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[Phys-L] Re: Help with Fluids....



As you say, it's the walls. All you need is a free body diagram for
the vase to see this. Not only is this an effective way to explain
it to students, but it may even convince them of the utility of free
body diagrams.

Okay....
Imagine 3 vessles filled with water to the same height resting on a table.
One vessle is a vertical cylinder, one is shaped like a "V", and one is
shaped like an "A". They all have the same area for the base. You've see
the situation before....Pascal's Vases?

Now, I understand that the pressure on each base would be the same, and
therefore the total force on each base would be the same.

I also understand that the "V" shape would contain more total water, and
therefore would weight more, and therefore would exert more total force on
the table.

What I don't understand is how the force on each base is the same, but the
force on the table is not. Is the additional weight of the water
transmitted through the walls of the container to the table via the "edges"
of the base, and that does not count as the force on the base due to the
fluid pressure?

What would be an effective way to explain this apparent paradox to students?

Thanks for the help!
~ Ralph von Philp


--
John "Slo" Mallinckrodt

Professor of Physics, Cal Poly Pomona
<http://www.csupomona.edu/~ajm>

and

Lead Guitarist, Out-Laws of Physics
<http://www.csupomona.edu/~hsleff/OoPs.html>
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