Sunday, 6 February 2011

Water - clockwise or anticlockwise?

As everybody knows, the Coriolis effect is the reason that water spirals in a particular direction when it flows out of a sink. Anticlockwise in the northern hemisphere, clockwise in the southern hemisphere.

However - it seems that the reality is actually very different. Apparently, the Coriolis force is orders of magnitude too small to have a significant effect on water exiting a sink and the direction of the vortex is largely determined by the shape of the sink, location of the plughole, any movement in the water etc. (This is in contrast to the case of large scale weather systems (hurricanes etc) where the Coriolis effect IS significant).

I’ve checked what happens in our kitchen sink (“north facing” plughole) and found that the water seems to exit in a clockwise direction - and that I can provoke it into going clockwise or anti-clockwise by giving the water an appropriate gentle stir prior to removing the plug.

Interestingly, a 1960’s paper in the journal Nature described how the Coriolis effect could be detected when a 600 gallon tank of water was repeatedly filled and allowed to settle for 24hrs. In this case, no rotation was seen for the first 12-15mins but after this an anticlockwise vortex did form and was found to rotate at approximately 30,000 times faster that the rotation of the earth, suggesting that the small Coriolis-induced effect was accelerated by gravitational acceleration and conservation of angular momentum effects (“conservation of angular momentum” is the way in which, for example, a spinning ice-skater will spin faster if they bring their arms close in to their bodies).

Just goes to show how “common knowledge” can be anything but!

You can find out more about this at the following :

This topic is also covered in a book titled “The Book of General Ignorance”, based on the “QI” BBC TV series and written by John Lloyd and John Mitcheson.

One other item in the book that caught my attention related to Radiation Tolerance, Apparently, tests in 1959 discovered that whilst a radiation exposure of 100rads will kill a human, cockroaches can survive up to 20,000rads, and some wasps don’t kick the bucket until they have been hit with 180,000rads. However, these are all far outclassed by a simple single celled organism (Deinococcus radiodurans) that can survive some 1.5million rads. Winningly, it is known by those studying it as “Conan the Bacterium”.

Scientists - who says they don’t have a sense of humour?

1 comment:

  1. very nice to see that you want to make sure that what you know is true