World

12/06/2009

The Equator Myth: Coriolis

People say that water draining out of a bath or flushing down a toilet swirls in a different direction, depending on which side of the Equator you’re on. Is this true? 

In 1998 I went to Uganda, south of Fort Portal and Kasese. Here is a picture of the monument marking the equator alongside the road. It's not hard to find, since there are only two major roads crossing the equator in Uganda.
I was packed with water, a funnel and a few bottles, and I was ready to see if the rumors were true. I tried pouring the water a hundred times, both north and south of the Equator. I could see clearly that the water went through very fast, but not that it ran in different directions. It was very hot out there, and with every trial I spilled some of the water. I had to try hard not to drink it. 

I always thought I had done something wrong, but then the Internet came along, and I found that there are many other people who also doubt this myth. "The idea that water goes in different directions down the plughole in the Northern and Southern hemispheres is almost entirely a myth. The Coriolis effect on the Earth is very, very small, becoming apparent only in large, slow systems like the rotation of the atmosphere," says Steve Bowers in speculative science in the Guardian


Andrew from Plymouth comments,  "I have been a seafarer for over 30 years and have crossed the Equator many times, North to South and vice versa." Never has the direction of the vortex of water in a basin been a subject of discussion. If it were true, surely seamen would have spent many hours observing and then talking about this myth.



My next trip for this project will be to Macapa, Brasil. I want to go to Estadio Milton Correo, where there is a football pitch right on the equator. It actually divides the pitch in two, so if the team chooses sides (after the toss) they are also choosing hemispheres. Here you can see an image inside the stadium. Look carefully at the front of the field: "SO" and "NO" are written in the grass.