Re: Bernoulli's equation

["John S. Denker" <jsd@MONMOUTH.COM>]

Wolfgang Rueckner wrote:
> .... from a molecular point of view

First of all, a warning:  Thinking about fluids from a
molecular point of view is not always a good idea.

In principle (!) you can start from the submicroscopic
molecular properties and work your way up to the
macroscopic fluid properties (such as pressure, density,
airspeed etc.), but for most everyday applications the
fluid description is a better way to visualize what is
going on.  That's because people tend to grossly
underestimate the number of particles in the fluid, and
to grossly underestimate the importance of their
interactions.

http://www.monmouth.com/~jsd/how/htm/airfoils.html#sec-fluid


I will answer Wolfgang's question in terms of a small
parcel of fluid rather than in terms of a molecule.  If
that isn't satisfactory please re-ask the question.

I would work backwards from the velocity:
 -- If there is a change in velocity, there must have
been an acceleration.
 -- If there is an acceleration, there must have been
an unbalanced force.
 -- An unbalanced force comes from a difference in pressure,
i.e. a pressure gradient.  (Pressure per se, a constant
pressure, won't do it.  This point is often overlooked.)

You can work out the remaining details.

> Does the equipartition theorem come into play here?

No.