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

[spike]

>. On Behalf Of John Clark
Subject: Re: [ExI] underwater sprinkler, was: RE: Musical instruments in
space

 

On Sun, Mar 31, 2013 at 12:50 AM, 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.


>.Blowing and sucking are not symmetrical processes, that's why it's easy to
tell if a film of a sprinkler is running forward or backward and why you can
blow water as high as you want but no matter how powerful the pump is on the
surface of the earth you can only suck water about 25 feet. In one case a
pump is increasing pressure inside the narrow sprinkler nozzle causing the
water to move in just one direction, perpendicular to the nozzle opening.
But in the other case when the pump is decreasing pressure inside the small
nozzle the water moves inside because of the outside pressure produced by
the weight of the water and the air on top of it, and that pressure is
coming from all directions so the water is coming through the opening from
all directions too, and so no narrow beam of water is formed and no net
torque is produced.

  John K Clark



Ja, agreed John however your commentary (I think) applies to steady state
and integration over time torque equals zero, which is what I think you
meant by "no net torque is produced."  Yet we know that increasing and
decreasing flows do create a torque.  Try it!  Bend some copper tube, attach
to a plumber's T, some latex tube, a reversible DC motor water pump (all of
which are available at the local hardware store for about 30 bucks for all
of it) and try it.

 

But I am asking the question from the point of view of a controls engineer.
Imagine you are trying to control the position of the S, and all you have is
the reversible water pump.  Until we can write equations to describe that
motion, we cannot derive a control system.  We can't use any of those wicked
cool mathematical tools we moderns have in our bag of controls magic tricks.


 

I have tried to derive those equations, and I have failed so far.  But if
you manage to derive the equations of motion, I can show you how to solve
them and make a controls system.  Then we can rig up a physical-world
analog, test it to see if we know what we are doing, or if we are just a
bunch of controls wannabes.  {8^D   If someone here manages the derivation
and it turns out simple, I will be highly annoyed.  But I will get over it.


 

Notice the indistinguishable-from-god Richard Feynman himself mentioned the
underwater sprinkler in his book Surely You're Joking, but didn't offer the
equations of motion, or even suggest they found them.  The bigshot future
Nobel physicist himself immediately surrendered and went straight to
physical-world analog and lab setups, which failed explosively.  (Get
Feynman's book, it's hilarious, page 52 in the Bantam edition, or if another
edition, the page right before the chapter titled "Meeeeeeee!")

 

I have half a mind to contact some mechanical engineering professors up at
Stanford (or that other local school, Berk something or other) see if their
students want to take up the challenge.  Who would have thought, such a
simple little mechanical device with only one moving part could be so
educational and challenging?

 

spike

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.extropy.org/pipermail/extropy-chat/attachments/20130331/dd085ea1/attachment.html>