Eddys In My Bathwater

We are fortunate in many ways to have a rich and diverse set of opinions and knowledge among the regulars at the Kings Arms…

This means that even the most trivial of topics often become the subject of close scrutiny analysis and (often) heated debate, with the miracle of 3G Internet browsing on our mobiles often, but not always, providing a definitive solution to the issue at hand when the shouting is over.

Yesterdays topic was the oft debated urban myth that water flows down a plughole in different directions depending on what hemisphere of the earth you are on.  The vast majority of the lunchtime crowd, including Spike, Captain Kidd and Teaching Assistant Tom agreed with the hypothesis, leaving poor barman Dom a lone voice in the wilderness crying for the truth to be heard – at least until I arrived.

The internet was consulted, and apocryphal tales from various merchant seamen appeared to back up the theory, as well as that fount of all knowledge – an episode of the Simpsons ‘Bart vs Australia’, Episode 119 first aired on 19/2/1995.

The process that would seem to be the likely candidate for causing this phenomenon appears to be the Coriolis Effect, which in a nutshell is a consequence of the earth spinning on its axis and dragging everything else around with it, with inertia coming into play – it’s complicated.  The Coriolis effect is what causes hurricanes to rotate, and has to be taken into consideration when firing artillery shells, for instance, but it’s effect in small closed systems (like a bathtub emptying when you pull the plug) is negligible at best, and can only really be measured under very strict, controlled circumstances.  Indeed, this Wikipedia articledescribes an experiment where the consequences of the Coriolis effect was actually seen to affect the direction of the vortex formed when the water drains from a container.

However, in that case the fluid had been left to settle for 24 hours, and the temperature was kept constant so that no other forces could be influencing the results – the article begins ‘It is a commonly held myth that the every-day rotation of a bathtub or toilet vortex is due to whether one is in the northern or southern hemisphere.’

I think in terms of water pouring out of the bath or sink, there are far too many factors (for example, the shape of the container, the wildly fluctuating temperature gradients throughout the fluid causing spontaneous convection currents, general movement of the fluid) affecting the flow of water toward the plughole for the Coriolis effect to be a factor in what direction the water will spin round the hole.  Fluid dynamics is perhaps one of the most complex physical processes to model and measure – the fact that the Meteorological Office has access to some of the most powerful supercomputing facilities in the country and still can’t predict the weather accurately over a period of more than a couple of days is testament to that.

So, in a way, everybody is right, as long as they state that when they have personally witnessed the effect, they mention the fact that it was under strict laboratory conditions, with a decent sample rate and on both sides of the equator.

Otherwise, I fear they may be talking bollocks.

End Note

In the course of writing this, I researched the subject quite thoroughly, reviewing both anecdotal data and scientific observation.  I settled on the conclusions of the Wikipedia article as Wikipedia, while some naysayers might doubt the accuracy of some of it’s articles, it is subject to quite meticulous peer review, so I would trust it’s fairly unbiased conclusions as much as anyone elses. 

Anyway, Stephen Fry said it’s bollocks as well, so there!

2 Comments

• By Miss matchmaker, March 9, 2010 @ 7:25 pm

  NEVER MIND ALL THIS BATHWATER BOLLOCKS I JUST FOUND OUT WHO HATTY IS AND NOW IM 100% CONFIDENT I CAN TAKE HER LETS ORGANISE THE JELLY FIGHT – !
• By Fanackapan, March 17, 2010 @ 1:46 pm

  Ooh… time for action!

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