wing's reaction against the mass of
local air only.  In other words, is the lifting force caused by
"Circulation/earth-surface," or is it caused by "Newton/Downwash?"  Does
the aircraft push down upon the earth and as a consequence the earth lifts
it up, or does the aircraft accelerate air downwards and is lifted
upwards as a consequence?

If you agree that there is no force between a high-flying airplane and the
surface of the earth, then I think this means that you have changed your
earlier stance regarding the origin of lift.

Do you still assert that the circulation creates upwash, and that this
upwash then drives the wing upwards?  That's what you seem to say in
http://www.monmouth.com/~jsd/fly/lift.htm   Has your position on this
issue changed significantly?

> I failed to defend against those who would rather play nit-picky word games
> than seek an understanding of the physics.

I'm seriously trying to understand the physics, and if your reasoning
about the lifting force is based on a violation of Newton's laws, then we
really need to discuss this.  If you are wrong, then I need to be certain
that you are wrong, because otherwise I cannot be certain that the error
does not lie with me instead.

Suppose I am wrong about all these issues.  If there is no violation of
Newton's laws in your explanation of flight, then I must consider it
extremely important that I be shown the error of my ways.  I'm always
willing to take my lumps in my quest for understanding.

If John doesn't have the time to show me my error, then perhaps somebody
else here will help me out.  How can wings of a high-flying plane produce
a force between the earth and the wings?  I think I understand how a
balloon can do this, but I fail to understand how a wing does it.  Or
alternatively, how can circulation cause an airplane to remain aloft,
unless that circulation reacts against some mass of air and throws that
mass downwards?  If it does not throw net mass downwards, and if there
also is no force between the airplane and the earth's surface, then
Newton's laws are violated.  If they are NOT violated, then I require an
explanation so I can understand how flight really works.

Also, in the previous message I ask a number of questions (below).  If
these go unanswered, then I can no longer be certain about John's position
regarding the origin of the lifting force.  If he has changed his position
significantly because of recent messages on phys-L, then I have no way of
knowing this, or of knowing what his position now is at present.


> This is my second apology.  Demands for further apologies will go
> unanswered.

I'm sorry, I must have missed your earlier apology.  I certainly don't
recall you admitting that you had made any serious mistakes in physics.
If an explanation of the aerodynamic lifting force contains a violation of
Newton's 3rd law, then that certainly is a serious mistake in my book.
If Newton's laws are now becoming "word games" and "nit-picking", then
I fear that this thread really no longer has anything to do with science.

On a (lighter?) note, I've always believed that there's nothing wrong with
making terrible mistakes in public as long as we admit to them quickly and
do not try to hide them.  Admitting to embarassing blunders is a sign of
good character.  And when we learn to understand physics, trial and error
REQUIRES lots and lots of error.  Hiding errors and hoping nobody will
notice is extremely counterproductive, and I absolutely refuse to play
that game.  Hiding errors is certainly not a part of the blatantly-honest
"Scientific Integrity" that I attempt to follow.  I would rather display
my shameful errors for all to see.  It totally defuses them as an
emotional issue.




 ========================================================================
Date: Fri, 20 Aug 1999 18:06:58 -0700 (PDT)
From: William Beaty <billb@eskimo.com>
To: list physics teaching <phys-l@lists.nau.edu>
Subject: but does the *earth* push up on the *wing*?


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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