Re: Scientific Errors

Dennis B wrote:
There exist many errors and misnterpretations which are perpetuated
within the scientific community which require correction. The first
error I shall correct concerns "Bernoulli's Principle", with which it is
erroneously taught that the pressure of an accelerating fluid decreases
as the velocity of the fluid increases. The indisputable fact is
Newton's laws of motion reveal the exact opposite to be true.

No, they don't.

At a narrowing of the tube, the flux rate is the same as at any other
cross-section of the tube, but the cross-sectional area is smaller,
therefore the flow is faster.

In order for the flow speed to increase, the average speed of the
molecules must increase - they are accelerated into the narrow space.

After the narrow space, they are decelerated.

An accelerating fluid passes from a region of higher pressure to one of
lower pressure. A decelerating fluid passes from a region of lower
pressure to one of higher pressure.

Since the fluid first accelerates before the constriction, then
decelerates after it, the constriction is therefore at a lower pressure
than either of the adjacent, wider sections.

This is enough to prove to you that you did something wrong, but I'll
deal with your explanation point-by-point so you can see what you did
wrong:

The fluid is comprised of particles with mass. Therefore, in accordance
with Newton's equation "F = ma", as the fluid accelerates (relative to a

F = ma applies to a rigid mass and an external force. Trying to apply
it intrnally to a nonrigid mass - even one comprising a collection of
unconnected rigid masses - is fallacious and unscientific.

reference point)...there is a corresponding increase in the force
exerted by the fluid in the direction of motion,

False.

If the force were increasing as we travelled along the tube, the
molecules would be forced backwards and slowed, not forwards and
accelerated.

Since the molecules are accelerating into the constriction, the force
is decreasing.

This acceleration is not due to external forces. It is due to internal
rearrangement of the velocities of individual molecules. Within the
fluid, molecules are colliding and seeing occasional forces from all
directions. The density is constant throughout the system, so the
probability of a collision is constant, though the momenta transferred
by the collisions are not. As the pressure decreases, there is less
probability that a molecule moving in that direction will rebound from
another in front of it with a rearward momentum higher than its prior
forward momentum. The effect is of a higher average impulse behind the
molecule and a lower average impulse in front of it, thus a
more-probable acceleration of molecules in that direction.

In more simple terms, it is possible for a molecule to collide with
molecules before it in such a way as to send it backwards, but the
effects of its collisions from the rear will exceed those to the front
and it will have a net forward acceleration. As it travels along, its
average speed increases, as the pressure around it decreases. Even
though the density does not.

Again, the situation is reversed after the constriction, with the
faster molecules colliding with the slower ones in front, which provide
a back-force and increase the pressure seen from the front.

However, if the tubes are the same size before and after the
constriction, the pressure in the latter tube will be lower than the
pressure in the former, though still higher than in the constriction.
This is why the fluid flows through the constriction at all. Such
constrictions are known as throttles. They should not be confused with
nozzles, which are open to the outside system, and whose job is to
maintain the high speed created by the constriction, so as to eject the
fluid, either to dispense it at high speed, or to shed its forward
momentum with the result that the tube and nozzle are propelled
rearward, which maintains net zero momentum of the universal system.

and a corresponding
decrease in force opposite the direction of motion. The apparent
decrease of pressure in an accelerated fluid is the result of fluid
particles moving away from a surface,

This does not apply at all. The statement of the Bernoulli principle
requires the density to be a constant at all places within the fluid.
If the density is not a constant, you have another problem entirely.

And your tautology about density changes causing pressure changes is
fallacious. Density only causes pressure changes when (a) the density
is changing due to transient motion of regions of fluid and (b) the
density is changing due to phase change (fluids evaporating or
condensing, or chemical reactions that change the number of molecules
in the fluid, though the endo-/exo-thermic effects of chemical changes
are usually more significant).

Normally, it's pressure differentials that cause density changes. But,
as I said, that doesn't apply to your problem.

thus creating a region of negative
pressure relative to the positive pressure exerted by moving particles
impinging upon the opposite side of the surface (such as the underside
of an airplane wing, for example).

I wouldn't trust you to fold a paper airplane, much less design a real
one.

To Be Continued...

Why continue? You've already spent this post expositing on something
you know to be wrong because the data exist to show that it is wrong.
Or you never bothered to look at the data. Which is worse.

At this point, you should question every one of your ideas that attempt
to refute any part of basic science. Learn the truths about the simple
things first. Then, when you've got that all correct, you might know
enough to start challenging the things that science is suggesting but
hasn't proved yet. Until then, you're not a scientist, nor an
explorer, nor a thinker, nor a reformer, nor a messenger, you're just
another nut.

--Blair

.

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