Professor STH Abidi - A flood of Pleasant Memories

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Professor Abidi was the first member of our Physics Faculty I met with, as soon as I joined IIT KGP on May 1st 1965 (May Day was not a holiday then).

After giving my Joining Report, I was in the Physics Office to get to know  my duties.

And a fair, thin, handsome, spectacled gent of medium height arrived there to check his mails. 

And our Office Secretary, Sri Dulal Ghoshal, introduced him to me as Professor Abidi from Lucknow.

After shaking hands, Professor Abidi led me to the Co-Operative Canteen (then housed under the Netaji Auditorium) for the customary celebratory cup of tea.

There I found half a dozen of my future colleagues under the mango tree outside the Canteen; some standing, some sitting...all immersed in a group discussion of a paradox relating to the Archimedes Principle. 

That was a strange sight to me. I never saw any such thing at my university.

Professor Abidi introduced me to the group; and I came to know that it is the 'Canteen Physics Society' chaired unofficially by Professor Mohinder Singh Sikand.

And for the next 30 years till Professor Sikand retired, Professor Abidi and I were fixtures there. Just listening in would teach me the physics that is not easily found in books.

Pretty soon, I found that Professor Abidi was blessed with a charming personality. I never saw a frown on his face.

His lectures were most popular. Whether the class had 12 students or 120, he held them all spellbound. He was a most willing teacher. I guess during his 40 years there he must have taught all physics courses at all levels, except perhaps Electronics.

Professor Abidi was a silver-tongued orator. In every Farewell Function of the Department, he would be the lead-speaker, starting his speech with an Urdu Couplet composed by himself.

He was a born leader of men. When, in 1990, six of us were assigned to teach an inaugural Quantum Mechanics Course for the six  B Tech Sections, we elected Professor Abidi unanimously as our Course Coordinator for the next 3 years.

When the Old Building was renovated and turned into the Nehru Museum of Science and Technology, Professor Abidi was picked up as its Chairman. With Professor Mandakini Majumdar as the Secretary, the Museum  sparkled within a year. Numerous Working Models got housed in each and every room of that building. And a Steam Loco was brought from SE Railways as a gift. Also a Hunter plane from the Air Force Station in Kalaikunda. I specially loved an outdoor exhibit of two swings acting as Coupled Pendulums.

Monthly Exhibitions and Contests were held in which the Campus Community delighted.

Professor Abidi and Professor Mandakini Majumdar did me the greatest honor by publishing a writeup I had made for Professor GS Sanyal as the first Publication of NMST.

Professor Abidi had laudable administrative skills. Together with the legendary Professor Bhola Avasthi, his neighbor, Professor Abidi acted as Warden of several Halls of Residence. He had a way with students.

At one time the Technology Students Gymkhana used to publish two prestigious periodicals, Alankar (English) and वातायन (Hindi). I found Professor Abidi's articles and poems there once in a while.

Professor Abidi had amazing social skills. On every Diwali he would visit his friends' homes along with his wife (herself a published Urdu poet). And their friends would reciprocate their visits on every Eid. Once, Professor RS Saraswat took me to Professor Abidi's Quarters where we were fed sumptuously.

Professor Abidi's sense of humor is memorable.

Once, he was returning from the Canteen while I was heading there. He stopped me and asked me this question:

"Professor Sastry! One who has read four Vedas is called 'Chaturvedi'. Three Vedas 'Trivedi'. Two Vedas 'Dwivedi'. What about one who read zero Vedas?"

I said I didn't know. And he revealed his answer:

"A-bedi (Abidi STH)"

And then I asked him:

"What about the one who read only one Veda?"

He said he couldn't guess.

And I gave my impromptu answer:

"Bedi (Bhishen Singh)"

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Tides - 8

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"Sitting on that blessed rock near the Scandal Point on the Vizagh beach, I would see 4 tides every lunar month (two spring tides and two neap tides) on Amaavaasya, Shukla Ashtami, Poornima, and Bahula Ashtami.

And since my Earth is spinning around itself in 24 hours, I would see these high and low tides repeating every 6 hours.

Phew!"

At last we have succeeded in understanding the origin of ocean tides on Earth, somewhat.

Actually, the details of tides are infinitely more complicated.

What we have done is more like the Eka Shloki Raamaayan:

आदौ रामतपोवनादिगमनं हत्वा मृगं काञ्चनं 

वैदेहीहरणं जटायुमरणं सुग्रीवसंभाषणम् |

वालीनिर्दलनं समुद्रतरणं लङ्कापुरीदाहनं 

पश्र्चाद्रावणकुम्भकर्णहननमेतद्धि रामायणम् ||

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All of us know that our Earth, seen form outer space, is spinning lie a top. And we are clinging to its surface somewhat precariously.

Because we should experience a centrifugal force tying to throw us out into space. But we rarely feel it, because Earth's gravity pulling us towards its center overwhelms the centrifugal force.

That is because the spin of the Earth is so very slow...once in 24 hours. That makes the ratio o the two forces about a few parts in a thousand. Still, it can be detected by the lessening of the 'acceleration due to gravity'  at the equator compared to the poles. 

The theory of spinning tops in classical mechanics is very very complicated. The Guru-Chela duo, Felix Klein and Arnold Sommerfeld, used to go to the sea beach and collect pebbles of various shapes, spin them in their lab; and they came up with a 4-volume definitive text: "Theory of the Spinning Tops"!

John Perry's Demonstrations at the Annual Royal Society Exhibition (meant for lay spectators) can be found compiled in the fascinating booklet: "Spinning Tops and Gyroscopes" (I had read it with great gusto in the Central Library of IIT KGP).

Every child riding a merry-go-round in the Kid's Play Area feels the hilarious centrifugal force as soon as it is revved up. That is because the merry-go-round goes round once every second maybe (instead of once in 24 hours).

And all molecules (like the Ammonia molecule) spin themselves once in about a microsecond. So the quantum theory of polyatomic molecules can't do without incorporating the centrifugal and other 'ghost' forces, making an already complicated subject infinitely more complicated.

I happened to chance on the celebrated tome of Townes and Schawlow:

'Microwave Spectroscopy".

That was full of symmetric tops and asymmetric tops and stuff like that. That work of Townes led to the first Maser (the Ammonia Maser) and won him the Nobel for it.

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All of us who played with tops know that when spun fast on the ground, the axis of the top remains vertical ('sleeping top').

But soon, due to friction with the ground and air, the top loses its kinetic energy and its axis starts tilting towards the ground and goes round in a cone. 

This is called 'precession' of the top axis.

The cone's semi-vertical angle increases gradually. This is the 'nutation'. 

And finally the top topples and falls on the ground.

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Something similar (but not as catastrophic) happens with the 'spin axis' of our Earth as seen from space.

The axis doesn't remain static but precesses in the celestial sphere, with about 25 deg as the semi-vertical angle of its cone.

And the time period of this 'precession of the equinoxes' is about 26,000 years (I can wait).

It means that the present 'pole star' (Polaris) will no longer remain a pole star in a few centuries. That position is taken over by some other star in the heavens.

Till, after 26,000 years Polaris once again becomes our pole star.

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The theory of this 'precession of the equinoxes' is as complicated as any theory of the spinning tops...more so because our Earth is not a perfect sphere...more like an oblate spheroid (pumpkin).

There are many cosmic reasons why our Earth-Top precesses.

One minor actor is our oceanic tides.

The continual ebb and flow of the seas on the land against the friction between the beaches and the seas generates heat.

And this heat energy is lost by the Earth into space by radiation.

Also, the solid Earth itself is not immune to tides. Although we treated Earth as a rigid body, we know that 'rigid body' is an idealization...all bodies are deformable to some extent or the other.

That much for tides (for now)...

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Tides - 7

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Let us do a simple "Thought Experiment"...

I take a big wooden sphere, dip it in oil, and take it out so that the wooden sphere is covered with a thin uniform film of oil.

And I place this sphere at the center of an elevator falling freely under Earth's gravity, its cable having been snapped.

What do I see?

If the gravity of Earth were uniform, the sphere with its oil film would fall freely down.

The film of oil would cover the sphere uniformly, gravity having disappeared (due to the weightlessness in the elevator). 

But the gravity of the Earth is NOT uniform. 

It obeys the inverse square law.

So the downward gravity at the bottom of the sphere (being closer to the Earth) would be slightly greater than the downward gravity at the center of the sphere.

And the downward gravity at the top of the sphere would be slightly lesser than the downward gravity at the center of the sphere.

RELATIVE to the center of the sphere (i.e. as felt by the sphere),  there is a slight resultant gravitational force downwards at the bottom of the sphere; and a slight resultant gravitational force upwards at the top of the sphere. 

It is simply a matter of subtraction of two collinear vectors.

In other words the film of oil at the bottom of the sphere is pulled down at the bottom and pulled up at the top.

The oil at the bottom leads and the oil at the top lags compared to the center of the sphere. 

So there is a piling up (bulge) of oil at both the bottom and the top of the sphere.

So there is a high tide at the bottom and a high tide at the top.

What about the oil film at the level of the center of the sphere?

The oil having flowed away both towards the bottom and towards the top, there is a thinning down at that site...in a first approximation.

So there is a low tide of oil there.

Hence Proved! QED!

In other words, it is not gravity but the gradient of gravity that causes tides.

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Let us now revert to our Earth, and the seas that cover it like a thin film.

For the moment let us ignore the Moon (an unpardonable sin).

And consider the Earth and the Sun. 

Earth is freely falling towards the Sun (like that sphere in an elevator with a broken cable).

So at the areas facing towards the Sun, Earth sees a high tide of seas.

Also a high tide at the areas facing away from the Sun. 

And low tides at the areas in between (equatorial).

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So also the tides due to the Moon.

Seen from the Moon, Earth is rotating around it (at the period of nearly 28 days).

So Earth is freely falling towards the Moon as well.

So at the areas facing towards the Moon, Earth sees a high tide of seas.

Also a high tide at the areas facing away from the Moon. 

And low tides at the areas in between (equatorial).

So the high tides are truly high on a New Moon Day as well as a Full Moon day.

Because, the high tides due to the Sun and the Moon assist each other, Moon and the Sun being in a near straight line.

And very low tides in between.

These are called the Spring Tides (nothing to do with the spring season...more like the spring in a shock absorber of a Chetak scooter).

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In reality, however,  the tides due to the Moon are larger than the tides due to the Sun.

Although the Moon is so much smaller than the Sun, it is so much closer to the Earth than the Sun is.

If the Sun were imagined to come in to reside at the site of our Moon, the Moon would be like our Aamne-Saamne neighbor (on a scale).

Merey saamne waali khidki mien ek chand ka tukda rehta hai

So the gradient of Moon's gravity is larger than the gradient of Sun's gravity.

Take now the Ashtami Day (shukla or bahula).

The Sun and the Moon are perpendicular to each other as seen by the Earth.

So the high tides due to them must cancel each other.

They do, to some extent.

But the tides due to the Moon, being larger than the tides due to the Sun, they overcome them.

So there are high tides on Ashtamis as well.

But these are not as great as those at the Poornima and Amaavaasya.

These are called Neap Tides ('neap' meaning powerless).

Sitting on that blessed rock near the Scandal Point on the Vizagh beach, I would therefore see 4 tides every lunar month (two spring tides and two neap tides) on Amaavaasya, Shukla Ashtami, Poornima, and Bahula Ashtami.

And since my Earth and I are spinning around themselves once in 24 hours, I would see these high and low tides repeating every 6 hours.

Phew!

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To be Continued

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శంకరార్పణం - 3688

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శంకరాభరణం సమస్య - 3688

“పురుషశ్రేష్ఠుఁడు సీరఁ గట్టి ముడిచెం బూమాల శీర్షంబునన్”

పరువుల్ బెట్టుచు చేరగన్ ప్రజలహో బ్రహ్మాండమౌ రీతినిన్

స్థిరమౌ తీరున కూచిపూడి కడనున్ సింగారి వేషమ్మునన్

వరమౌ నాటక మందునన్ మురియుచున్ భామా కలాపంబునన్

పురుషశ్రేష్ఠుఁడు సీరఁ గట్టి ముడిచెం బూమాల శీర్షంబునన్

(కంది శంకరయ్య గారి సౌజన్యంతో)

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Tides - 6

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Although he didn't ask me for a Testimonial, I have no hesitation in saying "Newton is a Genius".

Thirty years ago I happened to read Stephen Hawking's book: "A Brief History of Time"

At the end of that book were 3 Appendixes, each with a photo and a short biographical sketch. 

These three all-time Geniuses (according to Hawking)  were:

1. Galileo 

2. Newton

3. Einstein

Obviously Hawking was being modest...he had implied that the next in the line was:

4. Stephen Hawking :)

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London in the 17th Century was hit by a plague (like Mumbai is now). And Newton fled to his village home with an orchard that had apple trees. And he was sitting under one of those trees, contemplating, like I was at Harry's often at IIT KGP (and getting hit by crows' shit).

And an apple got detached from its branch and fell down (many say on Newton's head...not true).

As Newton watched it he is reputed to have exclaimed:

"Aha! Gravity!"

Even little Ishani could have said it.

Newton, on the other hand, looked up and saw the disk of a pale moon.

And realized that Moon also was in free fall towards the Earth like that apple.

That is GENIUS!

Moon in Free Fall towards the Earth?

Question: Why doesn't it fall down like a meteor or an asteroid and hit the Earth?

Answer: Inertia (First Law of Newton).

Moon was given a tangential velocity round the Earth in its time.

There are three theories of Moon's relation with Earth:

1. Daughter:

A bit of Earth got detached from Earth and flew away 

2. Sister:

Both Earth and Moon were born about the same time

3. Spouse:

Moon was wandering and found herself close to the Earth and got sucked into a nearly circular orbit

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'Inertia' was the toughest for us to understand at our university.

1. Suppose a bird perched on a tree sees a worm on the ground. And jumps vertically down to catch the poor worm.

But Earth is spinning. A simple calculation shows that in the time the bird takes to descend, the Earth, the tree, and the worm would have gone forward about 30 feet. 

And the bird ought to miss her worm by about 30 feet.

But she doesn't ever...she always catches her worm

2. You don't have to travel all the way to New York by a Pan Am flight.

Just go vertically up in a helicopter and stay there hovering. And eventually, since Earth is spinning, New York would come right under your nose.

And then descend.

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Newton also gave a 'thought experiment' to show how Moon is always in free fall around the Earth but never falls down on the earth smashing us.

Take a cricket ball and throw it horizontally. 

It would be in free fall and would take a parabolic trajectory and fall on the Earth about 30 feet away from you (horizontal range).

Throw the ball with increasing speeds. Its range will keep increasing.

Throw it harder and harder.

It will fall 30 miles from you.

But, wait...Earth is not flat. It is curved, and the 'horizon' is only about a few miles away.

So, as the cricket ball tries to fall on the ground, the ground itself would evade it by bending.

The ball keeps on trying and trying and fails to drop on the ground.

Eventually the cricket ball would go round and round the Earth in an elliptical orbit (and would hit your back if you were not anticipating it).

You have launched an 'artificial satellite'!

Moon, likewise, became the 'natural satellite' of the Earth long long ago.

It is always trying to fall on the Earth but always misses it (by about 384,400 km...the radius of the Moon's orbit).

Don't throw your cricket ball any faster...it will escape into space once for all.

Rahul Gandhi (the fifth Genius) promised his voters that he would throw away their poverty at an 'escape velocity'.

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Once Newton realized that both his apple and the Moon are in free fall due to the same Earth's gravity, he came up with his famous 'inverse square law".

Even I could have discovered it...just a cooking up (కిట్టింపు).

All it required was taking a ratio.

He didn't need the mass of the Earth, the mass of the apple, the mass of the Moon, or even the value of his famous "Universal Gravitational Constant".

All of them cancel away.

All he needed was to time the apple's fall (Galileo had invented the principle of the pendulum clock), height of the tree, the 'height' of the Moon, and the time period of rotation of the Moon.

Of course he needed  an expression for the 'centripetal acceleration'.

That required Calculus.

And he invented it!

Genius!

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The first precise value of 'Newton's Universal Gravitational Constant' came a century after Newton.

It was measured by Henry Cavendish in a lab he constructed in his home.

That home-lab was terribly expensive.

Q: Where from did Cavendish (and other English Scientists) get their money for their costly experiments and explorations (geological mostly)?

A: A rogue called Robert Clive gave it to them.

...All of them had shares in a profitable thievery called the  "East India Company"

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To be continued

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శంకరార్పణం - 3687

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శంకరాభరణం సమస్య - 3687

“తేలును ముద్దులాడు బడతిం గని మెచ్చఁ దగున్ ముదమ్మునన్”

జాలిగ కోపమున్ విడిచి చక్కగ నవ్వుచు నాథునిన్ గనన్

పూలను దాల్చుచున్ జడను పొంకము మీరగ కౌగిలించుచున్

మేలుగ పచ్చ రూపమున మెల్లగ గాంచుచు ఛాతి మీదదౌ 

తేలును ముద్దులాడు బడతిం గని మెచ్చఁ దగున్ ముదమ్మునన్

పచ్చ = tattoo

(కంది శంకరయ్య గారి సౌజన్యంతో)

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Tides - 5

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"This is because tides in our seas are due to an interplay of the combined gravities of the Moon and the Sun.

In a sense they are the highly visible terrestrial events due to celestial bodies."

This is great!

"High tide and low tide occur twice a day one followed by the other about six hours apart.

Thus there are two high tides and two low tides alternating every day."

Oh! No! That is terrible!

Why so ?

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It is like this:

Suppose I am sitting on the rock on the beach of Vizagh, with the Bay of Bengal giving me company.

And it is midday on a New Moon Day (అమావాస్య; Amaavaasya).

Then the Sun and the Moon are aligned with each other more or less in a straight line above my head. Their gravitational forces on me and the sea are assisting each other pulling us towards them. My rock and I are fairly rigid bodies attached to the earth and do not tear us away towards the Sun and the Moon so easily...

But not so the sea water which is a fluid that can flow. So the sea water accumulates towards the Sun and the Moon and there is a bulge in the sea level. And the sea floods the beach. 

We have a high tide. 

Fine!

About 12 hours later, at my midnight, the Sun and the Moon have rotated (as I see them) and are almost overhead at a point on the other side of the Earth (antipode) where it is midday.

So there must be a bulge (and a high tide) there, and, since the sea by my rock is pulled away there flowing towards my antipode, my sea level must have a shrink (low tide).

But this is not what happens in practice:

My sea bulges again and we have another high tide although the Sun and the Moon are nowhere to be seen by us...they being above my antipode.

How come?

Strange!

That is not all...

Suppose my rock and my sea and I are sitting at midday on a Full Moon Day (పూర్ణిమ) when the Sun and the Moon are roughly opposite to one another...with the Sun on my head and the Moon on the head of my antipode.

I would expect then that their gravitational pulls of the sea by my side try to cancel each other to some extent; and my antipode as well as I should have a low tide.

But that is not what happens!

Both of us have high tides again (like on the New Moon Day).

How does one explain these anomalous tides?

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First of all we should note that none of the heavenly bodies is nailed to the heaven. All of them are free to move. And their motions are governed by the gravitation at their site (local).

Apart from gravity, their motions are not influenced by other forces...so Celestial Mechanics is simple :)

99% of their motions can be explained by Newtonian Mechanics and Newtonian Gravity (no need to invoke Einstein's Mechanics and Einstein's Gravity...except near blackholes).

Moon rotates around the Earth captured by it. Earth and other planets (along with their satellites) rotate around the Sun. Sun with  its extended family rotates around our Milky Way Galaxy. And our Galaxy rotates around other galaxies. And all galaxies slowly move by and large away from others (Expansion of the Universe).

All bodies that move only under gravity are said to be "freely falling".

Fortunately most of us on our Mother Earth do not experience free fall.

It was only in my Muthukur school days that I was jumping down for a fraction of a second from a low-hanging branch of a tree playing "Monkey Business".

The apple that fell down from its tree (Newton) is under free fall, ignoring air friction. 

The youth who springs from the diving board into his swimming pool is under free fall (Einstein).

The passengers in the lift undergo free fall if the cable of their lift suddenly snaps.

And the ditched lover jumping from the balcony of his 13th floor flat is under free fall.

Free falls never hurt anyone....it is the landings that do it.

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On the other hand, in our Earthly Mechanics, Gravity is just one of the forces. 

The bob of a simple pendulum moves under gravity plus tension.

The block on the inclined plane moves under gravity plus normal reaction plus friction.

There are no tensions and normal reactions in the heavens.

Indeed as I progressed from my first year to the final year labs in our university, gravity ceased to matter much at all.

It was only in our first year lab that we had Borda's Pendulum, Compound Pendulum, Kater's Pendulum, cantilevers loaded in the center or sides, and the viscometer which had weights falling under gravity plus viscous friction.

In the second year, we moved to Heat...Copper Voltameter, Stefan's Constant, Newton's law of Cooling, Planck's Constant etc, ignoring gravity altogether.

And then on to the Electricity Lab...Wheatstone's Bridge, Rayleigh's Bridge, Anderson's Bridge, Potentiometer etc

And then on to Optics...Newton's Rings, Fresnel Biprism, Lloyd's Mirror, Straight Edge Pattern etc.

And then on to Electronics...Amplifiers, Oscillators, Modulators, Demodulators, Superhet Receiver etc..

...None of which required Gravity...unlike our Celestial Mechanics in which we can  forget all these devils...

We the experimenters (trying to cheat) and the apparatus on its table  (trying to misbehave) were firmly grounded by the Normal Reaction and Friction....

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To be continued

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