Is this really Coriolis effect?

1. Oct 15, 2012

quantum123

2. Oct 15, 2012

mikeph

I would suggest it is not, since they got it the wrong way around. The Coriolis force in the northern hemisphere should be counter-clockwise!

http://www.hurricane-facts.com/Hurricane-Wilma.jpg

3. Oct 15, 2012

quantum123

Why?

4. Oct 15, 2012

dipole

Seems like more of a trick to me than anything. I'm guessing it has more to do with the way that hole in the bottom is shaped.

edit: If you look closely at the video you can see he used at least two difference containers, gives more credit to my conclusion.

5. Oct 15, 2012

haruspex

It's well known that the Coriolis effect even on the scale of a bathtub in temperate zones is easily swamped by noise - details in the shape of the container, small initial movements of the fluid.
The experiment referenced was conducted within walking distance of the equator using a small dish. It would be utterly impossible to detect a Coriolis effect in those conditions.

6. Oct 15, 2012

mikeph

Because an object moving radially outwards will appear, in a rotating set of coordinates, to be under the influence of an angular force. This angular "force" will make a southerly wind in the northern hemisphere appear to accelerate westwards, and a northerly wind appear to accelerate eastwards. The opposite happens in the southern hemisphere.

The specific direction simply arises out of the mathematics.

7. Oct 15, 2012

rcgldr

In the case of weather patterns in the northern hemisphere, low pressure areas rotate counter-clockwise, high pressure areas clockwise. Wiki article has more info:

http://en.wikipedia.org/wiki/Northern_Hemisphere

8. Oct 15, 2012

mikeph

edit- got confused, give us one second

It appears it's more complicated than I first thought!

9. Oct 15, 2012

cjl

There are a number of ways in which this trick is performed, and none of them have to do with the Coriolis effect. One possibility (though it's difficult to say, since the video cuts around a bit rather than showing one continuous clip) is that some rotational motion is imparted to the water by the person holding the container - the container itself is somewhat squared off, so if you were to walk north of the equator and then turn to the right, it would impart a slight clockwise motion to the water, and walking to the south of the equator and turning a bit to the left would impart a slight counterclockwise motion. As the water drains, any initial slight disturbance will be magnified.

Also, this drain should act as a low pressure system effectively, so yes, it's going the wrong way.

10. Oct 16, 2012

D H

Staff Emeritus
It's a tourist scam. The BBC has fallen this very same scam for before in the show Pole to Pole with Michael Palin. Shame!

You can see the Coriolis effect in a pan -- a rather large pan, that is. A couple of meters across would do it for an experiment at midlevel latitudes. The Coriolis effect is so small that the pan has to be perfectly circular, rather large, and have a small central hole. How to do it the right way: Plug the hole, fill the pan with water, wait several days. You need to let the water rest for several days because the water will inevitable have a rotation just from filling the pan, even if the filling is done with great care. The Coriolis effect will be observable only if the residual rotation from filling is allowed to die out. Now pull the plug. After a minute or so you will start to see rotation build up. This is the procedure does work at midlevel latitudes such as that of MIT. This is the Shapiro experiment of 1962. There is no way this would work 20 meters from the equator. The effect is too small.

This cited video was just another tourist scam. The Coriolis effect essentially doesn't exist 20 meters from the equator. The pan used was too small for the Coriolis effect to have any effect, anywhere, let alone near the equator. Finally, the rotation is immediately observable. The trick is to pour the water into the pan so that it is rotating from the very start.