Re: [Phys-l] question about Bernoulli

[John Denker <jsd@av8n.com>]

On 11/23/2010 02:52 PM, John Mallinckrodt wrote:

> I would again suggest (as I did a few days ago in more detail) that,
> for situations observing a generalized Bernoulli's law (which applies
> to steady, nonviscous, *compressible*, streamline fluid flow and
> encompasses so-called "incompressible" flow):

> 1. In the frame of the fluid, the molecular velocity distribution is
> isotropic.  Any anisotropy is a simple and direct result of working
> (as one must) in *the* frame (for non"boring" cases†) in which the
> flow is "steady."

Any anisotropy?  Even if the velocity distribution is isotropic,
the acceleration is likely to be anisotropic.  The laws of physics
include acceleration terms.
 
> 2. The pressure reduction in high velocity areas is mostly a direct
> result of lower density (less "squeezing") and only partially a
> result of smaller average velocities (due to the temperature
> reduction that accompanies the barotropic density reduction)

Direct result?  You can't have one without the other, so there
is no logical basis for deciding which is the "cause" and which
is the "result".  Maybe you can decide on metaphysical grounds,
in which case I'm not interested.
  http://www.av8n.com/physics/causation.htm

> 3. The role of velocity/temperature changes becomes negligible as one
> goes to the "incompressible" limit.  In that limit, the (close to
> negligible) density reduction is almost entirely responsible for the
> pressure reduction.

Again, assigning "responsibility" for a "result" has no basis
in physics.  The velocity increase and the pressure decrease
and the density decrease go hand-in-hand and that's all the
laws of physics say about it ... and that's all that needs to
be said about it.