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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