Re: I need someone's brain juice here?

guskz@xxxxxxxxxxx wrote:

>both models seem to be the same:
>
>I also just noticed that even the mechanical press says P1 = P2 (P1=
>P2 + density(h)(g)...thus P1 = P2 + 0), so it's most likely as you said
>neglecting the weight (conteractive force & pressure) of the fluid.

Sorry to *** in, but for the mechanical press there is no
h (for height) or g (for acceleration of gravity) involved.

Hydraulic presses typically use pressures in the
range of 2000 psi to 5000 psi. So in the second case,
the weight of the fluid is neglegible. I don't know why
the term "mechanical press" is used, mechanical presses
use simple levers or rack and pinion, not hydraulic fluid.

The first case of a manometer is complicated by
using an example of Bernoulli venturi to reduce the
pressure in the center tube below atmospheric pressure.

The second case is different because it used high
pressure, usually supplied by pump powered by a powerful
electric motor.

>both midels have pressure applied at both ends and determine the final
>height position of the fluid...#1 h = h2-h1 and #2 h = d1+d2

Actually the second case does not, the cylinders
can be in any orientation, only the pressure matters,
and at 2000 psi, fluid weight or atmospheric pressure
is too small factor to worry about.

In the first case, the pressure drop in the center
tube is actually more related to venturi than to Bernoulli,
although both apply. It is too complicated.

http://www.ce.utexas.edu/prof/kinnas/319LAB/Applets/Venturi/venturi.html

http://www.allbiographies.com/biography-GiovanniBattistaVenturi-33350.html

>h1 & h2 is in relation to the base of the fluid where as d1 & d2 is
>relation to the initial height if both pressures applied on the pistons
>are the same.

Study it again, and notice that there is no height
in the case of the hydraulic press with two pistons and
cylinders.

In the first case, there is no pressure above atmospheric
pressure, so the two cases are not related.

Here is a link to a more technical discussion of
the Bernoulli effect.

http://www.princeton.edu/~asmits/Bicycle_web/Bernoulli.html

I want to thank you for posting this message because
I found a web site that shows the Bernoulli effect in a way that
makes clear how an aircraft wing gets it's lift better than
any I have seen.
I have been arguing off and on for 10 years with
a man in Scandinavia and another in that region that
claim that an airfoil does not get lift due to a lower
pressure on the top surface.
This link shows how the air above a wing moves
faster, meaning the molecules cannot bounce on the
wing as many times, and also strike the airfoil surface
at an angle reducing pressure of impact.
This is a link about the Venturi effect, but
the Bernoulli effect is like just the lower half of the
pipe. Scroll down to the "pipe demo" Java animation.

http://home.earthlink.net/~mmc1919/venturi.html

Study the web pages again and consider just a
slight reduction in pressure in the center tube in the
manometer first case,
and a great pressure throughout both cylinders
and pipes in the hydraulic press second case.

Joe Fischer

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