John Mallinckrodt wrote about how we can relate the pressure with the
density. This is the way I have viewed it and I like it, so I agree
with JM. His posts have clarified things for me.
John Denker seemed to be critical of JM's cause/effect between density
and pressure. As some people know, I agree with JD's concerns about
cause/effect. However, in this case, I don't think JM was necessarily
implying a cause/effect. Rather, it is more that the pressure
distribution must mirror, for the most part, the density distribution.
This gives us a clearer picture of what is happening on the microscale.
In other words, rather than thinking that the particles have a different
velocity along z than along y or x, simply envision how dense the fluids
particles are in a particular region.
Please correct me if this is incorrect.
P.S. William Robertson wrote that the original question was complicated
by the fact that he apparently chose a phenomenon where Bernoulli
doesn't apply. I, for one, think the phenomenon WR presented was
perfect -- as it shows that our intuition about the fluid density
(higher density inside the tube than outside) is better at inferring
pressure differences than blindly assuming that faster always means
higher pressure.
----------------------------------------------------------
Robert A. Cohen, Department of Physics, East Stroudsburg University
570.422.3428 rcohen@po-box.esu.edu http://www.esu.edu/~bbq