Today’s Blue Peter on CBBC managed to resuscitate a long-standing myth for a new generation of viewers.
A segment of the programme showed presenter Konnie Huq on a trip to the equator in Uganda where she was shown a purported demonstration that water in the northern hemisphere flows out of a basin with a clockwise rotation, in the southern hemisphere the rotation is anticlockwise, while on the equator itself, the water flows straight out of the basin with no rotation at all. In fact, this is a trick performed by mountebanks at tourist spots across the equator in order to drum up trade.
The supposed phenomenon is said to occur because of the superimposition of motion on the rotation of the Earth. It’s called the Coriolis effect. The effect itself is real and can be seen in storm formation in both northern and southern hemispheres, but the rotational force exerted is far too small to have an effect in a short timescale on a small basin of water anywhere on Earth, let alone one placed so close to the equator. The Coriolis force is easily swamped by the tiniest currents in the water, which accomplished fakers can induce in the basin by small movements of the apparatus on the pretext of giving the audience a better view.
Fuller explanations of this fake phenomenon can be found here and here. The second of these links shows a transcript of a conversation between Michael Palin and a Kenyan “demonstrator” on a programme in the “Pole to Pole with Michael Palin” series. So this is not the first time this has happened to a reputable broadcaster – though since in both cases the broadcaster was the BBC it may be the first time a reputable broadcaster has been fooled twice by the same well-known trick.
Edit
Having just checked my sources, I now find that the Coriolis effect causes anticlockwise motion in the northern hemisphere and clockwise motion in the southern. Looks like the charlatans can’t even be bothered to get their facts straight!
October 3, 2008 at 5:03 am |
Like you, I have a web-log but unlike you, I’m a beginner having just started on August 24, 2008. I’m a retired meteorology and geology professor who does only a limited amount of teaching these days and I find that the web-log provides a wonderful outlet for my continuing desire to teach and learn. Moments ago I posted the first installment of a discussion of the Coriolis effect as it relates to earth systems. Within moments of my posting a “Possibly related post” provided a link to your piece, “Coriolis effect sends Blue Peter into a spin.” I enjoyed reading it.
A professor at the U.S.A. college where I taught and learned for many years came home from Kenya after an exciting vacation with a video tape of one of those parlor tricks performed in a village on the equator. Even today, I’m not sure he believes that he was duped. I’ve heard that similar “demonstrations” are performed aboard cruise ships when crossing the equator.
I read your editorial comment: “Having just checked my sources, I now find that the Coriolis effect causes anticlockwise motion in the northern hemisphere and clockwise motion in the southern. Looks like the charlatans can’t even be bothered to get their facts straight!”
In fact, the Coriolis effect causes both clockwise and counter-clockwise rotation in the northern hemisphere and the same can be said for the southern hemisphere!
In the northern hemisphere mappable-scale cyclones (rotating lows) rotate counter-clockwise and mappable-scale anticyclones (rotating highs) rotate clockwise.
In the southern hemisphere mappable-scale cyclones rotate clockwise, and mappable-scale anticyclones rotate counter-clockwise.
By mappable-scale I mean those systems which are large enough to appear on a weather map which shows weather systems the size of air masses, hurricanes, fronts, etc. The distinction is made because there are cyclones (rotating lows) of a much smaller scale that can rotate either way in either hemisphere. An example would be a tornado. Even then, the majority comply with the Coriolis rule of the particular hemisphere in which it develops. Another example is a category of thunderstorm (cumulonimbus) which is rotating. Like a tornado, it is too small to appear on a mappable-scale plot. These thunderstorms are often referred to as mesocyclones or mesocyclonic storms.
I look forward to exploring your web-log. It looks interesting. I’m at cloudman23.wordpress.com