Re: reverse water sprinkler

[Cliff Parker <cparker@EMPOWERING.COM>]

> I (and my students!) have a lot of questions, but first of all:
>
> When I think about this from a newtons 3rd perspective I get one answer:
> suck and blow both go clockwise.  I'm not much on fluids, but my other
> approach involved some Bernoulli-babble (which I'd be embarrassed to quote
> here) and yielded: suck and blow both go counterclockwise.   Each
> explanation is clearly wrong!
>
> Does anyone have a satisfactory answer?  Surely I am missing something
> obvious!

Cool problem.  I had not heard of it before.  But Feynman's "Surely you're
joking" is next on my list.  It seems to me your students sort of have it
correct.  The pressure differences between the nozzle's front and back cause a
net force on the back side of the sprinkler that push it in the clockwise
direction.  I don't believe that what happensinternally changes the external
motion of the sprinkler.

Cliff Parker

> David Strasburger
> Noble & Greenough School
> Dedham MA
>
> PS: in the wake of the tennis ball discussion, let me assure you that the
> observations described herein have been recorded faithfully, carefully,
> and repeatedly!  If anyone is truly in doubt we can probably figure out
> how to post a video clip to the web!