[user123]

Hi,

I'm having some questions about this effect.

Please watch the full video below to understand, video starts at 30s:



In the video you can see that this effect only happens when the earth is rotating and the poles oppose eachother.
It's required that the poles oppose eachother, otherwise there won't be a difference where you are on earth. Water would just move faster when you are at the edge.

How would such effect be possible if the earth is another shape than a globe (or globe like shape)?

[Pete Svarrior]

This is a common urban myth, mostly perpetuated by tourist traps around the Equator. This effect does not occur in reality, even if you choose to believe that the Earth is round.

I appreciate Veritasium's attempt at challenging mainstream science through experimentation, it's an approach I'm very fond of. However, they failed to account for factors like the shape of the pool and the hole within - neither are perfect cylinders, and this will have a greater impact on the direction than any supposed Coriolis effect. The same goes for trade wind patterns affecting both hemiplanes/hemispheres (i.e. the actual cause of cyclonic motions).

Two articles for your attention, written from a RE perspective:

• https://blog.drwile.com/once-again-dont-believe-facebook-when-it-comes-to-science/
• https://www.americanscientist.org/blog/science-culture/the-coriolis-and-the-commode

And a couple of FE articles on the "Coriolis effect":

• https://wiki.tfes.org/Coriolis_Effect
• https://wiki.tfes.org/Coriolis_Effect_(Weather)

Hopefully this helps.

[JSS]

That's a great video. There have also been many controlled, scientific experiments as well.

https://www.technologyreview.com/2012/10/24/183079/verifying-a-vortex/

The first experiment was done in 1962 by Ascher Shapiro where he was careful to document and control for other influences. Temperature and air currents were among the variables he accounted for.

He also used a plug, filled the pool in the opposite direction of the expected rotation, let it sit for 24 hours. Clearly the video makers used his experiment as a basis for theirs.

Shapiro found that water did indeed rotate consistently in the direction predicted, and another experiment in the southern hemisphere showed the opposite effect. After his paper was published, numerous scientists performed their own experiments which confirmed his results. Lucky for us, it was a popular experiment for a while so there was a lot of separate experiments all around the world to confirm it.

After checking the TFES Wiki I see it references the same magazine article I found and highlights the difficulties in performing such experiments.

Two of the studies were published in Nature, one for the northern hemisphere and one for the southern.

Bath-Tub Vortex, Ascher H. Shapiro, Nature 196, 1080-1081

The Bath-Tub Vortex in the Southern Hemisphere, Lloyd M. Trefethen, R. W. Bilger, P. T. Fink, R. E. Luxton & R. I. Tanner, Nature 207, 1084-1085.

There was a similar experiment that also verified the Coriolis effect in water draining that was conducted way back in 1908 by O. Turmlïtz.

https://www.nature.com/articles/197480a0

Bathtub draining is a pretty well researched area of science it seems.

[iamcpc]

I appreciate Veritasium's attempt at challenging mainstream science through experimentation, it's an approach I'm very fond of. However, they failed to account for factors like the shape of the pool and the hole within - neither are perfect cylinders, and this will have a greater impact on the direction than any supposed Coriolis effect. The same goes for trade wind patterns affecting both hemiplanes/hemispheres (i.e. the actual cause of cyclonic motions).

I agree. In addition one pool was indoors and one was outdoors. If they did this experiment with the same pool, same tubes, both indoors, same altitude, same humidity, same temperature then switched positions relative to the equator and did the same experiment again it would dramatically strengthen the results as evidence.

As is this evidence is not overpowering.

[JSS]

I appreciate Veritasium's attempt at challenging mainstream science through experimentation, it's an approach I'm very fond of. However, they failed to account for factors like the shape of the pool and the hole within - neither are perfect cylinders, and this will have a greater impact on the direction than any supposed Coriolis effect. The same goes for trade wind patterns affecting both hemiplanes/hemispheres (i.e. the actual cause of cyclonic motions).

I agree. In addition one pool was indoors and one was outdoors. If they did this experiment with the same pool, same tubes, both indoors, same altitude, same humidity, same temperature then switched positions relative to the equator and did the same experiment again it would dramatically strengthen the results as evidence.

As is this evidence is not overpowering.

The experiments I referenced in my post above did take more factors into account and with much more care than the YouTube video.

I finally found the actual text of the 1962 paper, along with his offer to provide detailed descriptions of all his methods and equipment for the experiment so others could replicate the experiment in the southern hemisphere, as did many, one such was included in my reply above.

Here is the full text of the paper.

https://www.math.fsu.edu/~moore/SeminarFiles/BathtubVortex62.pdf

Of course, this doesn't prove the Earth's rotation, no single experiment can do that. But with all the many experiments having been done with such care, the evidence is indeed overpowering that water drains one direction in the north and the opposite direction in the south.

[Tom Bishop]

Shapiro's results were disputed.

From p.47 of Flow: Nature's patterns: a tapestry in three parts by Dr. Phillip Ball:

“ A popular notion says that the rotation of the earth starts the bathtub vortex spinning. But while it is certainly true that this rotation controls the direction of the giant atmospheric vortices of cyclones, which rotate counter-clockwise in the Northern Hemisphere and clockwise in the Southern, the influence of the Earth’s rotation on a micro-cyclone in the bath should be extremely weak. Biesel claimed that it cannot be responsible for the bathtub vortex because, contrary to popular belief, they may rotate in either direction at any place on the planet. But is that really so? In 1962 the American engineer Ascher Shapiro at the Massachusetts Institute of Technology claimed that he had consistently produced counter-clockwise vortices in his lab by first allowing the water to settle for 24 hours, dissipating any residual rotational motion, before pulling the plug. The claim sparked controversy: later researchers said that the experiment was extremely sensitive to the precise conditions in which it was conducted. The dispute has never quite been resolved. We do know, however, why a small initial rotation of the liquid develops into a robust vortex. This is due to the movement of the water as it converges on the outlet. In theory this convergence can be completely symmetrical: water moves inwards to the plughole from all directions. But the slightest departure from that symmetrical situation, which could happen at random, may be amplified because of the way fluidflow operates. ”

[JSS]

Shapiro's results were disputed.

From p.47 of Flow, Nature's Patterns, a Tapestry in Three Parts by Dr. Phillip Ball:

“ A popular notion says that the rotation of the earth starts the bathtub vortex spinning. But while it is certainly true that this rotation controls the direction of the giant atmospheric vortices of cyclones, which rotate counter-clockwise in the Northern Hemisphere and clockwise in the Southern, the influence of the Earth’s rotation on a micro-cyclone in the bath should be extremely weak. Biesel claimed that it cannot be responsible for the bathtub vortex because, contrary to popular belief, they may rotate in either direction at any place on the planet. But is that really so? In 1962 the American engineer Ascher Shapiro at the Massachusetts Institute of Technology claimed that he had consistently produced counter-clockwise vortices in his lab by first allowing the water to settle for 24 hours, dissipating any residual rotational motion, before pulling the plug. The claim sparked controversy: later researchers said that the experiment was extremely sensitive to the precise conditions in which it was conducted. The dispute has never quite been resolved. We do know, however, why a small initial rotation of the liquid develops into a robust vortex. This is due to the movement of the water as it converges on the outlet. In theory this convergence can be completely symmetrical: water moves inwards to the plughole from all directions. But the slightest departure from that symmetrical situation, which could happen at random, may be amplified because of the way fluidflow operates. ”

That is an opposing viewpoint, but it's from a mass market book, not a scientific publication and he did no experiments himself.

From the significant number of actual studies that did show a rotation and in the direction expected, I can't agree with his assessment that it has never been resolved.

If there was truly a controversy, there would be an equal number of studies showing that the north/south hemisphere flows don't happen, but this is not the case. The published studies all confirm it.

Nobody is denying that such experiments are extremely sensitive to initial conditions, which is why they were repeated and such care was taken to minimize any other influence introduced by the physical apparatus of the experiment itself.

More importantly, the quote you used from his book shows that he isn't claiming the Earth doesn't spin, he's just not convinced this experiment is capable of showing it. He clearly states that the Earth spins and that the Coriolis force is real and does affect the weather.

"A popular notion says that the rotation of the earth starts the bathtub vortex spinning. But while it is certainly true that this rotation controls the direction of the giant atmospheric vortices of cyclones, which rotate counter-clockwise in the Northern Hemisphere and clockwise in the Southern, the influence of the Earth's rotation on a micro-cyclone in the bath should be extremely weak."

[Tom Bishop]

but it's from a mass market book

A physicist wrote the book - https://philipball.co.uk/bio

I can't agree with his assessment that it has never been resolved.

Funny, but Dr. Phillip Ball was an editor of Nature for many years. I think he would know better than you about whether the matter was resolved or not.

More importantly, the quote you used from his book shows that he isn't claiming the Earth doesn't spin, he's just not convinced this experiment is capable of showing it. He clearly states that the Earth spins and that the Coriolis force is real and does affect the weather.

Yet the topic was water drain experiments. I see that you are attempting to move the goal post when in a weak position, unable to defend your initial claim that the Coriolis has been confirmed in laboratory water drain experiments.

[JSS]

but it's from a mass market book

A physicist wrote the book - https://philipball.co.uk/bio

I can't agree with his assessment that it has never been resolved.

Funny, but Dr. Phillip Ball was an editor of Nature for many years. I think he would know better than you about whether the matter was resolved or not.

More importantly, the quote you used from his book shows that he isn't claiming the Earth doesn't spin, he's just not convinced this experiment is capable of showing it. He clearly states that the Earth spins and that the Coriolis force is real and does affect the weather.

Yet the topic was water drain experiments. I see that you are attempting to move the goal post when in a weak position, unable to defend your initial claim that the Coriolis has been confirmed in laboratory water drain experiments.

In my opinion, several published, peer reviewed positive results by many different physicist outweigh one opinion expressed in one mainstream book, even if written by another physicist. You have raised an interesting point with his comment, but since he has not conducted any experiments of his own, it shouldn't hold more weight than the many published experimental results that do show the effect.

I don't see it as pushing the goalposts or being off topic. You introduced the quote to counter the experimental results I listed. I was pointing out that he wasn't claiming that the Coriolis force doesn't exist or can't affect physical systems, he was simply saying he didn't think that particular experiment was sensitive enough. He accepts the Coriolis force as real, his only objection was that experiment wasn't sensitive enough. It's simply not as strong as a counterexample as is claimed.

There is certainly some controversy over these experiments, but they are far from a weak position simply because one physicist thinks they were not sensitive enough, as many others concluded that they are. There are also no experiments that disprove their results after all, none that I am aware of and I have looked. But there is no subject in the world that has unanimous support.

I personally would like to see some swimming pool sized experiments, but the expense and time and effort is likely too much to solve what is a pretty minor dispute - how big of a body of water does it take to show the Coriolis force. None of the references listed here dispute that we wouldn't find it with a large enough experiment.

[Bikini Polaris]

In the wiki I cannot find the supposed behavior of draining water in FE. Is it possible that in a (impossibly) perfectly symmetric sink there would not be any vortex in FE? Are there effects, like celestial gravity or some underground vibration acting as tie breakers in that case? I'm asking from the modelling perspective.

[AATW]

while it is certainly true that this rotation controls the direction of the giant atmospheric vortices of cyclones, which rotate counter-clockwise in the Northern Hemisphere and clockwise in the Southern, the influence of the Earth’s rotation on a micro-cyclone in the bath should be extremely weak.

I find it very strange the way you cherry pick like this.

The Coriolis effect is very weak and on small scales can be hard to detect. The "fact" we all learned at school about the way toilets flush or basins drain in the different hemispheres isn't true. But that isn't a point for FE - or RE. The fact that the Coriolis effect exists and has macroscopic effects which change direction in the different hemispheres is better explained on a spinning globe earth though.

What I find weird is how you quote someone to back the weakness of the Coriolis effect up, declare him an authority - which I agree he is - but you even quote the bit where he talks about the earth being a rotating sphere. So you regard him as an expert about the thing where he's making the point you want to make, but presumably he's a know-nothing dunderhead when he talks about the earth being a rotating sphere?

The way you cherry pick which bits of science to believe in and which experts to believe is really mystifying. Often, as you do here, you quote an expert to back up a point but disregard that the expert is also confirming the globe earth. Do you really not see how disingenuous this is?


As for the experiments being discussed. Personally I think they did a pretty good job at trying to eliminate external factors but the results either way aren't a point for either side.