DrWho Posted December 16, 2005 Share Posted December 16, 2005 EDIT2 - I changed my mind.... i have no clue... [H] Quote Link to comment Share on other sites More sharing options...
Ray Garrison Posted December 16, 2005 Share Posted December 16, 2005 Wow... That guy had a gift. For such a seemingly simple question... Google feynman sprinkler under water You'll find advanced physics departments at various universities have been arguing this for years, and there appears to be no diffinitive answer to the question. Wow... Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted December 16, 2005 Share Posted December 16, 2005 Well done Gil. Here is another problem from Richard Feynman that he used to start arguments among physicists at parties. It's obvious that the sprinkler nozzles below will rotate clockwise when water flows out of the nozzles under pressure. If you submerge the sprinkler in a tank of water and suck water into the sprinkler (reversing the flow), which way will the nozzles rotate? it would not move... water is denser than air as it pushed the air. Since the environment is trying suck is water and it has the same density all around it would not move. Quote Link to comment Share on other sites More sharing options...
Fish Posted December 16, 2005 Share Posted December 16, 2005 That cracked me up.Steelers smiley that is. Quote Link to comment Share on other sites More sharing options...
sputnik Posted December 16, 2005 Share Posted December 16, 2005 Wow... That guy had a gift. For such a seemingly simple question... Google feynman sprinkler under water You'll find advanced physics departments at various universities have been arguing this for years, and there appears to be no diffinitive answer to the question. Wow... Feynman was truly amazing and a genius in every sense of the word. This was a somewhat famous teaser that he would toss out and then argue convincingly that the nozzle would go a certain direction and then he could change his argument to convince just about anyone that the nozzle would go the other way. But here is the explanation: When water is jetting out of the nozzle, it has a single direction and magnitude (relative to the nozzle) that results in a force and the momentum of the water jet is equal to the momentum that spins the nozzle. But in the case of reverse flow (suction), the flow of water toward each nozzle point is radial and isotropic (of equal magnitude in all directions) so that all the forces cancel each other out and the resultant force on the nozzle is negligible and so there is no rotation. The nozzle may shake but won't rotate. The story goes that Feynman was banned from the cyclotron lab at Princeton after he pressurized a water bottle with a sprinkler in it that subsequently exploded. Quote Link to comment Share on other sites More sharing options...
Ray Garrison Posted December 16, 2005 Share Posted December 16, 2005 Surprizingly enough, the answer is really not so simple... The Feynman inverse sprinkler problem: A detailed kinematic study American Journal of Physics -- April 1991 -- Volume 59, Issue 4, pp. 349-355 http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=AJPIAS000059000004000349000001&idtype=cvips Abstract This paper represents an extension of the results of an original paper on the subject [Am. J. Phys. 57, 654657 (1989)]. Here an experiment, originally performed by Titcomb et al., to demonstrate the inverse sprinkler effect is described and analyzed. It is shown that, in a water reservoir, the angular momentum of the sprinkler head is approximately equal and opposite that of the fluid in the sprinkler arms. However, in an air reservoir, one must consider the effects of both turbulence and the motion of the reservoir. Both effects result in a steady-state acceleration of the inverse sprinkler in a direction opposite that of the normal sprinkler. Also presented is a more detailed analysis than the one given in the original paper to explain the steady-state behavior of the inverse sprinkler. Quote Link to comment Share on other sites More sharing options...
DrWho Posted December 16, 2005 Share Posted December 16, 2005 Ya know....this is one of those times where you could argue the physics all you want, but it would be so much easier to just try it and see what happens [] You know, that whole experimental thing that drives all the theories we're using to come to a conclusion, lol [] Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted December 17, 2005 Share Posted December 17, 2005 I concluded my answer just because the water is pushing across air. Kinda like a water bottle rocket where the water is pressured and is pushing the air. In reverse since there is equal suction, and equal density, it would not move. I did not google it I just pondered for a bit. Quote Link to comment Share on other sites More sharing options...
WMcD Posted December 17, 2005 Share Posted December 17, 2005 Hmm, maybe the joke is on me. I should Google before thinking. BTW I have noted that when you put a garden hose nozzel in a pool the reaction is reduced, but not eliminated. Also, when I was a little kid I did fill up the little pool with a rotating sprinkler. It did spin underwater, to my recall. This makes sense because Sea-Doos use underwater jets. I can see that part of the issue in suction on the lawn sprinkler is that we reverses the flow. But we have not reversed the geometry of the conical converging nozzle. So I wonder what happens if we do that. Put a diverging nozzle on the arms. Envision Horn Ed's ears (the avitar) on the ends. Smile I would think that the studies are not saying we can never devise a suction operated underwater sprinkler turbine. If we put a pin wheel in a bathtub drain, it would spin. That is how the Hoover Dam makes electricity. Gil Quote Link to comment Share on other sites More sharing options...
sputnik Posted December 18, 2005 Share Posted December 18, 2005 Hmm, maybe the joke is on me. I should Google before thinking....... Gil That's an interesting point. I wonder if Google will impact they way we think and retain knowledge the way handheld calculators seem to have affected the way we do math. It's too easy just to Google up an answer for just about anything rather than flex our brains a bit. Maybe it frees us to think in more abstract terms but does it also create an intellectual dependence on technology over analytical thinking? Or just thinking for the fun of it. That's one of the reasons that I admire guys like Richard Feynman. He won the Nobel Prize for his work in quantum electrodynamics among his other accomplishments that few people could really understand and yet he still pondered the physics of something as simple as a lawn sprinkler. Anyway, here is a neat math problem I found (using Google) when helping my nephew with his homework. Three balls are placed inside a cone such that each ball is in contact with the edge of the cone and the next ball. If the radii of the balls are 20 cm, 12 cm, and r cm respectively, what is the value of r? Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted December 18, 2005 Share Posted December 18, 2005 4? and no google Quote Link to comment Share on other sites More sharing options...
sputnik Posted December 18, 2005 Share Posted December 18, 2005 4? and no google Good try using the pythagorean theorem (that would've been really cool) but that's not the right answer. [] Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted December 18, 2005 Share Posted December 18, 2005 is it a whole number? Quote Link to comment Share on other sites More sharing options...
sputnik Posted December 18, 2005 Share Posted December 18, 2005 No, it's not whole number. Added: Speaking of the pythagorean theorem, I think this is the coolest proof of it. Quote Link to comment Share on other sites More sharing options...
customsteve01 Posted December 18, 2005 Share Posted December 18, 2005 I would say 7.2 But I bet thats not right. Steve Quote Link to comment Share on other sites More sharing options...
sputnik Posted December 18, 2005 Share Posted December 18, 2005 I would say 7.2 But I bet thats not right. Steve You're wrong (about being wrong). 7.2 is the right answer. [] Using similar triangles, (12 + r)/(12 - r) = 32/8 = 4. ? 12 + r = 48 - 4r ? 5r = 36 ? r = 7.2 cm. Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted December 18, 2005 Share Posted December 18, 2005 bah Quote Link to comment Share on other sites More sharing options...
customsteve01 Posted December 18, 2005 Share Posted December 18, 2005 Wow thats cool, but I got the answer a lot easier. 20/12=1.6666666666666667 12/1.666666666666667=7.2 my way was way too easy thats why I thought I was wrong. Steve Quote Link to comment Share on other sites More sharing options...
Jay481985 Posted December 18, 2005 Share Posted December 18, 2005 heh I did it the opposite way and got a .7 and mutiplied that by 12 and got 8.4.....and then halfed it 4.2 but thought oh well 4...... What sputnik did was a three piece system using pythagoream's theorem (which btw is still a theory that works in most cases). Bah I forgot to do it that way. I wasn't thinking that that cone would be a similiar triangle. Quote Link to comment Share on other sites More sharing options...
Ray Garrison Posted December 19, 2005 Share Posted December 19, 2005 Here's a puzzle American Can used to give their managers years ago - was part of a packet with the famous "Connect these 9 dots with four lines without lifting your pencil from the page" puzzle... Here is a sequence of digits. What pattern are they following, and what is the next number(s) in the sequence? 8 5 4 9 1 7 6 brief aside - I felt a little depressed when I saw a few references to thrust moving objects because the exiting mass was "pushing" on something... rockets do fly in outer space, ya know... what happened to basic science classes? Quote Link to comment Share on other sites More sharing options...
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