The Missing Coriolis Effect

Uncle Thanky

New Member
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Senior Member.
The scale is too small in all 3 cases.
estimating the Rossby numbers here with orders of magnitude U ~ 1 m/s and L ~10 m resp. 1 m
the Rossby numbers here are about 1000 to 10000. Which means that the coriolis force has a small to negligible effect here
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Senior Member.
can you explain that to me in non-nerd speak? how come we see a swirl in the kitchen sink at times? vs. his experiments.

In basic terms, it means that the forces that control the vortex (swirl) in a drain are somewhat random, and because the drains are so small when compared to a storm system (Hurricanes) there's not enough size to always cause a vortex. Most vortexes seen in water are the result of water swirling around submerged rocks or where currents moving in different directions merge.

In Math terms:
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Senior Member.
It is a bit like the effect a frictional force will have on an object. For instance when you pull a table cloth from under a fully covered table rather slowly you will end up with a great mess. But if you do it very quickly everything will stay more or less in its place and you will get applause. Another factor is whether the tablecloth is rough or smooth. So the frictional force between the plates etc and the cloth won't be able to accelarate the plates depending on "cloth speed" and "smoothness". You might call the combination of the two the ratio of inertia to the friction force.
Likewise because the angular velocity of the Earth is comparatively small (once about every 24 hours) the question whether the coriolis force is able to "drag" things around depends more or less on the time it takes to cross the sink or the lake, which in turn is determined by the typical speed (say 1 m/s) and the length scale (say 1 m). The coriolis parameter f is 2(2pi/86164 seconds) x sin (latitude) and has on mid latitudes the order of magnitude of 1/10000
So swirls in bathtubs etc originate from initial movements in the water etc. that are strenghtened by preservation of angular momentum when the water moves inward (like an art skater making a pirouette) independent from the coriolis force.
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Mick West

Staff member
So swirls in bathtubs etc originate from initial movements in the water etc. that are strenghtened by preservation of angular momentum when the water moves inward (like an art skater making a pirouette) independent from the coriolis force.

The misconception about the Coriolis effect is used at tourist traps on the the equator to "demonstrate" they are moving across the equator. The huckster has a basin of water that they drain, showing a clockwise spiral. They then walk "over the equator" (which is generally not the exact equator anyway) and show that the basin drains the other way. It's just a trick where they force the direction of the spiral either in the initial filling of the basin, or by giving it a bit of a wobble.


Senior Member.
Another example that bears out Mick's point:

From accessed 15.02/2015

Flat Earth supporters often cite the "missing" bathtub coriolis, while strangely remaining silent about the evidence of large scale effects seen in weather systems, storms and hurricanes, which do reliably rotate in opposite directions in the northern and southern hemispheres.

They also keep quiet about the manuals for artillery directors and snipers that describe the need to take coriolis into account:

I've removed one example because the post has now been made private.
cited at
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Active Member
The Exposing PseudoAstronomy Podcast covered this subject in their latest episode.
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