msg@drutx.UUCP (GrahamM) (12/10/85)
Hello all you smart people, Does anyone out there know why water in the sink spins in one direction in the Northern Hemisphere when draining, and in the other direction in the Southern Hemisphere? Does this phenomenon have anything to do with the Corealis (sp?) force? Please respond via e-mail. Thank you. -- Matt Graham ihnp4!drutx!msg "A bachelor is a man who looks before he leaps, and then does not leap"
jim@alberta.UUCP (Jim Easton) (12/13/85)
> > Does anyone out there know why water in the sink spins in one direction > in the Northern Hemisphere when draining, and in the other direction > in the Southern Hemisphere? It doesn't. The idea is perpetrated by people who find the idea attractive and are ignorant about the magnitude of the forces involved. Weather systems and long range ballistics are affected because of their size and the speed which gun shells travel but water in a sink is too small a system for Coriolis acceleration to have any significant effect. > Does this phenomenon have anything to do with the Corealis (sp?) force? No - It has to do with conservation of angular momentum. You don't feel Coriolis acceleration when you're walking down the street or driving on the highway. Why would you expect the water in a sink to feel it. Granted that it is not zero but is overwhelmed by orders of magnitude by other forces. Given a circular tub with a drain hole in the middle. Water draining out of that hole will almost always form a whirlpool but that is because the body of water almost always has some initial (albeit small) angular momentum about the hole which determines the direction. Don't take my word for it. There is nothing like a good experiment to debunk this sort of nonsense. The tub I tried it on was circular with the drain hole in the middle about a foot deep and about 3 feet across. The barest perceptible motion would determine the direction of any whirlpool that developed. It literally took hours for the water to settle sufficiently to not form any whirlpool. Jim Easton (..!alberta!jim)
bobm@rtech.UUCP (Bob Mcqueer) (12/15/85)
> >> Does this phenomenon have anything to do with the Corealis (sp?) force? > > No - It has to do with conservation of angular momentum. > > Given a circular tub with a drain hole in the middle. Water draining out > of that hole will almost always form a whirlpool but that is because the > body of water almost always has some initial (albeit small) angular momentum > about the hole which determines the direction. > > Don't take my word for it. There is nothing like a good experiment to > debunk this sort of nonsense. The tub I tried it on was circular with the seconded. I just now went to the bathroom sink, filled it a few times, and by swishing the water around in different directions before opening the drain managed to induce whirlpools in both directions. Also observe that if you do this the whirlpool forms a lot sooner than in a still sinkfull of water. Of course, to be sure I wasn't cancelling out the "corealis" effect, I would have to do some more rigorous experimenting, but .... What I wanted to add was that this little tale is usually told concerning toilets, and if you look, the water coming out from under the lip of the bowl is usually sent out at a slant, inducing a very definite direction for the whirlpool (for good design reasons, probably - think about it). If there WERE any differences between hemispheres, this would certainly cancel them out. I wouldn't be surprised if the tale got started because makers of toilets in different countries slant the water jets in different directions for some arcane reason, or more likely, because clockwise was as good as counterclockwise, and somebody flipped a coin. Bob McQueer ihnp4!amdahl!rtech!bobm
jbell@grofe.DEC (Jeff Bell) (12/17/85)
[I don't know, but I always get this line anyways] > Given a circular tub with a drain hole in the middle. Water draining out > of that hole will almost always form a whirlpool but that is because the > body of water almost always has some initial (albeit small) angular momentum > about the hole which determines the direction. I once read someplace that it is possible to see the effect in a draining sink. The hard part according to the article is trying to eliminate the vorticity left from filling it. The person doing the experiment had to wait for four hours before getting consistent results. After that long of a wait, it went in the right direction 80% of the time and the wrong direction 20%. I think that it was in Jearl Walker's Scientific American Column about 2 or 3 years ago, but I may be mistaken. Jeff Bell Arpa: jbell%tallis.DEC@decwrl.ARPA UUCP: ????decwrl!rhea!tallis!jbell "Replace this line with Your Favorite Disclaimer"
halle@hou2b.UUCP (J.HALLE) (12/20/85)
Contrary to what many have claimed, the coriolis force does exert a real influence in determining the direction of spiral down the drain. This fact has been experimentally shown many times. There is a short film I saw in Fluids class or Frosh Physics umpteen years ago that recorded one of these experiments. A large tub was filled so that the induced motion would be contrary to the expected motion. The tub sat undisturbed for hours. When a plug was pulled, the water eventually spiraled the way expected. The experiment was repeatable.
steve@jplgodo.UUCP (Steve Schlaifer x3171 156/224) (12/23/85)
> Contrary to what many have claimed, the coriolis force does exert > a real influence in determining the direction of spiral down the > drain. This fact has been experimentally shown many times. There > is a short film I saw in Fluids class or Frosh Physics umpteen years > ago that recorded one of these experiments. A large tub was filled > so that the induced motion would be contrary to the expected motion. > The tub sat undisturbed for hours. When a plug was pulled, the water > eventually spiraled the way expected. The experiment was repeatable. The above mentioned experiment is incomplete. All it *proves* is that the water in the tub in question spiraled out in the *expected* direction. It is still possible that the spiraling was due to small imperfections in the tub itself which caused a preferred spiraling direction. What is needed for this to be a more complete demonstration is to take the tub to the other hemisphere and repeat the experiment there. If the direction of spiral reverses then a good demonstration of the effect has been made.
meister@linus.UUCP (Phillip W. Servita) (12/23/85)
>Contrary to what many have claimed, the coriolis force does exert >a real influence in determining the direction of spiral down the >drain. This fact has been experimentally shown many times. There >is a short film I saw in Fluids class or Frosh Physics umpteen years >ago that recorded one of these experiments. A large tub was filled >so that the induced motion would be contrary to the expected motion. >The tub sat undisturbed for hours. When a plug was pulled, the water >eventually spiraled the way expected. The experiment was repeatable. I would be more willing to believe this if you could provide me with the answer to this: What setup did they use such that they could "pull the plug" without imparting ANY additional momentum to the fluid inside? even if we allowed a "magic plug" which simply vanished at the utterance of "Poof!", the slightest imperfection in the drain itself would allow Good Old Gravity to impart some initial circulatory momentum to the fluid which would still outweigh the Coriolis force. And of course, this would be repeatable. -the venn buddhist -- ------------------------------------------------------------- "they forcibly extracted the word 'but' from his vocabulary, and locked him in a room with 10 economists..." ------------------------------------------------------------- -the venn buddhist
jim@alberta.UUCP (Jim Easton) (12/24/85)
> Contrary to what many have claimed, the coriolis force does exert > a real influence in determining the direction of spiral down the > drain. This fact has been experimentally shown many times. There > is a short film I saw in Fluids class or Frosh Physics umpteen years > ago that recorded one of these experiments. A large tub was filled > so that the induced motion would be contrary to the expected motion. > The tub sat undisturbed for hours. When a plug was pulled, the water > eventually spiraled the way expected. The experiment was repeatable. Nobody said that Coriolis acceleration was zero - just very small for small bodies of water. Given a "large" (how large was it?) tub of water under carefully controlled conditions one might observe a correlation. However that's a long way from water flushing down toilets and draining out of bathtubs. Let's try to keep a sense of perspective. Jim Easton (..!alberta!jim)
jp@lanl.ARPA (12/24/85)
To eliminate the possibility of mechanical bias in this experiment it ought to be repeated in the southern hemisphere to see if the direction of the rotating water changes.