Upon hearing a travel report from an acquaintance spending time this summer in Ecuador, I could not resist asking her to observe which way her sink and toilet drained. I’d heard that, due to the Coriolis effect, when you flush water in the northern hemisphere it swirls one way (clockwise), but below the equator it goes the opposite way.* Here is her enthusiastic report:
“Hi Mark, Yesterday I tested it – it´s true! We went to the Mitad del Mundo (Centre of the World), a big monument where the equator line is supposed to be. Unfortunately, they made a mistake when measuring, so the real equator line is a five minute walk away from the monument. By the real line they built a museum and there you can do funny experiments. For example, they put a sink on one side of the equator and let the water flush down, and then they move it to the other side and the water flushes the other way. On the line itself the water just goes straight down – no kidding! It was very interesting!”
I then had to do some research to see if this phenomenon could be independently verified. I hate to be a party pooper (ha, ha!), but, from what I read, in reality the Coriolis effect is so small that it’s easily overwhelmed the shape of the bowl and the other factors. Thus, most toilets flush in only one direction — clockwise or counterclockwise — regardless of location. This is explained very nicely by Alistair B. Fraser, Emeritus Professor of Meteorology Pennsylvania State University, in his white paper on Bad Coriolis.
In any case, it is fascinating to watch the last gallon of water from a hot bath twirl down the drain, so why not observe whether it exits clockwise or counter? I’ve never been south of the equator myself – the nearest I came was in Singapore. My hope is to do some personal validation on the Coriolis effect, or lack thereof. Why not?
*In a memorable episode (I thought it extremely funny) of the television cartoon The Simpsons (16th one in the 6th season), Bart, purporting to be an official with the “International Drainage Commission,” convinces an Australian boy to do a similar ‘down-under’ experiment. The results proved inconclusive, but very humorous. 🙂