Thursday, July 29, 2010



My name is Michael Sullivan. I'm an employee at BU and I'm also a part-time student finishing up an undergraduate degree in Computer Science -- if all goes well this will be the last class I have to take. I work as a system administrator in a group called BUworks, which is a temporary department set up to do a software implementation and replace BU's central HR and financial software. I was born in Virginia but only lived there for a couple of months, and I was raised in a number of places up and down the East Coast -- we moved every few years because my father was in the US Navy. Luckily for me, the Navy keeps most of their stuff near the ocean, so I've never lived without easy access to the beach. Most of my childhood was spent in Rhode Island or North Carolina.

I needed one more course for my degree and this one looked perfect. It's short, it's a good excuse to take a week off of work, it's all field trips, science is awesome, I love being on and around the water, and I enjoy observing nature and thinking about how and why things are the way they are. This should be fun.

So, on Monday we saw two things in the ladies' room. First the professor covered the drain with his hand, filled it up, and let it empty out. As the sink emptied a whirlpool could be observed briefly, spinning counterclockwise. We then moved to the toilets and flushed them, observing the flow of water. In the toilet the water drained in a clockwise direction. The flow of water in the toilet was dominated by a large jet of fresh water draining from the tank into the bowl, which probably makes it a poor candidate for comparison to either the sink or an Australian toilet.

The reason draining bodies of water are supposed to flow in opposite directions in different hemispheres is presumably the Coriolis effect, which does twist large storms and the like in opposite directions. However, my understanding of the Coriolis effect, from previous classes and readings, is that it is caused by the different speeds of the Earth's rotation in different locations. This difference is itself related to the changing diameter of the Earth as you move towards or away from the equator. The difference in the Earth's diameter between one side of the sink and the other is negligible, so the resulting force is unlikely to play a role in determining how the water drains.

A check against Snopes seems to confirm this ( and they state that the shape of the basin and its level are probably the most important factors.

There are a number of potential reasons the other half of the class might have observed the sink draining in the opposite direction -- they (or we) might have seen it wrong, or the professor might have used a different sink with different imperfections in its shape. Professor Berman probably lifted his hand through the water in a slightly different fashion, imparting some initial direction to the water's movement that was amplified as it drained. It is unlikely he would be able to exactly reproduce the motion both times.

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