OK, so the Coriolis Force has nothing to do with the way the water drains out of a bathtub - as the BA clearly describes in Chapter 2 (Flushed with Embarrassment) of his book. It's just a myth. So if you fill, say, a dozen different bathtubs and pull the plugs on them, some will drain clockwise and some counterclockwise. Right?

Why is it then that on every occasion I have tested this hypothesis the water always drains counterclockwise?

Is it possible that there's some truth to the myth after all, only it's not the Coriolis Force that is to blame, but something else? Like magnetism.

Water is a polar compound, so the water in your bathtub has a lot of ions in it - positively charged hydrogen ions (protons) and negatively charged hydroxyl ions (OH). Presumably as these drain out of the tub they are deflected by the Earth's magnetic field - pretty much the way air molecules in depressions and anticyclones are deflected by the Coriolis Force. Could this affect the way the water drains?

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Just tested it with the kitchen sink, starts clockwise, ends up counterclockwise, strange.

What about your bathtub? Sinks are smaller, so the effect might not be the same. I was hoping to exclude them from this survey.

By the way, did you just vote: "Southern Hemisphere - Counterclockwise"? When was Finland moved to the Southern Hemisphere?

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Don't have a bathtub so I'll just exclude myself.

Eroica wrote:
Apparently I did, meant to vote other. Now I've really ruined your
survey.

Never mind. I tried to include a "None of the Above" option, but it didn't seem to come out.

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I tried my bathtub. It started counterclockwise and finished clockwise.

How many times have you tested this, Eroica?

Another urban legend sneaks it's way into the Bad Astronomy site.

It mostly just seems to flow into the drain, neither clockwise nor counterclockwise. I even tried to angle it in one direction or another, but it doesn't stay that way.

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Which way does the rubber ducky go? The two could be highly related.

Im right handed. If I'm in the tub, I swish the hot water to the back of the tub with more right hand motion than left. This initiates a clockwise motion.

If I shower, the nozzle is aimed more away from the curtain which, in my case, is to my left. This creates clockwise motion, too.

The drain pipes also are factors. Water flow has a non-uniform flow rate through a bend. A bend is, likely, just beneath your tub. This could have some effect on the flow, I think.

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Are you only doing this in one particular bathtub? The shape of the bathtub has a large influence.

For instance, when we used to model large scale fluid flow by using rotating water tables, the differences in latitude were most simply simulated by slightly sloping side to side the bottom of the table. If your bathtub is not perfectly level, that's going to induce a preferential rotation, similar to the appearance of large scale weather systems.

If you could jack up one side of your house, and repeat the experiment, that would be interesting, but you might have to play with it a little bit.

I've tested it in three different bathtubs in three different houses - all with the same result. Okay, hardly conclusive of anything. I'm just curious to see if the survey gives a fairly random spread among the various outcomes (which, I suppose, it should do).

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At least have the patience to read the OP before you comment. I don't think there are any urban legends which suggest that Earth's magnetic field could possibly influence the way water drains down a plughole (though I may have just created one! ).

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Another consideration is the plug removal. As the drain becomes unplugged, there may be a slight rotation established favoring one direction.

Can you use a pull-type plug? If so, pull from different directions.

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Well, I was referring to the old urban legend that water drains a certain way down the toilet or bath tub or sink depending on what hemisphere you live in. I thought BA dealt with this in his book and that you seemed not to believe it. However I could be wrong. I usually am.

As far as reading the post, I read it 3 times. Next time I will take notes.

I apologise if I came off a little snippy. I got the impression from your post that you were accusing me of somehow contaminating the purity of the BABB.

I was just throwing out an idea, expecting it to be quickly shot down. But no one has commented yet on a possible role for the Earth's magnetic field....

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The effect by a magnetic field is deflection in different directions for the opposite ions you talk about in the OP--since the charge below even the macro level is essentially neutral, the effect should be minimal or even non-existent, shouldn't it?

If you say so, but the hydroxyl ions are 33 times as massive as the hydrogen ions. Would that make a difference?

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I'd have to do some calculations. What is the average molecule speed in water?

African or European? :-k

Does it need to carry a coconut?

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So which way should the water go?
It seems as though it should be atomically a democratic decision.
10kg of water votes to go clockwise,
10kg+1molecule of water votes to go anti-clockwise,
(ignoring the fact that a more energetic molecule gets more votes than a less energetic molecule)

once the ball is rolling, the potential kinetic energy of the water provides the real energy(edit- for the wirlpool) as it falls through the hole...

And how ever small the difference, the molecules of water at the southern end of the bath are moving faster(west to east) than the molecules at the northern end. (edit- in the northern hemisphere anyway)

Hay presto, a democratically elected whirl pool!!!!!

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Perhaps, as it is a democracy based upon the energy level of the water molecule they could be said to be olichary wirlpools!

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I guess the neutral molecules will always greatly outnumber the ionised ones, so my idea's a nonstarter. #-o

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I thought all water molecules existed in their ionic state...
.

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The problem is, there are other effects that completely swamp that "how ever small difference"--intial rotation of the inflow, shape of the basin, tilt of the basin, minor distrubances, etc.

It's like that effect of the moon's tide on earthquakes--of course there is an effect, but it is so small, that it is just useless for predicting earthquakes.

I wonder if the gyroscopic effect has anything to do with it?
After all the Earth is just a giant gyroscope and so I suppose is the water, if taken as a single unit!!!

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It's nice to see that the results of the poll are, in fact, about what we'd expect.

You've still got very few replies...

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It is a small data sample, true. I'll admit that I haven't taken thetime to test this on my own bathtub, so I haven't voted myself. I'll have to check.

I do understand that there are folks living in countries on the equator who will "demonstrate" this effect for tourists. They take a big basin filled with water, walk across the equator to the north side, pull out the stopper, and the water circles one way. Then they refill the basin, walk to the south side of the equator, and the water circles the other way, amazingly enough. Of course, what you didn't notice, since you only saw them do this once or twice, was that after crossing the equator they always carefully turn around to face you again in the correct direction to start the water rotating the way they'd like imperceptibly. That small bit of angular momentum is all it takes to have the water spiral in either direction, provided that the basin itself is pretty uniform.