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Re: reverse water sprinkler



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!