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Bernoulli and viscosity



The 2000-2001 Physics Olympiad preparation exam (mechanics) has a
question in which water comes out of a bullet hole in a water tower.

<http://helios.physics.utoronto.ca/~poptor/problems00/ps2_mechanics.pdf>

The solution...

<http://helios.physics.utoronto.ca/~poptor/solutions00/pss2_mechanics.pdf>

is a little overly complicated but essentially it calculates the
difference in pressure (inside the tank at the level of the hole vs.
outside the tank at the level of the hole) is rho*g*h (where h is
the depth of the water; the difference in air pressure over height
h is ignored) and sets this equal to the change in kinetic energy
per volume, 1/2 rho*v^2. From this one gets the speed of the water
out the hole.

The problem is that this doesn't seem to work in real life. When
I set up my little demo, my speed is significantly less (i.e.,
my stream doesn't go as far as one would expect). I assume the
problem is due to viscous friction but I'm struggling to get an
estimate on what the actually v should be. I've checked
the PHYS-L archives and the web and could not find anything.

Any help would be appreciated.

____________________________________________
Robert Cohen; rcohen@po-box.esu.edu; 570-422-3428; http://www.esu.edu/~bbq
Physics, East Stroudsburg Univ., E. Stroudsburg, PA 18301