Date: Sat, 8 Apr 1995 11:07:49 -1000 From: Colin_Douthwaite@equinox.gen.nz (Colin Douthwaite) Message-Id: <3m6tv5$pug@southern.co.nz> Organization: Southern InterNet Services Subject: Re: Does water flow clockwise or counter-clockwise when going down the drain?? R.K.S. Hankin (rksh@eng.cam.ac.uk) wrote: : |There is an extremely interesting part of the physics FAQ discussing : |why the above is *completely* incorrect. I quote: : | : | : |Which Way Will my Bathtub Drain? updated 16-MAR-1993 by SIC : |-------------------------------- original by Matthew R. Feinstein |Because the earth rotates, a fluid that flows along the earth's |surface feels a "Coriolis" acceleration perpendicular to its velocity. |In the northern hemisphere low pressure storm systems spin |counterclockwise. |In the southern hemisphere, they spin clockwise |because the direction of the Coriolis acceleration is reversed. |This effect leads to the speculation that the bathtub vortex that |you see when you pull the plug from the drain spins one way in the |north and the other way in the south. > Now, can we talk about something else? Yes :-) It has been suggested that single-line fighter kites spin in the opposite direction if the "spin" settings of the kite bridles are unchanged but the kite is flown in a different hemisphere. Clockwise spin in the Northern hemisphere and anti-clockwise spin in the Southern hemisphere. Due to those pesky storm-system spins eh ? :-) Bye, = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sun, 9 Apr 1995 06:30:04 -1000 From: andrew@tug.com (Andrew Beattie) Message-Id: Organization: /usr/lib/news/organisation Subject: Re: Does water flow clockwise or counter-clockwise when going down the drain?? Colin_Douthwaite@equinox.gen.nz (Colin Douthwaite) writes: >: |Which Way Will my Bathtub Drain? updated 16-MAR-1993 by SIC >It has been suggested that single-line fighter kites spin in the >opposite direction if the "spin" settings of the kite bridles are >unchanged but the kite is flown in a different hemisphere. Clockwise >spin in the Northern hemisphere and anti-clockwise spin in the >Southern hemisphere. Hmm... Interesting suggestion, but somehow I doubt that Coriolis will be sufficient to overcome other significant forces on the kite, such as: - The balance of the kite when tension is released - Twist in the line Note that accomplished fliers can control which way the kite turns... Andrew -- New to rec.kites? START HERE! | To: www@kfs.org send an email message like this->| Subject: service /-\ () >< () |\/| () >< () /-\ | http://www.kfs.org/kites/welcome/index.html = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Mon, 10 Apr 1995 07:45:40 -1000 From: skip@taygeta.oc.nps.navy.mil (Skip Carter) Message-Id: Organization: Naval Postgraduate School, Monterey Subject: Re: Does water flow clockwise or counter-clockwise when going down the drain?? In article <3m6tv5$pug@southern.co.nz>, Colin_Douthwaite@equinox.gen.nz (Colin Douthwaite) writes: |> R.K.S. Hankin (rksh@eng.cam.ac.uk) wrote: |> |> : |There is an extremely interesting part of the physics FAQ discussing |> : |why the above is *completely* incorrect. I quote: |> : | |> : | |> : |Which Way Will my Bathtub Drain? updated 16-MAR-1993 by SIC |> : |-------------------------------- original by Matthew R. Feinstein |> |> |> |> |Because the earth rotates, a fluid that flows along the earth's |> |surface feels a "Coriolis" acceleration perpendicular to its velocity. |> |In the northern hemisphere low pressure storm systems spin |> |counterclockwise. |> |In the southern hemisphere, they spin clockwise |> |because the direction of the Coriolis acceleration is reversed. |> |This effect leads to the speculation that the bathtub vortex that ^^^^^^^^^ |> |you see when you pull the plug from the drain spins one way in the |> |north and the other way in the south. |> |> Sorry, but this speculation is NOT CORRECT except on geophysical time and space scales !!!! Any such effect reported in a bathtub has nothing to do with the earths rotation. The critical scale parameter, the Rossby radius of deformation, is must be smaller than the length scales involved in the flow before the Coriolis acceleration has any significant effect on the flow. The (external) Rossby radius of deformation is, R = sqrt( g H ) / f ( H vertical scale of flow, g gravity) where f = 2 W cos( latitude ) (W = angular rotation rate). For midlatitudes on earth, f ~ 1.0e-4. If we assumed a 1M deep bathtub, then R ~ 3.1e4, i.e. 31 KM. In other words the Coriolis force has NO EFFECT on the direction of flow of water in a bathtub 1M deep unless the tub is AT LEAST 31 KM across. -- Everett (Skip) Carter Phone: 408-656-3318 FAX: 408-656-2712 Naval Postgraduate School INTERNET: skip@taygeta.oc.nps.navy.mil Dept. of Oceanography, Code OC/CR UUCP: ...!uunet!taygeta!skip Monterey, CA. 93943 WWW: http://taygeta.oc.nps.navy.mil/skips_home.html = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Wed, 12 Apr 1995 09:03:07 -1000 From: coreykite@aol.com (Coreykite) Message-Id: <3mh85b$ik2@newsbf02.news.aol.com> Organization: America Online, Inc. (1-800-827-6364) Subject: Re: Does water flow clockwise or counter-clockwise when going down the drain?? >Re; Which way does the water flow down under? On my recent visit, while attempting to determine this specific question, I was dismayed to find most toilets of the sluice-flow variety rather than the whirling style common in the states. The question remains unresolved. BTW, I do not bathe in tub, I am a shower kind of guy. aoxomoxoa coreykite@aol.com = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 13 Apr 1995 03:07:45 -1000 From: mr.nasty@ix.netcom.com (Frank Kenisky) Message-Id: <3mj7n1$dq4@ixnews2.ix.netcom.com> Organization: Netcom Subject: Re: Does water flow clockwise or counter-clockwise when going down the drain?? In <3mh85b$ik2@newsbf02.news.aol.com> coreykite@aol.com (Coreykite) writes: > >>Re; Which way does the water flow down under? >On my recent visit, while attempting to determine this specific question, >I was dismayed to find most toilets of the sluice-flow variety rather than >the whirling style common in the states. The question remains unresolved. >BTW, I do not bathe in tub, I am a shower kind of guy. Does that mean you wait till it rains to bathe? -- >>>>>>>>>>>>>>>>>|||||||||||||||||||||||||<<<<<<<<<<<<<<<<< Confucius say: "Man who live in glass house should dress in basement. >>>>>>>>>>>>>>>>>|||||||||||||||||||||||||<<<<<<<<<<<<<<<<< = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 13 Apr 1995 10:56:18 -1000 From: Adrian Pierorazio Message-Id: Organization: Queen's University, Kingston Subject: Re: Does water flow clockwise or counter-clockwise when going down the drain?? On Mon, 10 Apr 1995, Skip Carter wrote: > In article <3m6tv5$pug@southern.co.nz>, Colin_Douthwaite wrote: > Sorry, but this speculation is NOT CORRECT except on geophysical time > and space scales !!!! Any such effect reported in a bathtub has > nothing to do with the earths rotation. > > The (external) Rossby radius of deformation is, > > R = sqrt( g H ) / f ( H vertical scale of flow, g gravity) > > > where f = 2 W cos( latitude ) (W = angular rotation rate). > > For midlatitudes on earth, f ~ 1.0e-4. > > If we assumed a 1M deep bathtub, then R ~ 3.1e4, i.e. 31 KM. In other words the Coriolis > force has NO EFFECT on the direction of flow of water in a bathtub 1M deep unless the > tub is AT LEAST 31 KM across. Interesting idea but, my tub does not show any evidence of what we laypeople would call Coriolis effects until the depth around the drain is about 1 cm and is only really pronounced at much shallower depths. Try something like a mm and see if you get something more reasonable--I can't make out if g H is supposed to mean multiply, divide, add, or other function, and I can't tell what units f is supposed to be in. Anyways, flow like this is unsteady by definition and what may be insignificant in steady conditions may be significant in developing or unsteady flows. Adrian Pierorazio Mechanical Engineering Graduate Studies Queen's University = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Thu, 13 Apr 1995 19:31:20 -1000 From: Jay & Celine Isaacs Message-Id: Organization: RidgeNet - SLIP/PPP Internet, Ridgecrest, CA. (619) 371-3501 Subject: Re: Does water flow clockwise or counter-clockwise when going down the drain?? In article <3mj7n1$dq4@ixnews2.ix.netcom.com> Frank Kenisky, mr.nasty@ix.netcom.com writes: >>>Re; Which way does the water flow down under? Water will flow clockwise in the northern hemisphere and counter-clockwise in the southern. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Date: Sun, 16 Apr 1995 12:24:27 -1000 From: Colin_Douthwaite@equinox.gen.nz (Colin Douthwaite) Message-Id: <3ms5er$mrf@southern.co.nz> Organization: Southern InterNet Services Subject: Re: Does water flow clockwise or counter-clockwise when going down the drain?? Coreykite (coreykite@aol.com) wrote: : >Re; Which way does the water flow down under? : On my recent visit, while attempting to determine this specific question, : I was dismayed to find most toilets of the sluice-flow variety rather than : the whirling style common in the states. The question remains unresolved. : BTW, I do not bathe in tub, I am a shower kind of guy. : aoxomoxoa coreykite@aol.com Ah yes but flushing-toilet systems don't really count in these water flow experiments - however if you had put a little plastic ducky in there before flushing you could have checked which way the ducky swam around the bowl as it emptied - clockwise or anti-clockwise :-) ___________________________________ | _____ | | \ o / | | ~~~ | | Dux | | | | | | | | | ----------------------------------- | __------__ | / ./ ,....., \. \ / ./ . _ . \. \ / / >o)_// \ \ ( ( ~ (__) _ ) ) \ \. ~_~~~~~ ./ / \ \.________./ / \ / \.========./ I I I I /] [\ -cfbd- // \\ -------\\_____________//------- [ "Dux" is the trademark for a leading brand of NZ toilet ] BTW has anyone checked out which direction fighter kites spin in the northern hemisphere, if flown in the bathroom ? Bye, = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =