I realized after sending out the previous that some of you would like to see
the rest of the article,so here tis'...more at
howstuffworks.com.......................................Coriolis
accelerations are significant when the Rossby number is SMALL. So, suppose we
want a Rossby number of 0.1 and a bathtub-vortex length scale of 0.1 meter.
Since the earth's rotation rate is about 10^(-4)/second, the fluid velocity
should be less than or equal to 2*10^(-6) meters/second. This is a very small
velocity. How small is it? Well, we can take the analysis a step further and
calculate another, more famous dimensionless parameter, the Reynolds number.
The Reynolds number is = L*U*density/viscosity Assuming that physicists bathe
in hot water the viscosity will be about 0.005 poise and the density will be
about 1.0, so the Reynolds Number is about 4*10^(-2). Now, life at low
Reynolds numbers is different from life at high Reynolds numbers. In
particular, at low Reynolds numbers, fluid physics is dominated by friction
and diffusion, rather than by inertia: the time it would take for a particle
of fluid to move a significant distance due to an acceleration is greater
than the time it takes for the particle to break up due to diffusion. The
same effect has been accused of responsibility for the direction water
circulates when you flush a toilet. This is surely nonsense. In this case,
the water rotates in the direction which the pipe points which carries the
water from the tank to the bowl. Reference: Trefethen, L.M. et al, Nature 207
1084-5 (1965). .........Bob,the wiser,some-what W
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