Water down a Plughole?

[Richie Stan]

Its that old chestnut. What does happen to water down a plug hold at the equator, clockwise or anticlockwise?

[heathfield]

It just drains straight down, and doesn't rotate! There's a local guy who demonstrates this to tourists in Kenya with a ptastic bowlful of water with some bits of grass floating in it. Even 20 yards from the equator, the water rotates, but on the exact spot, it doesn't.

[Richie Stan]

20 yards must be far too small a distance for the effect to change. What has changed in this short distance? You are no closer to the central axis of the earth.

I suspect the water is pored in at an angle, or a slight moving of the bucket to rotate the water, it would only need to be started and rotation would continue.

[boobesque]

of course 20 yards would move you away from the central axis of the earths spin. the central axis could be a centimetre wide. 20 yards wouldnt make much difference i agree but there would deffinately be some small difference

[Richie Stan]

Ive read it a myth, and that the direction is due to the shape of the container or the rotation of the water pored in.

http://www.weatherimagery.com/myths_coriolis.p hp

Paragraph four...

[heathfield]

It really happens, Richie, and if there were any cheating, I'm sure some sharp-eyed tourist would spot it. The basin is filled, the water settles, and some grass is sprinkled in. There's a small (maybe 1/4") hole in the centre of the base plugged with a piece of wooden dowel that protrudes above the water. When the dowel is removed, the water begins to drain, and then slowly it starts to rotate. Any trickery would be obvious from movement of the floating leaves of grass. Strange, but true!

[Richie Stan]

http://itotd.com/articles/498/the-coriolis-for ce/

http://www.abc.net.au/catalyst/stories/s160444 4.htm

These sites beg to differ.

[heathfield]

Just read your links, Richie, and there are several more like them on the web. I agree that the shape of the vessel and its drainage system may have most effect on the direction of rotation.
But... Strangely, there have been only two rigorously scientific experiments reported that researched the phenomenon. One was by a physicist, A.H. Shapiro, at Mississippi Technology Institute in 1962, and the other by a team at Sydney University in 1965.
Both experiments confirmed the effect.
Reading the ifs and buts in the last paragraph on your 'itotd' link, the writer actually admits the possibility!
The last link merely supports what I say about the vessel and drainage design.

[Richie Stan]

But you could concede that the demonstration in Kenya is not a scientific experiment and could just as well be performed in Egypt on the Tropic of cancer. Using the same bowls, as it will be the shape of the bowls and the movement of the water after filling that greatly effects the direction of rotation?

[Richie Stan]

I myself, after read up, concede that given perfect environment the rotation will be different, north or south of the equator, but these perfect environments are never replicated in real life.

Therefore the idea that as a rule the water rotates counter-clockwise in the north and clockwise in the south is false.

[ugly_bob]

but it's been demonstrated in yellow glory in the American Embassy in Oz

[fo3nix]

It doesn't depend where the plug hole is on the planet. Sometimes it'll rotate clockwise, sometimes anticlockwise, and sometimes it'll just pour straight down. It just depends on the shape of the sink and plug hole, as well as the way you pour it.

[dawkins]

http://www.snopes.com/science/coriolis.htm

its a myth fellas, and fellasses.

[Gef]

dawkins is correct. I'm just back in Glasgow after 5 weeks in New Zealand and you can influence the water to go either way.

[boobesque]

why did you post this question richie stan?

[Richie Stan]

It�s just one of those things that a mate and I at work talk about during the night.

I thought at first that it would never flow straight down as only a slight rotation would accelerate to a noticeable one, like water on a ball will always flow down one side more than another.

Thanks all though I think the myth is truly busted.

[gslusher]

Heathfield wrote: " One was by a physicist, A.H. Shapiro, at Mississippi Technology Institute in 1962 ... ."

Right name, wrong discipline and wrong university. Ascher Shapiro was a professor of mechancial engineering at the Massachusetts Institute of Technology (MIT). It's a long way from Mississippi. Cambridge, Massachusetts, where MIT sits, is 1139 miles from Oxford, Mississippi, the home of "Ole Miss" (the University of Mississippi). That's almost the distance between London and Minsk, Belarus.

When I got to MIT in 1965, Professor Shapiro was head of the Mechanical Engineering Department.