There is a video out (can't link) of a dust devil cyclone at a music festival in Australia, a low pressure atmospheric event rotating counterclockwise as they do in the Northern Hemisphere. Am I missing something?
Apparently so. There is no reason to suppose that small vortices of either air or water (e.g. a whirlpool or the vortex of an emptying bath) rotate in a direction determined by which hemisphere they are in. That's just a popular myth. It is however the case that the direction of rotation of large air systems, such as cyclones, is determined by the Coriolis effect and therefore goes in opposite directions in different hemispheres. It is all to do with whether the Coriolis effect is the dominant influence or not. If not, then any chance eddy, for example caused by the edge of a building, or a water current, can set the rotation going, and this can thus be in either direction.
thank you! it was reported that near the equator, probably Nigeria, people con tourist by stirring water in basins, pails to have them rotating according to hemispheric preference. so: size matters?
What matters is whether the motion is on such a scale that the Coriolis effect becomes significant. When you have masses or air in motion over distances of 50-200km or so, then yes the Coriolis effect is quite important. But if the motion occurs over a range that involves a negligible change in the tangential speed of rotation of the Earth beneath, such as the 10cm-10m scale involved in an emptying bath or a small whirlwind, then, no it isn't. The Coriolis effect is important in naval gunnery, in which shells are sent distances of 20km or so, but for an archer shooting an arrow 50m, it's negligible.
Right you are. Even super cell thunderstorms and tornadoes will rotate against the coriolis effect (clockwise in the northern hemisphere) about 5% of the time.
This is a scam. As the con-man walks among the tourists, he makes sure that he has made a complete circle. This is all it takes to make the water rotate. This trick is usually performed right at the equator, with the con-man demonstrating the water rotating in one direction on the south side, and in the opposite direction on the north side. So close to the equator, the force is so small that even an extremely sensitive instrument would not be able to measure it. And by the way, we now call it the Coriolis force, not the Coriolis effect. It is, indeed, a force. North-south running railroad tracks wear out faster on one side than the other because the Coriolis force pushes the cars very slightly in one direction. The observation that water in toilets spins the opposite way in the two hemispheres may or may not be true, but it has nothing to do with the Coriolis force. It's a matter of how the receptacle is designed. The water is forced out of the tubes in the ceramic, and this force is many orders of magnitude greater than the Coriolis. Perhaps Australian toilet manufactures just happened to design their appliance with the tubes pointing in the opposite direction from their American counterparts. Or what the heck, maybe they did it on purpose just to amuse Bart Simpson. Please Register or Log in to view the hidden image!
I actually calculated the lateral force from a 100tonne loco heading due South at 100kph - it was about 140N, i.e. ~14kgf. So I have to say I am sceptical of this story about railway tracks. Do you have any reputable reference validating this? I could not find one when I tried.
Sorry, that's from several decades ago, and I do recall that the writer didn't give a source. You're probably right then.
If you Google Railroad Track Coriolis there lots of sites agreeing that the tracks wear unevenly and the sites seem legitament.
Yes I know, I did this too, but was surprised that I could not find among them anything from a railway engineering or maintenance organisation, just a load of physics forums all reciting this fact - or factoid. Which is why I made the calculation. I suppose it is possible that a lateral force of 5-15 kgf over a long period may cause differential wear, but I'd be a bit surprised, as it does not seem much.
I don't know the service life of steel rails, but I'm sure some of those tracks were laid 100 years ago. That might be long enough.
would not a north going train put strain on the east rail, and a south going return trip on the west rail? in the northern hemisphere?on a single track line?
Yes, but most railways are double track - at least in countries where rail travel is taken seriously and the trains go fast enough for a Coriolis effect to be worth considering. 20mph freight trains in the rural USA or somewhere are not really relevant examples. The TGV from Paris to Marseille is the sort of scenario where it might be significant: http://forums.futura-sciences.com/s...-samusant/490765-tgv-lyon-paris-coriolis.html These guys work out 50kg force per wheel, assuming a 450t train at 320kph (200mph). That's a serious train.
