I am sorry about all the typos. “that the,” should be “then the”, “the the” should read “The tube,” and “cajoles,” should read “cajoled.”
Sheesh, I did reread, I just read what I thought I wrote.
Sorry Again
I’m not quite sure that what you describe is exactly what Bermoulli was talking about.
While it’s very true that the Bernoulli principle involve pressure differential on two sides of an object causing the object to move in the direction of the lower pressure – I thought the key element Bernoulli explains was why there is lower pressure (airplane wing shape and distance for flowing air to travel being greater on top than on the bottom). So I don’t think the pipe represents the Bernoulli principle so much as it it MIGHT just represent differential pressure. (I say MIGHT only because I was all set to buy into the standing-still theory until you messed it up for me again!)
- Rick
Bricker:
In the experiments, did they apply a LOT of suction in one case (more than one atmosphere and enough to cause cavitation.) If they did, it might very well move forward.
Also, if the S were immersed in a relatively small pool of water, it might create a whirlpool effect that would move the sprinkler.
How about:
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It doesn’t move because God doesn’t want it to.
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According to the Heisenberg Uncertainty principle, it is possible to either know the sprinkler heads location or spin, Never both. Since we know the sprinkler is underwater, it is impossible to determine spin.
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The sprinkler head won’t move until you observe it.
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When you put the sprinkler head under water the universe splits in three, in order to actualize all possibilities.
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Feynman is screwing with us.
I’m glad this debat brought new people!
Often wrong… NEVER in doubt
Bernoulli has nothing meaningful to do with this
Re the experiments: The UMD experiment was more skillfully designed, and goes along with an article referenced on one of the pages I linked to - I didn’t find a link to the article, but it was published in a physics journal so it is findable and believable.
Zor, your linear momentum argument is good, but you are missing the angular momentum factor - this is why the sprinkler goes backwards if you remove friction. It only goes fast enough to preserve angular momentum, not as fast as if you were squirting water out.
Douglips:
I Checked links. I still say Sprinkler doesn’t move, and if it does we all die.
Marilyn was already defeated by Cecil in another column, and as such lacks the infallibilty of the Dopers.
Often wrong… NEVER in doubt
I would also mention that the experiment exploded in one of those links.
As I warned at the outset this is an extremely dangerous avenue of inquiry.
Perhaps there are some things man was not meant to know.
Heh. heh. heh.
Often wrong… NEVER in doubt
Let me try again, please. Below is an small little gif I created illustrating my argument. If you don’t like the image, I’ll happily kill it.
http://www.pages.about.com/earldavid/SDMBinlet.gif
The red arrows illustrate the flow across the tube’s thickness. I maintain that this flow results in a lower pressure area.
Dammit, I followed the FAQ to the letter. The image is here:
Mr. Thin Skin:
I’m sorry, but I can’t see your GIF.
In an earlier reference I made to low pressure underwater and the movement of a siphon towards an obstacle I misspoke.
The currents pull the pebble and siphon together, not the pressure.
The foundation of hydraulics is that water is not compressible.
The pressures remain exactly the same despite the currents.
I get “The page you select is not currently available.”
MIT and physicists worldwide disagree. We are being thwarted by forces beyond are comprehension.
Perhaps this experiment represents a glitch in the software of life.
We need to appeal to a higher power.
Unca’ Cece, please? Pretty please with sugar on top?
Often wrong… NEVER in doubt
Actually, this is a good point.
There have been reasoned, erudite analyses for both the “stays still,” “moves forward,” and “moves backwards,” camps.
Perhaps if Ed is reading this, he could bring it to Unca Cecil’s attention. Since MIT and U of M seem stymied, we clearly must appeal to a higher authority.
- Rick
We must now all bow our heads, and invoke the ritual chant:
Ahem,
Repeat after me.
“I will send you a sawbuck. I will send you a sawbuck. I will send you a sawbuck.”
Often wrong… NEVER in doubt
This is an interesting series of explanations. My initial reaction when reading the problem statement was that the device would not move, and I have not read anything that would change my opinion on that.
I have no explanation of this but here are my thought processes:
First, imagine the “normal” sprinkler spraying water from the nozzles into the air. Now imagine air is being sprayed through the system instead of water. The sprinkler would still spin in the same direction although probably slower (depending on the pressure used). This made me think it was a friction problem not a suction vs. pressure problem. the pressure of the water spraying from the ends overcomes the friction of the apparatus itself and the air it is moving through. If you reverse the flow under these conditions, the movement will stop (just as the one of the previous posters described using the blow dryer/vaccuum cleaner example).
Now take this a step further to the underwater scenario. It seems if you pump water through the system, it will only move if the pressure overcomes the friction resistance of the apparatus and the water it is moving through (probably will move slowly in this case). Now reverse the flow, but not by suctioning through the device, but by increasing the pressure on the pool it is in (assuming it is a closed system, except for the outlet from the apparatus). It seems obvious to me in this case that the apparatus will not move.
Feel free to shoot this entire post full of holes.
My God, it’s full of stars.
Scylla writes:
Your ‘column of air will destroy us’ is both amusing and pointless to this discussion. Either you did not check links, or I did not provide enough. I will remedy that below. The fact is that if the experiment is done with little friction, the sprinkler does revolve backwards (opposite squirt mode.)
Scylla again:
Which is exactly why I linked to a page explaining why she was wrong.
The experiment has been done, and was published in the American Journal of Physics, a well respected scientific journal. If you go to the AJP’s search page you can search for ‘Feynman AND sprinkler’ (here is a link to the results, but it is long and may not work: [Try it](http://ojps.aip.org/AIPcgipath/doc/search-AJPIAS/disk3/journals/journal_cgi/search?origquery=&vdk_query=&page=1&chapter=0&docdisp=0&smode=strresults&query_type=search&KEY=AJP IAS&CURRENT=NO&ONLINE=NO&SMODE=strsearch&possible1=Feynman&possible1zone=article&bool1=and&possible2=sprinkler&possible2zone=article&fromyear=&frommonth=&fromday=&toyear=&tomonth=&today=&fromvolume=&tovolume=&fromissue=&toissue=&sort=rel&maxdisp=10&threshold=0&%5BSearch%5D.x=58&%5BSearch%5D.y=12))
You will find 5 documents that have been published over the years regarding this issue.
The definitive article(s) are (links to abstracts may work)
[ul][li]**American Journal of Physics – July 1989 – Volume 57, Issue 7, pp. 654-657 **[/li][The Feynman inverse sprinkler problem: A demonstration and quantitative analysis](http://ojps.aip.org/AIPcgipath/doc/tomonth/disk3/journals/journal_cgi/search?KEY=AJPIAS&CURRENT=NO&ONLINE=NO&smode=display&docnum=4&coden=AJPIAS&vol=57&iss=7&page=1&chapter=0 &fpage=654&seqno=1&issuedate=July%2B1989&journal=American+Journal+of+Physics&numret=5&sort=rel&maxdisp=10&docnum=4&origquery=%28%28Feynman%29++%3Cand%3E+sprinkler%29+&threshold=0&a bscall=strresults&logid=YES&allprl=0&pjournals=&pyears=)
Richard E. Berg and Michael R. Collier
Lecture–Demonstration Facility, Department of Physics and Astronomy, University of Maryland, College Park, Maryland 20742
[li]American Journal of Physics – April 1991 – Volume 59, Issue 4, pp. 349-355[/li]
[The Feynman inverse sprinkler problem: A detailed kinematic study](http://ojps.aip.org/AIPcgipath/doc/tomonth/disk3/journals/journal_cgi/search?KEY=AJPIAS&CURRENT=NO&ONLINE=NO&smode=display&docnum=2&coden=AJPIAS&vol=59&iss=4&page=1&chapter=0 &fpage=349&seqno=1&issuedate=April%2B1991&journal=American+Journal+of+Physics&numret=5&sort=rel&maxdisp=10&docnum=2&origquery=%28%28Feynman%29++%3Cand%3E+sprinkler%29+&threshold=0& abscall=strresults&logid=YES&allprl=0&pjournals=&pyears=)
Michael R. Collier, Richard E. Berg, and Richard A. Ferrell
Department of Physics and Astronomy, University of Maryland, College Park, Maryland 20742[/ul]
Excerpt from the abstract of the first article:
Does that satisfy you? I feel no impending implosion from a column of miffed atmosphere.
The links to the abstracts and search results above are in fact broken. To read the abstracts or order the articles for your very own selves, go to the AJP Search page and search for Feynman AND sprinkler.
Enjoy.
I think I figured out how to link to these darn things.
[ul][li]The Feynman inverse sprinkler problem: A demonstration and quantitative analysis[/li]Richard E. Berg, Michael R. Collier
American Journal of Physics, Volume 57, Issue 7, pp. 654-657
[li]The Feynman inverse sprinkler problem: A detailed kinematic study[/li]Michael R. Collier, Richard E. Berg, Richard A. Ferrell
American Journal of Physics, Volume 59, Issue 4, pp. 349-355[/ul]
I think I figured out how to link to these darn things.
[ul][li]The Feynman inverse sprinkler problem: A demonstration and quantitative analysis[/li]Richard E. Berg, Michael R. Collier
American Journal of Physics, Volume 57, Issue 7, pp. 654-657
[li]The Feynman inverse sprinkler problem: A detailed kinematic study[/li]Michael R. Collier, Richard E. Berg, Richard A. Ferrell
American Journal of Physics, Volume 59, Issue 4, pp. 349-355[/ul]