Cable Forum - Down the Plughole

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Re: Down the Plughole

Condensing what I found in passing... coriolis effect applies under laboratory controlled conditions, but in real life other perturbations are likely to start the rotation in one direction or the other.

Re: Down the Plughole

Quote:

Originally Posted by Matth (Post 35766416)

In a sink, bath or anything with a plug, the removal of the plug will most certainly start a vortex disturbance, by simple volume displacement and if the plug tilts, which it always does, you get a paddle effect created by the upward pull and hence a rotating vortex.

Bang goes the rather likeable myth.

Re: Down the Plughole

Seems like there's plenty online to suggest it is a myth, for example from Wiki (which although I'm sure you'll point out can be edited by anyone)..

Quote:

Contrary to popular misconception, water rotation in home bathrooms under normal circumstances is not related to the Coriolis effect or to the rotation of the earth, and no consistent difference in rotation direction between toilet drainage in the Northern and Southern Hemispheres can be observed.

Re: Down the Plughole

And funnily enough, UCL, one of the world's leading Universities, think it's a myth as well....

http://www.ucl.ac.uk/maths/research/fluids-gateway/faq

Quote:

Is it true that water goes down the plughole with the opposite spin in the Southern Hemisphere?

No, well maybe, but it has nothing to do with which hemisphere you are in.

It is true that because the Earth is rotating, the Coriolis force has an effect on the motion of water, and this effect is reversed between the northern and southern hemispheres. However, the importance of this effect is measured by a number known as the Rossby number, R, which is the ratio of the average speed of the fluid and the product of the rate of rotation of the Earth (at a particular latitude) and the length scale of the motion. Flows with small Rossby numbers are strongly affected by the rotation of the Earth, while those with large Rossby numbers are not. If we consider a sink that is 30cm wide in London and assume that the water flows at approximately 10cm/s, then the Rossby number of the flow would be close to 10000. Basically, this has no bearing on the direction of the flow. The biggest effect you’ll see comes from the initial direction of the flow and the symmetry of the basin, which could very well be different depending where you are in the world.

Re: Down the Plughole

That episode of the Simpsons has a LOT to answer for it seems.

Re: Down the Plughole

Seems like the consensus of opinion is that it is a myth.

We need a few Aussies on the Forum.

Re: Down the Plughole

Well I suggest most people don't care either way..There are much more wondrous things to observe in the world and the universe. ;)

Re: Down the Plughole

Quote:

Originally Posted by Maggy J (Post 35766510)

Well I suggest most people don't care either way..There are much more wondrous things to observe in the world and the universe. ;)

Yup - like ME!!!!!! ;) :)

Re: Down the Plughole

Quote:

Originally Posted by Wittmann (Post 35766509)

Seems like the consensus of opinion is that it is a myth.

We need a few Aussies on the Forum.

I worked in Auckland 12 months in two years, and there was no discernible different pattern - sometimes one way, sometimes the other.

Re: Down the Plughole

I'm guessing it depended on what you ate...? :disturbd: