Drain vortices and religion

[CORed]

The vortex above a sink or bathtub drain rotates counter-clockwise in the northern hemisphere, and clockwise in the southern hemisphere, due to the Coriolis effect. This "scientific fact" is something that most of us were told at some time during our education. On the surface, it seems to make sense. A drain is, after all an area of low pressure, and it is well known that atmospheric low pressure systems rotate in the manner described.

There's just one problem. It isn't true. The next time you finish a tub bath, or finish doing the dishes, watch the vortex that forms while you are draining the sink or the tub. If you do this several times, you will observe that the vortex sometimes rotates counter-clockwise, sometimes clockwise. If you keep records and gather a big enough sample, you will probably find the ratio of clockwise to counter-clockwise vortices is pretty close to one.

How can this be? Well, the Coriolis effect is quite significant in an air mass that is moving several hundred miles, but, for a bit of water that moves only a foot or two, it is negligible. The drain vortex is generated by conservation of angular momentum. In the course of filling the tub or sink, doing the dishes or taking your bath , and even of pulling the plug out to drain it, you will induce some motion in the water. Since it's in a confined space, and will be turned by the wall of the tub or sink into a rotating motion. You may have more or less the whole sink rotating in one direction, or you may have several swirls in different directions, but the water is never going to be completely motionless. When one of these swirls gets pulled into the drain, the rotation will speed up, much like a spinning figure skater when she pulls her arms in, and pretty soon, you have a nice little vortex, a miniature tornado, spinning in your sink or tub. The direction of rotation is pretty much random. In fact, if you generate a vortex by moving your had through the water, and send it over the drain, you can reverse the rotation of the drain vortex. Try it. It's kind of fun.

What, you may ask does this inconsequential bit of trivia have to do with religion? Well, something I find fascinating is that a pretty high percentage of the population believes that drain vortices always rotate in a particular hemisphere-depenant direction, in spite of the fact that simple observation of an everyday event would demonstrate that it's false. It seems that a lot of people are more willing to believe something because a parent, teacher, or other authority figure told them it's true, than believe the evidence of their own senses. This silly little "scientific" myth gets passed down from generation to generation, and most people never notice that it ain't so.

[Ben K]

Didn't know that the coriolis effect was too small. Took it on faith that my science teachers knew what they were talking about.

Thankfully, thousands of people are not killing each other over their beliefs on vortex directions so it's not so much of a worry.

You are right on religous types mostly depending on what they're told. Even those who've researched more deeply still create their 'unique' viewpoint based on that prior invented rubbish. It's not like they have any facts after all...