Re: [Phys-l] question about Bernoulli

[brian whatcott <betwys1@sbcglobal.net>]

On 11/19/2010 12:52 PM, John Mallinckrodt wrote:
> Following up on my earlier post, I think the proper conclusion is that:
>
> 1. In the case of a gas, the pressure drop within a constriction is partially due to decreased molecular speeds, but mostly due to "less squeezing" (i.e., lower density)
>
> 2. In the case of a liquid, the pressure drop is almost entirely due to "less squeezing."
>
> In any event it is not, I think, due to some sort of displacement of the locus of speeds in the translational direction as Brian suggested and as I found at least a little compelling at first.
>
> John Mallinckrodt
> Cal Poly Pomona

Hmmm..I was hoping you wouldn't talk about reduced density: the word 
"Incompressible" is often specified in this Bernoulli connection, after all.
I like to think that kids used to blow  a breath over a strip of light 
tissue.
The key idea is to consider the difference between the total pressure 
along a stream line, and
the total pressure across streamlines - where dynamic pressure is not 
available?
Dynamics does not allow us the luxury of supposing as we often can in 
statics, that
" pressure is the same everywhere."

Brian W