Tuesday, June 30, 2009

Guest Post: Coriolis Fail

This is a guest post by astropixie, one of our intrepid SPS interns, who contributes to the educational physics site Physics To Go

When I was sixteen, I visited Australia. The first thing I did once I checked into the hotel was fill up the sink in the bathroom, throw a gum wrapper on the surface, and drain the water, watching to see which direction the wrapper would spiral downward. If it went counter-clockwise, everything I learned from public school and television would be vindicated. If not, I intended to blame the shape of the sink and continue to live in my fantasy world—a world where the turn of the Earth affects the water in my sink but curiously disregards almost everything else in my daily life.

Those familiar with the Coriolis force will know that I was a moron in high school (and can rightfully wonder what I am doing writing for a physics blog today). But it is not my fault. For some reason, my eighth grade science teacher told us with certainty that this experiment was trustworthy and repeatable. As we huddled around the sink and watched the water swirl the opposite direction from what we expected, she told us that the sink needs to be a perfect circle. Otherwise the sides will cause interference. How convenient.

I'm the new Physics To Go intern, and I'm obviously a giant nerd if the first thing I did when I got to Australia was attempt a doomed physics experiment. As you might gather from the first half of my screen name, astropixie, I'm obsessed with astronomy, so I'm majoring in physics in college. The second half of my screen name comes from an obsession with fairies, which comes from an obsession with Shakespeare. Yes. That's right. I'm also an English major. Stop giving your screen that weird look—it's actually a useful skill set for my new position. Physics To Go is a collection of physics resources as well as a biweekly magazine—every two weeks the homepage features new outstanding webpages from the collection, grouped around a certain topic in physics. I help maintain Physics To Go by looking for and cataloging informative sites to post on the homepage. My internship is awesome. And I realized my internship was awesome after looking into the Coriolis force for a new homepage.

One upcoming homepage will be on the Intertropical Convergence Zone, or ITCZ (pronounced "itch"), an interesting weather region near the equator which is caused largely by the Coriolis force. While the turn of the Earth won't prod sink water one way or the other, it does affect the direction of trade winds in the northern and southern hemispheres. When these different patterns meet in the middle, it creates a belt of turbulent weather.

Anyway, looking at all these websites about "fictitious" forces made me relive my folly. I had many concepts in my head exactly backward or at least seriously confused for far too long. I finally feel like those mysterious terms at the end of equations from dynamics class have been resolved in my head thanks to these sites on the Coriolis force and the centrifugal force, which I would never have found if I weren't putting together a page on the Intertropical Convergence Zone. (Be sure to see how you can pretend to demonstrate the Coriolis effect with the sink "experiment" from Bad Coriolis if you’re sinister like that.)

Now you know why my internship is awesome: I'm learning new things while helping others learn, too. Right now I’m working on multiple homepages at once: the ITCZ page, a page on quasicrystalline patterns found in Islamic mosque art, a page on atmospheric scattering, and I just finished a homepage about the Crab Nebula, which is on the site now. It doesn't get any better than that.

(By the way, my results in Australia were inconclusive. The gum wrapper kind of spun sadly in place before coming to a soggy rest by the drain. I couldn’t tell which direction the water was going without something floating on it. I didn't have any more gum to run more trials. Soap bubbles went everywhere with no trend. And don't ask why I never tried to do the "experiment" on my own in the northern hemisphere. It only occurred to me to try it in Australia.)

By astropixie


  1. The ITCZ is formed as a result of convection, not the coriolis force.

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  3. Let me explain what I meant. (I'm backing up a bit here for the benefit of others.)

    Warm, moist air from the equator rises and creates a low pressure region. The air flows toward the north and south poles. As the air rises, it cools and sinks back down, filling the low pressure region from both directions. This page has a pretty good explanation: http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/hadley_cell.html

    If you look at the picture on this page, you'll see that the trade winds are all pushed westward. This is thanks to the Coriolis force; large wind patterns in the northern hemisphere curve right, and they curve left in the southern hemisphere. So the winds are meeting in the middle because of convection, but they are also moving in the same direction because of the Coriolis force.

    Thanks for bringing this up. The July 16 issue of Physics to Go will have more information.

  4. Awesome on the dual-non-related majors. I'm Aerospace and Fine Arts (specifically drawing and print-making). I wield amazing powers of visual explanation of complex designs. Plus I can paint a mean butterfly.