Wednesday, May 03, 2006

The direction water goes down the drain.

So, here's the proof that I'm a giant geek. I'm traveling right now, so I'm writing this from a room in The Hotel Monaco in Seattle. This room is pretty nice and it actually has a giant whirlpool tub. When I say giant, I mean it. This thing is deep. I was able to fill it reasonably full and be nearly ass deep in water. If you are staying in a place like this it is silly not to take advantage of the amenities. I decided that I should grab a soak in the tub.

When I was young, rather than an actual pool, many of my friend's parents bought cattle tanks to use as pools. I know this sounds pretty low rent, but it is pretty common where I grew up. The tanks are usually about twenty feet in diameter and about 3 foot deep. One of the fondest memories of these tanks is when a group of kids would take up spots along the rim of the tank and we'd all walk in circles until we'd got the water moving in a giant whirlpool. After we got the water going at a good clip, we'd plop down into the water and let it carry us around in circles. This is one of the simple pleasures that I remember from being a kid. In an attempt to recreate this experience I directed all ten of the whirlpool jets in the same direction while I was in the tub. The results were less than spectacular. I got out and dried off. After I was half dressed, I noticed that I'd left the tub running. I went into the bathroom and found that the whirlpool tub was living up to it's name. The water had formed a wonderfull little whirlpool. There was a nice three to four inch deep indentation in the center of the water. I then drained the tub and that's when the magic started. OK, not really magic, but it was cool anyway. A column of air formed from the surface of the water all the way down to the drain. The colum was at least four inches at the top and narrowed to about two inches at the drain. What was even cooler was that the funnel was completely stable with almost no ripples.

This put an idea in my head. What if the jets are pointing the other direction. Fifteen minutes later I had the jets reconfigured and the tub refilled. I wanted to see if the same results happened if the water was spinning the opposite direction. It took another ten minutes to get the water spun up with the same four inch dimple as before. Now, here's the interesting part, when I opened the drain, I didn't get the same beautifuly symetrical whirl pool as I'd gotten earlier. The whirlpool with the opposite rotation whipped around wildly and wasn't nearly as wide as the one earlier.

I did some poking around and didn't find anything conclusive to explain this. From what I've read, the corriolis effect is quite negligible. This is obvious since the tubs maintained the draining direction established by the orientation of the spin of the water. I guess the small differece made by the corriolis forces could have a destabilizing effect on the whirlpool.

So the fact that I spent almost 45 minutes filling and draining a tub to do an experiment that was nearly meaningless is probably proof that I'm just about the biggest nerd you've ever seen.

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