Spin-Drift

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It just happens that it is possible to convince ourselves that our Earth is spinning on its axis (don't ask with respect to what?) without looking out Heavenwards.

1. Let us take that man-eating shark that launched Cecil Rhodes on his Empire.

Let us say that she sets herself on her swimming spree at the Equator in shallow waters. Let us forget the ocean curents for the moment. Let us suppose she starts due North and plans to reach the shores of England to eat up that poor patriotic German. Since the Earth spins from West to East, she has an Eastward speed at the start of her mission at the Equator. By the time she reaches the English latitudes, the Eastward speed of the English shores due to the spin of the earth is almost reduced by half because the circle of spin at these latitudes is that much smaller. So, she is carried away by her initial Eastward speed more than the English shores. If she forgets to correct for this difference in speeds due to the spin of the Earth, she would land up squarely on the English beaches, get killed, cut up and robbed by the fishermen on the beaches...poor fish!

This spin-drift depends on how long she takes to reach her destination. At worst it could be about 5 KM and much more if she lingers.

Had she changed her mind at the outset and sets due South to land up in Australia for her man-meal, the same thing happens and she would lead the Earth at Australia and would land up on their beaches.

This is direct evidence of the spin of the Earth that could be felt by not only sharks but sailors as well. Both have to make corrections if they don't want to drift away at sea and mess up their landings.

2. From the shark's point of view, the drift she feels in her Northern hemisphere would be towards her right, both onwards to England and return back to the Equator .

On the other hand on her Southern journey the spin-drift would be continually left-wards.

What is true for the shark is also true for the winds from the Equator to the tropics and away.

That is why we have the wonderful fact that cyclonic circulations are always clockwise in one hemisphere and anticlockwise in the other!

Here is more proof:

3. Let us take a naval long-distance artillery gun. What is true for the winds and sharks is also true to the shells. If the gunner fails to take into account the spin-drift, the shells would go astray and blow up maybe on friendly ships.

Oh, no!

4.. Let us take a pendulum suspended on the North Pole and set it into its oscillations. It would go on in the same plane as seen from space. But a girl on the ground near the North Pole would be going round in a tiny circle once in 24 hours if the earth really spins. So, for her the pendulum would be turning the other way in its plane once in 24 hours.

But if she does the same experiment on the Equator, the turn would be clearly nil.

In between, at Paris the continual shift in the plane of oscillations of the pendulum would be about once in 43 hours.

This was demonstrated by Foucault by his celebrated pendulum at Paris, a great draw for the crowd (I read that recently Foucault's original pendulum fell down and is yet to be reinstalled).

5. Let us go to Singapore which is right on the Equator. Let us get on to a skyscraper and mount on its top. And drop a stone vertically down. We would expect it to land plumb at the skyscraper's foot.

But consider: the roof is a wee bit at a greater distance from the center of the Earth than the ground. And so the top whirls a little faster than the ground. So, the stone has a bit more Eastward speed than the ground. So, it would land a bit more eastward than expected.

I guess the difference is too small to be directly measured, but the principle is ok.

Samuel Johnson wrote an essay: 'The advantages of living in a garret'. Garret is the very top floor of a multistory building. Somewhat like a cramped attic. So, garrets were rented much cheaper than the lower posh floors of London. And these were all the poor prospective writers and poets could afford.

Johnson makes a virtue of this necessity by saying that the budding writers prefer to live there because the spin of the Earth makes their brains whirl a little faster and they get exhilarated by the speed of the garret and it goes to their brains and gives them the kick needed for their inspired blogs.

Oh, well, you know why my blogs are so insipid: we live on the ground floor; IIT KGP gives us just enough pension.

But of course, Hyderabad is at a height, and that more than makes up for the advantage got by the poor bloggers who can only afford the pent-houses of Chennai!

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