Mythconceptions: Hemispheres and Toilet Drains

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Welcome back to The Bent Spoon’s look at “mythconceptions;” that is, commonly held beliefs that are actually false.  While I thoroughly enjoy reading new pieces of information that fit into this category, I get an even greater joy out of discovering something that I myself have long believed that is actually not true. Today’s topic covers one such instance.

How many of you reading this have heard of the Coriolis force, or Coriolis effect?  It’s okay if you haven’t.  Up until a relatively short time ago I hadn’t either.  Though you may not recognize the scientific sounding names, you’ll probably be familiar with the effect they are said to create.

First, a definition. The Coriolis force, according to the Oxford American Dictionary, is “an effect whereby a mass moving in a rotating system experiences a force (the Coriolis force) acting perpendicular to the direction of motion and to the axis of rotation.”  It continues, “On the earth, the effect tends to deflect moving objects to the right in the northern hemisphere and to the left in the southern…”

While this force is important in the formation of cyclonic weather systems, it is also pointed to as the cause for toilet and sink drains in the Southern Hemisphere draining clockwise, while drains in the Northern Hemisphere spiral counter-clockwise.

The problem?  That is simply not true!  It’s a classic case of mythinformation.  The truth is the Coriolis effect has nothing to do with how sinks and toilets drain because the direction water spirals down in sinks and toilets is determined not by gravitational pulls, what Hemisphere you happen to live on, or anything of the sort.  Instead, it is determined by plain old ordinary structural conditions.

In their textbook, “The Atmosphere: An Introduction to Meteorology,” authors Lutgens, Tarbuck, and Tasa (2006) write, “…a cyclone is more than 1000 kilometers in diameter and may exist for several days.  By contrast, a typical sink is less than a meter in diameter and drains in a matter of seconds. On this scale, the Coriolis effect is miniscule.”  It’s the shape and how level your sink, toilet, etc. is that causes the direction of the water drainage, not your position on the globe!

I thought about this myself and concluded that, if this is true, the sinks and toilets in my house might just drain differently from one another.  If they did, the idea of water drainage being affected by the Coriolis force would be, well, flushed right down the drain.

So, that’s exactly what I did and, wouldn’t you know it, that is precisely what happened.  I filled two sinks and flushed two toilets.  While the toilets each flushed in a counter-clockwise spiral, the sinks did the exact opposite; draining in a clockwise manner.  How foolish of me that, for years, I believed in the effect of the Hemispheres on our drains while concrete evidence to the contrary was there in front of me all along.  I just never paid attention.  But, at the same time, it was very satisfying to know the truth.

It is the moment of enlightenment that I had myself regarding this issue that I hope to bring to you with some of the “mythconceptions” I write about here from time to time.  Maybe you’ll even be inspired to fill a couple drains and flush a few toilets to check it out for yourself.  We’re all wrong about stuff here and there.  We’re human.  But knowing the truth is great.  One of my favorite things in life are those simple moments of time where I stop and realize, “Everything I thought I knew was wrong…and it’s awesome!”  

If you’re anything like me you’ll agree.