Even if this did work at the equator, local gravity differences would cause the line going around the world to we wiggly, i think.

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Is that some sort of UTI?

I just did the bathtub test. The plug is built-in. To drain the tub, I have to turn it counter-clockwise. The water drained counter-clockwise, too.

Ah ha! (Sorry it took this long to see your comment.)

Does anyone remember the BA's book section discussing the fraud at the equator? AS he changes hemispheres, he turns the direction needed to initiate the desired rotation direction in the water.

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of course if you rotate the water one way then that is the way it will spin when it drains but that doesn't mean that if the water is perfectly still before it drains that it won't spin anti-clockwise in the northen hemisphere.....

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True, but why. The direction is caused by some force. It is likely due to one, or more, of the following...

1) The water has a net rotation direction prior to draining.
2) The drain plug removal forces a rotation direction.
3) The drain itself creates a rotation due to the non-perfect plumbing.

I can't think of anything else. I am intentionally leaving out the differential spin rate due to Earth's rotation and any electromagnetic possibilites.

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Those sound pretty good. I'd also add a lack of symmetry in the bathtub itself that might provide a preferential direction as the water drains.

In the science museum in London there is a 30ft(guess) pendulum suspend from a high ceiling, it is free to swing anyway it wants but as the day goes by its swing changes direction, due to the rotation of the Earth(this is the point of the demonstration). So if a small weight can keep its momentum relative to the Earth's revolution then why couldn't the water in a bucket? The amount of energy in the water in a bucket treating it like a fly wheel is 0.0000....1 (I've for forgotten how many zeros) joules but it may be enough to tip the balance in a still bucket of water.
Once the water is spiraling the actual energy for the whirl pool comes from the falling of the water through the hole...

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I calculate that water in a sink has 0.0000000046 joules of water due to the rotation of the Earth and if that was concentrated into 1 cubic centimeter of water, then that cubic centimeter could travel at 1.5mm a second. Maybe enough to get the whirlpool show on the road. I'm not sure about the mechanism for turning the gravitational potential energy into kinetic energy(as the water falls through the hole) but this would have to be considered even when pre-swirling the water anyway.

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4) Asymmetric bathtub.

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Is the pendulum in a vacuum? It is very difficult to make them work right due to air currents, swivel friction, etc. I know of a 30 or 40 footer that was abandoned.

Sounds right. It should take little to get one started, but once started it is self-supporting if it doesn't roam around.

Is the 1.5mm/sec the differential rate from one end of the tub to the other? In the area near the drain, I would expect less of a differential rate calculation.

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No, the 1.5mm/sec is just if the energy was concentrated into 1 cubic centimeter of water(it's quite a small amount of energy). But the actual volume of the water involved in the whirlpool is probably quite small, just a few mm in from the surface(at the start), I would have thought.
If (for example) one centimeter of water has gone down the plughole then all that angular momentum in that top layer will have had to have gone somewhere.

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ps. the pendulum(I just googled it and found that it is called a Faucult pendulum) in London is just in the open air IIRC.

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My water drains down.

CJSF

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Two years ago moved from my town
I was looking up past the city lights
But the city lights got in my way

See the constellation ride across the sky
No cigar, no lady on his arm
Just a guy made of dots and lines

-from "See The Constellation"
by They Might Be Giants

Across a 15cm diameter at the drain, I get about 2 mm per minute as the differential rate of rotation around the center of the earth. The idea the Coriolis effect causes drain rotation seems to...uh...go "down the drain".

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Surely, all things being equal, even a small rotation in a round container will lead to a whirlpool in the same direction, although not at or near the equator, that is just a con(although I used to believe it).

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I did this experiment with a sink at work...

I found that it drained in whichever way I stirred the water; I had to do that to overcome the swirling motion caused by the asymmetric position of the tap relative to the sink's c.o.g. At no point did it reverse so as to conform to the mythology!

there is noway that the initial energy of the system could overcome the active swirling of the water, that would put far to much artificial energy into the system.

Active swirling doesn't disprove the phenomenon. You have to perform the experiment with still water in a round bucket with a hole in the middle. And not at the equator, where the water is revolving perpendicular to the plane of any resulting whirlpool. After all when they dropped objects of the tower of Pisa they didn't use a hammer and a feather.

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mine just goes straght down, until the end where a funnell opens.

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Pendulums are smple to make. However, good luck making it work.

Foucault discovered it by serendipity. He built one in a Paris church (the Pantheon). His was 67 meters tall. The higher the better.

There appears to be one working at the University of Sydney... here . I saw another site showing it working in 1999. It would be interesting to know how many are actually operatonal.

It demonstrates inertia from which shows the rotation of the Earth. You can accurately calculate g from these and the rotation rate of the Earth. It does not demonstrate the Coriolis effect.

ops: . I missed it horribly. I believe it is 1e-15 mm/hr. (10 cm diameter). This is at the equator. (2xpi/24)x(1- cos(arctan(.333/(4000x5280)))) ft/hr.

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I don't know if the Coriolis effect is the same as treating the water in a bowl of water as a flywheel?

The effect should be greatest at either of the poles and nonexistant at the equator.

I remember hearing a saying once, "a penny a year profit=happiness, a penny a year loss=misery", surely any amount of rotation in one direction(in a still bowel of water) will cause the whirl pool to opt for the same direction(anticlockwise in the northern hemisphere).

The shape of a bath or sink shouldn't matter as long as the container is symmetrical.

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Here's the issue. No bowl of water is entirely still, there will always be some random motion or residual motion from filling the bowl. Moreover, there may be asymmetrical effects from the way the drain is configured or other such issues. If the Coriolis effect is sufficiently small (which it is for a small container of water), it will be overwhelmed by these effects, so there won't be a preferential direction based on hemisphere. As you can see by the (admittedly small) poll sample here.

Quite true. At 60 deg lattitude, the differential rate across 4 inches is about 1 inch per hour (hopefully my rushed math is right). Significantly higher, yet still insifnificant in it's effect on the rotation direction and rate.

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Down. Very slowly. I need to clean the drain...

(Northern Hemisphere, 40-mumble degrees)

I wonder has anyone tried the same bathtub in each hemisphere! If the water drained the same way both times, Coriolis's goose would be well and truly cooked.

Australian Custom Officer: Anything to declare, sir?
Eroica: Er, just a bathtub ... oh, and my genius!

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I can ship a bathtub via company mail (on United only) from ORD to an airport we fly into (must be a true United flight).

Take the kitchen sink instead.

How 'bout using a round bucket, install a drain/plug and using a large hose to simulate the pipe works. Try different hose arrangements to see what influence this has on the rotation direction.

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Counter-Clockwise

Clockwise down here.