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I'm aware of the previous answer to this question. But my question is concretely about this video. Is it fake? How?

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Martin Argerami
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    The first time the water is completely still, while in the other two cases the recipient is emptied while the water is still moving. Moreover, the second time the recipient is loaded from the left side while in the third experiment the water is poured from the right. – Dr. belisarius Mar 07 '15 at 15:30
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    As the answer to the previous question noted, it is very easy to influence the outcome of a small-scale Coriolis demonstration. – Mark Mar 07 '15 at 22:03
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    Note how he puts the leaves which help you see the water movement only _after_ opening the drain. Otherwise you'd clearly see it's moving even before. – vartec Mar 12 '15 at 18:54
  • Water may not be a very good example since there are many influences besides the correole-effect. It is verified though that low pressure zones (low pressure forms as the air contains more water) move in different directions on the two hemispheres. –  Mar 13 '15 at 14:09

2 Answers2

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The video is likely fake.

Watch closely how he pours the bucket. We don't see him pour it the first time. However, the second time, he pours it into the left side of the sink (from his perspective). This causes the water to have a clockwise motion (since it flows upwards on the left side). The second time, he pours it into the right side of the sink. This causes the water to have a counterclockwise motion (since it flows upwards on the right side). It is likely that the first time, he poured it into the middle. The nature of the hoax is covered in more detail by astronomer and skeptic Dr. Phil Plait at The Bad Astronomy Blog

There is a similar trick I saw in Kenya, where they turn one way before putting a bucket down on side of the equator, turn the other way on the other side, and put it down without turning at all in the middle. Dr. Phil Plait also covers this hoax in his book, Bad Astronomy (google books link to the chapter)

Sklivvz
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TheBlackCat
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    Please [provide some references](http://meta.skeptics.stackexchange.com/q/5) to support your claims. – Oddthinking Mar 11 '15 at 23:40
  • Citations have been added. – TheBlackCat Mar 12 '15 at 07:29
  • You did not prove that the video is *certainly* fake, but you provided circumstantial evidence that it is. I've edited your answer to reflect this. – Sklivvz Mar 12 '15 at 09:42
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    I provided a reliable source that said it was definitely fake. – TheBlackCat Mar 12 '15 at 09:43
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    @TheBlackCat, I really like Phil Plait, but his is just an opinion. A stronger form of evidence would be e.g. the person in the photo explaining the trick. Being able to replicate a trick (or explaining why a behavior is what it is) does not warrant calling it a "fake", a "trick" or a "hoax". – Sklivvz Mar 12 '15 at 11:42
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    So we can't call something a trick unless the trickster admits to it? – TheBlackCat Mar 12 '15 at 12:03
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    @TheBlackCat that was an example. There are other ways, [James Randi does it all the time](http://en.wikipedia.org/wiki/One_Million_Dollar_Paranormal_Challenge). – Sklivvz Mar 12 '15 at 23:46
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    I have provided two reliable sources from an expert in a relevant field that provides multiple studies showing that the given explanation could not possibly be correct and explains in detail why this could not be anything other than an intentional hoax. You have added what, by wikipedia standards, would be "weasel words", but have provided no sources that cast any doubt on my source. This would seem to me to be a clear case of original research on your part, which, as Oddthinking pointed out, is not allowed. – TheBlackCat Mar 13 '15 at 08:22
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    @Sklivvz can you give an example where Randi shows something is a trick *afterwards* without just demonstrating how it was done? –  Mar 13 '15 at 15:27
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    This page (http://www.dvandom.com/coriolis/sink.html) provides a calculation that indicates that coriolis cannot explain the rotation in a sink. This paper (http://www.nature.com/nature/journal/v207/n5001/abs/2071084a0.html) also suggests that the effect is too small (I think it is the study that Plait refers to). Note corolis effect will be weaker at the equator than anywhere else as that is where the earth is best locally approximated by a cylinder, so the effect will be smaller there than in the experiments in the paper. –  Mar 13 '15 at 17:08
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    @TheBlackCat expert opinions are appeals to authority. [Here's what Oddthinking has to say about those](http://meta.skeptics.stackexchange.com/questions/2697/should-a-person-who-is-more-qualified-be-subject-of-less-skepticism-than-one-who/2699#2699) – Sklivvz Mar 13 '15 at 17:35
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    And if I based what I said solely on his authority then you would have a point. I didn't, though, I based what I said on his authority, his evidence, and his arguments. To oppose this, you have provided nothing but an incorrect claim that he was just providing an opinion (he didn't, he provided evidence and arguments for his conclusions). You have provided no authority, no argument, and no evidence. Unless you can do so, your addition of weasel words is original research, which is not allowed. You haven't even provided a feasible standard that would satisfy you. – TheBlackCat Mar 13 '15 at 18:19
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    Plait's book gives more than opinions, there is also an explanation of the coriolis effect and some calculations (sadly I can't see all of them on google books, but what is there shows it to me more than just opinion). Oddthinking says "Humans have limited mental budgets for establishing the truth of each claim.", I certainly agree with this, and after noting that physics show that the effect on that scale is essentially zero (esp. near equator), and observing that the water is circulating **prior** to the plug being pulled, and that the water was poured in on different sides, ... –  Mar 13 '15 at 19:52
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    ... most people would conclude that a sufficient amount of mental budget has already been expended. In science showing how a result can be incorrectly obtained and that the purported explanation cannot give rise to the observed strength of effect *is* considered sufficient to refute the claim, with no need for a reference. –  Mar 13 '15 at 19:54
  • And with this, you both completely failed to convince me that the evidence gives us *certainty*. We're debating an adverb... There can be better evidence therefore there can't be certainty. Btw my mental budget is now extinguished. – Sklivvz Mar 14 '15 at 11:11
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    There can always be better evidence. There is no such thing as certainty in science. Even confessions cab be false. If that is your standard, then we would need qualifiers in front of everything. It is a fundamentally impossible standard, as many skeptics, James Randi included, have spent considerable time explaining. – TheBlackCat Mar 14 '15 at 11:31
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    If a journal paper published in Nature does not convince, one wonders what would. The paper in question shows that the effect of the Coriolis force at this scale is so small that it is barely demonstrable in very carefully controlled conditions (almost all of which are violated in the video), and performed at a latitude where the Coriolis effect will be much stronger than near the equator. This shows that the rotation of the earth physically cannot be the explanation of what was observed, which means that it must be a trick (including the possibility that the person was fooling themselves). –  Mar 14 '15 at 13:57
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    By the way the point made by @TheBlackCat about there being no such thing as certainty in science is made rather beautifully by the final paragraph of Trefethen et al. (the nature paper I linked earlier). Anybody interested in the philosophy of science or scientific skepticism would do well to read it. –  Mar 14 '15 at 15:05
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While TheBlackCat's answer (+1) is fully sufficient, this letter that appeared in Nature describes the authors experiments which show that (in Boston) if you set up the experiment very carefully, you can show that the Coriolis force reliably dictates the direction in which water drains from a basin specifically designed to negate other influences (see also southern hemisphere replication in this Nature letter). However, the rotation was only counterclockwise if you let the water settle for 24 hours and only started 12-15 minutes after opening the drain. The interesting fact is that the letter concludes:

"Incidentally, those who claim to have seen the direction of swirl change as a ship crosses the equator are surely pressing the case too far. At the equator the Coriolis forces vanish, and it would be virtually impossible to perform a valid experiment a short distance from the equator" [emphasis mine]

The Coriolis acceleration is proportional to the sine of the latitude (see e.g. wikipedia) so the last place on Earth the direction of draining would be dictated by the Coriolis force would be a couple of meters from the Equator.

So yes, we can be certain that the demonstration in the video is a trick, in the sense that it is not a legitimate demonstration that the direction of the vortex is governed by the rotation of the earth. The Coriolis effect is way too small to have created a vortex of that speed that quickly, and also the effect vanishes as you approach the equator anyway! The effect in this case is almost certainly due to the fact that the water is poured into the basin from the side that produces the desired vortex direction. This is something that was dealt with in the properly performed experiment by pouring the water into the vessel to create an initial rotation in the wrong direction, that would have to be overcome by the Coriolis force.