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

[Adrian Tymes]

On Sat, Mar 30, 2013 at 9:50 PM, spike <spike at rainier66.com> wrote:

> Consider an S-shaped sprinkler suspended from a latex hose, underwater.
> Imagine water is pumped thru the sprinkler in the traditional manner at 1
> ml per second, and we discover the sprinkler rotates positive pi radians.
> 2 ml per second rotates it 2 pi radians and so on.
>
> ** **
>
> Now imagine pumping water thru it backwards.  For any steady flow, we
> observe zero rotation.  If the flow is accelerated backwards at 1 ml per
> second squared, what is the rotation?  If the flow is 2 ml per second
> squared, do we get twice the rotation?  If we use a denser fluid, does it
> require the same flow acceleration to produce a rotation?  Or less?  Or
> more?  Could we use a compressible fluid like air and get similar results?
> Does the shape of the nozzles come into play?  There is a lot of science in
> that simple experimental setup.
>

I suspect simple momentum equations can explain.

If 2 ml per second going in gives double the rotation, then measure the
ml per second coming out, not (directly) the ml per second squared
imparted on the sucked-in water.  A denser fluid would thus increase
acceleration in proportion to its mass...which also explains what
happens if you use air.  The shape certainly comes into play, but that
is subsumed in the measurements; measure the force imparted at
each point of the curve, and you may be able to iterate a formula that
covers the curve, but that is a matter for theory, not experiment.
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