[ExI] underwater sprinkler, was: RE: Musical instruments in space

[Adrian Tymes]

On Sat, Mar 30, 2013 at 1:59 PM, spike <spike at rainier66.com> wrote:

> Regarding the underwater sprinkler, during the time in which the flow rate
> is increasing, there is a counter-rotation.  During the time in which the
> flow rate is decreasing, the borrowed angular momentum must be paid back,
> exactly with no interest.  So during that phase, there is a rotation in the
> same direction as the above-water sprinkler.
>
>
>
> Some of you mathematical hotties, do explain that observation please,
> using differential equations, or whatever is your favorite mathematical
> technology, including even a digital model or a Matlab sim.  If you manage
> it, the grand prize will be yours: my sincere everlasting admiration.
>

Who needs equations?

The spin is "borrowed from" or "paid back to" the surrounding water.
The above-water use case's spin isn't just for show; the water, by
pushing against the sprinkler and sending it spinning, is in exchange
pushed further.  Likewise, underwater, the water going through the
sprinkler is the medium by which angular momentum is transferred,
and contains the counter-rotation.  (The center of the sprinkler is not
a mathematical point, so there is some spin there.  And by friction,
water that will be going into the sprinkler can affect the motion of
water that will not.)
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