Saturday, October 31, 2009

coriolis effect - water spins n vs s of equator ??

as we already saw, the Coriolis effect
only produces a measurable effect over huge distances and long
periods of time. Even the most decadent of bathtubs is thousands
of times too small and drains way too quickly to ever be affected
by it. It can be shown mathematically that random motions in
your water are thousands of times stronger than the Coriolis effect,
which means that any random eddy or swirl in the water will completely
swamp it. If the water always drains one way from your
bathtub, then it has far more to do with the detailed shape of your
drain than from the rotating Earth.
Obsessive would-be physicists have actually performed experiments
using household sinks. They have found that the sink needs
to sit still for over three weeks so that random currents die off
enough to see an appreciable Coriolis effect. Not only that, they
have to let the sink drain one drip at a time to give the effect time
to take hold. You’re not likely to see this after hand-washing your
delicates in the sink.
The same is true for your toilet. This one always makes me
laugh: toilets are designed to spin the water. It helps remove, well,
stubborn things that don’t want to be removed so easily. The water
is injected into the bowl through tubes that are angled, so it always
flushes the same way! If I were to rip my toilet out of the wall and
The Coriolis effect is only significant over large
distances. A hurricane is born when a low-pressure
patch of air draws air in from higher and lower
latitudes. Because of the Coriolis effect, in the
northern hemisphere the air from the south moves
east, and the air from the north moves west,
causing a clockwise rotation.
fly it down to Australia, it would flush in the same direction it
does now.
The idea that the Coriolis effect works on such small scales is
a pernicious myth. I have seen it in countless television shows and
magazine articles; it was once even reported in the Sports Illustrated
swimsuit issue. Oddly, they describe walking across the
equator from the Central American country of Costa Rica, which
is hundreds of kilometers from the equator. Some writer on staff
did the figures incorrectly, but then, those aren’t the kind of figures
the magazine is usually trying to sell. On the other hand, maybe all
that walking is how the models stay so slim.
So, if the Coriolis effect doesn’t work on something as small as
a sink or a pan, how did Peter McLeary pull it off? After all, as
Michael Palin commented, it worked for him.
Actually, McLeary cheated. If you watch him do it on Pole to
Pole, you can catch the swindle. He stands on his equator line and
fills the basin. Then he walks a few meters or so north, and rapidly
turns to his right to face his audience. He opens a hole in the
bottom of the pan and the water obligingly rotates clockwise as it
drains out. Next, he refills it, walks a few meters south of the
equator, then rapidly turns to his left to face the audience. Draining,
the water spins counterclockwise.
Do you see how this works? By spinning rapidly in opposite
directions, he can make the water rotate any way he wants! The
squarish shape of the pan helps, too; the corners help push on the
water as the pan rotates, making it flow better.
Meteorology professor Alistair Fraser has used this demonstration
in his own class. He draws a line down the middle of the
classroom and declares it to be the equator (he teaches in Pennsylvania).
He then does just what McLeary does and gets the same
Still don’t believe me? Then think about it: the Coriolis effect
should make draining water spin counterclockwise in the northern
hemisphere and clockwise in the southern. In the northern hemisphere,
water moving north deflects east, moving it counterclockwise.
Water coming south from the north deflects west, but that’s
still counterclockwise. The opposite is true again for the southern
hemisphere; the water will spin clockwise.
But this is precisely the opposite of what McLeary demonstrates.
He’s a fraud!
Your honor, I rest my case.
Well, not really. I have one more tale to tell. While searching
for information about Nanyuki, I found one tourist’s travelogue
that describes three sinks sitting roughly ten meters apart, just outside
of town. One is south of the equator, the second is directly on
it, and the third is north of it. Perhaps someone else is horning in
on McLeary’s act. Anyway, the tourist who wrote the travelogue
claimed that the northern sink drained clockwise, the southern
sink drained counterclockwise, and the one in the middle drained
straight down. Evidently the drain holes have been cut in such a
way as to force the water to drain the way the designer wanted.
Note once again that they drain the wrong way!
It’s pretty funny, actually. They go through all that trouble to
make a few bucks, and they don’t even get the scam right. Somehow,
though, I don’t think those con artists are starving. Con artists
rarely do. They can always put the right spin on their subjects