Which way does water flow on the equator?

September 4, 2004 1:43 PM

So, in the southern hemisphere water flows one way down the toilet and in the northern, the other. What happens on the equator?
posted by Mossy to science & nature (11 comments total)

Great question, except the premise is false. The Coriolis Effect only applies over very long distances, as in hundreds of miles. Over the distance of a (toilet) bowl, it has no effect.

Apparently, the guys who "demonstrate" the Coriolis Effect at tourist spots near the equator are good at tipping the bowl ever so slightly to start the water flowing in one direction or another.
posted by argybarg at 1:47 PM on September 4, 2004

It's a myth that water drains one way in the northern hemisphere and the other way in the southern. Try running several tests where you fill up your bathroom sink and then drain it. You'll find it's random which way the water goes.
posted by cardboard at 1:48 PM on September 4, 2004

The Coriolis force has no significant effect on small fluid volumes. But if it did, I imagine the toilet would simply drain without any twisting effect.
posted by Galvatron at 1:51 PM on September 4, 2004

Even though the Coriolis thing is bogus, there is a cool hemispheric phenomenon you can evaluate right now, assuming you don't have a flat panel display: turn your color CRT monitor upside down
posted by tss at 2:15 PM on September 4, 2004

Check out this for a good explanation and a sweet movie demo.
posted by sciurus at 3:12 PM on September 4, 2004

I don't understand the monitor issue. I've used the same monitor in the US and Australia, with no noticable difference.
posted by croutonsupafreak at 4:46 PM on September 4, 2004

Not just CRT monitors, but I believe TVs are available in northern and southern hemisphere versions (or come with the switch that slightly turns the image). The difference is tiny, however, and you'd generally be pushed to notice it.
posted by wackybrit at 5:14 PM on September 4, 2004

we use monitors shipped from the north here in chile. as far as i know there's no adjustment made.

unless you're near the poles, the magnetic field is largely parallel to the surface of the earth and running n/s (or s/n - no idea which). changing hemispheres would only alter the vertical component of that (small effect), while rotating your tv through 90 degrees (w to n, say) changes the whole shebang (large effect). so, unless i'm confused (possible), swiveling your monitor round on its base is a much larger effect than sending it south.

when you physically turn it upside down you're probably seeing the results of flexure from gravity.
posted by andrew cooke at 6:27 PM on September 4, 2004

hmmm. not sure about the part of my argument that says the vertical component is small. but as long as the horizintal component is at least similar in size (which is must be, away from the poles) the rest holds true - rotation is at least as strong an effect.

although, thinking more, there's something about the direction tat may be relevant. the horizontal component of the field, whose influence varies as you swivel, will shift the beam vertically. the vertical component. whose influence varies as you travel n/s, will shift the beam horizontally. and i could imagine that trinitron tubes are much less sensitive to vertical errors than horizontal errors.
posted by andrew cooke at 6:31 PM on September 4, 2004

bleagh. i do know the difference between affect and effect, and between commas and full stops. but my brain developed in the northern hemisphere, down here the synapses are confused by the changed magnetic fields...
posted by andrew cooke at 6:34 PM on September 4, 2004

My college physics is a bit fuzzy, but I seem to recall that the electric potential imparted by a magnetic field is perpendicular to the magnetic field. So if the earth's magnetc field flows approximately along its surface, then the electron deflection would be either up or down. But the force wouldn't switch direction when you cross the equator.

when you physically turn it upside down you're probably seeing the results of flexure from gravity.

With sony monitors in particular, rougly tapping on the side of your monitor will significantly distub the colors. This is because the "screen" is made of thousands of tiny wires, all running in parallel (and one or two perpendicular wires to keep them together and spaced properly). Inverting a monitor may offset the shadow mask by just enough to change the picture. Sony trinitrons would need to go on their side, to offset the aperture grille.
posted by b1tr0t at 6:46 PM on September 4, 2004