One interesting Physics related observation that Physics Wong did not teach
us but Simpson's, PBS/BBC TV special, Michael Palin's "From Pole to Pole",
NPR (National Public Radio), and sports Illustrated brought up is the fact
that water in a sink (or toilet) rotates CCW (counter-clockwise) and CW
(clockwise) in northern hemisphere and southern hemisphere respectively. All
the above cited sources claimed the observation is due to Coriolis
Force/Effect. I checked the rotations in the toilet many times while down
under. It does work; however, when I consulted "Google", the cat came out of
the bag. The observation of the direction of the rotations is correct, but
the reason is not. Using Coriolis Force to explain the rotation directions
of hurricanes, typhoons, is correct because the word "cyclonic" means that:
1) the fluid (air/water) rotates in the same direction of the underlying
Earth (i.e., CCW in northern hemisphere, CW in southern hemisphere).
2)
The rotation of the air/water is due to the rotation of the Earth. It is not
correct to assign the same Coriolis Force/Effect for the toilet-flushing
rotations if one recognizes the magnitudes of the vastly different angular
velocities of Earth (once per day, or slow), and the draining toilet (a few
seconds if not clogged, or fast). It should not be surprised that the
Coriolis Force is 8,640 times larger in a hurricane than a ten second flush.
The number 8,640 comes from one day's 24 hours, or 86,400 secs, and the 10
sec flush. To quantify the different force magnitudes, one needs to
introduce Rossby Number, a
dimensionless ratio of inertia force to Coriolis force. It suffices to say
that the Rossby Number is inversely proportional to angular velocities
(Earth's rotation has a large Rossby Number, and toilet flushing has a small
Rossby Number).
In passing, I like to bring up another Earth's angular velocity called
"Chandler's Wobble". It is 433 days per cycle, or 20% slower than the one
year we all know. It was discovered by Seth Carlo Chandler Jr. in 1891. He's
an astronomer turned businessman. When S.S. and I were picking pears in '60,
there was one NTU (National Taiwan University) graduate in geology (Cheh
Pan潘哲). He went on to Colorado School of Mines and MIT. In fall 2001, he
presented a poster "The Rotation of Nonrigid Earth". He described briefly
his 1963 thesis "A Preliminary Study on Relations between Polar Wandering
and Seismicity". He told me that the wobble stopped couple days in 2004, and
now he's writing a paper in his retirement on the subject he left off more
than 40 years ago. Old soldiers never die, they just fade away. Old
scientists never stop
writing, they just keep on grinding. Happy New Year and many returns! |
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