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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