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Re: Bernoulli Principle, 2nd try

Wlfgang and Tucker wrote in part:FROM A MOLECULAR
POINT OF VIEW, WHY DOES FLUID PRESSURE VARY WITH
FLUID SPEED?

Here's a stab, but maybe not at molecular level.
Pressure is energy per unit volume. If you think of
the masses and springs model for substances (S,L, or G
states), then increased static pressure results in the
storage of energy in the "springs" (which for liquids
have VERY high, but not infinite, values of k). Now
imagine that compressed fluid moving in a pipe with no
external force doing any work on it. When a
constriction is encountered, the local velocity must
rise b/c of cons of matter. Cons of energy then
requires that the local static pressure (again, energy
per unit volume) must fall, meaning that the springs
relax a bit.

Not exactly molecular, but reasonable based on two
fundamental cons principles. Any help? John Barrere

--- Tucker Hiatt <thiatt@USFCA.EDU> wrote:
At 3:57 PM -0400 6/25/03, Wolfgang Rueckner wrote:
My question is this -- can one make an argument
about what the
pressure difference ought to be from a molecular
motion point of
view? And I'm not talking about a detailed kinetic
theory of gases
derivation but rather a plausible argument that
could be used in an
introductory physics course.

I appreciate your question very much, Wolfgang. I
am disappointed
that the answer seems, so far, to be "No; no one (on
PHYS-L) *can*
explain Bernoulli's Principle from a molecular point
of view."

I certainly wish I could do it. Many of my
introductory students
enjoy learning about the Bernoulli effect, and then
are disappointed
when I am unable to explain it. I am able to take a
molecular point
of view in explaining other fluid phenomena (e.g.,
static pressure,
buoyancy, capillarity, and Pascal's Principle), but
not Bernoulli's
Principle.

So, forgive me PHYS-Lers, but I must re-issue
Wolfgang's question:


- Tucker


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