Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: pressure-energy density

I've always looked at this equation (with rhos rather than 'm's--yes you
defined m as a density) as an energy conservation equation. Energy per
unit volume. The last two terms are clear--KE per unit volume and
gravitational KE per unit volume--but what about P. Well rewrite P as
(F*d)/(A*d) where d is some imagined distance through which the fluid is
pushed (doesn't have to be compressed) and A is an area. Now you have the
work per unit volume. Anyway, that's the way I learned it--Work/volume +
KE/volume + grav PE/vol = constant.

Rick
----------
From: Eugene P. Mosca <mosca@nadn.navy.mil>
To: phys-l@atlantis.cc.uwf.edu
Subject: pressure-energy density
Date: Thursday, September 04, 1997 8:12 AM

Hi Folks,

The Bernouli equation is that

P + (1/2)mv^2 + mgh

where m is the mass per unit volume, is constant along a streamline of a
viscosity-less incompressible fluid undergoing laminar flow. Does
thinking of the pressure P as some kind of pressure-energy density to be
encouraged, or does is lead to later difficulties? Since the fluid is
incompressible, it is clear that P does not represent work per unit
volume
done in compressing the fluid.

----------------------------------------------------------------
Eugene (Gene) P. Mosca Phone 410-293-6659 (Fax 3729)
Physics Department 410-267-0144 Home
572 Holloway Road 610-683-3597 Summer
U.S.Naval Academy Mailstop 9C, Michelson Rm 339
Annapolis MD 21402 email: mosca@nadn.navy.mil
----------------------------------------------------------------