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-   -   Two High Tides (http://forums.pelicanparts.com/off-topic-discussions/439760-two-high-tides.html)

Mothy 11-07-2008 04:29 AM

Oh dear - what did I start here......

sketchers356 11-07-2008 06:34 AM

Another Physicist here.

An easier way to think of it is to do the vector sum of the earth's gravitational field and the moon's gravitational field.

sketchers356 11-07-2008 06:46 AM

Quote:

Originally Posted by Pazuzu (Post 4287379)
I'm a physicist, and as much as I hate to say it...you're wrong. Sorry.

The term "tidal" and "tide" come from gravitational tidal forces. Any gravitational source puts several different stresses on any other object...it doesn't just pull it.

One of the forces is a squeezing in the transverse direction. Another is a lengthening in the radial direction. These two force together cause the ocean to form an oval (more properly, and ellipse) around the Earth (which is also being squeezed and lengthened into an ellipse, but on a MUCH smaller scale).

The math behind it is pretty complex, but the result is well understood. It's not because of an ancient stable tidal wave traveling around the planet.

What does he say that is wrong? All that he is saying is that the tides are a result of forces that started long ago it seems to me. This is correct. He simply does not understand the more basic underpinnings of what those forces are.

I dont think that the Mathematics are THAT complex. Just do a MacLaurin expansion about the center of mass of the earth/moon system. The first term is the traditional gravitational force. The rest of the terms are the tidal terms, with the highest order term being the one that we are more familiar with.

BRPORSCHE 11-07-2008 06:53 AM

There go the physicist's getting all wordy...

ckissick 11-07-2008 07:16 AM

Quote:

Originally Posted by sketchers356 (Post 4288096)
He simply does not understand the more basic underpinnings of what those forces are.

Man, those physics geeks are starting to pi$$ me off. It all started in college at the UCSB geology department's Friday keggers on the roof of our two-story building. While we were getting tanked, the physics nerds across the way would launch water ballons at us with their trebuchet.

Curses, physicists! Your mother was a hamster, and your father smelt of elderberry.

http://forums.pelicanparts.com/uploa...1226070950.jpg

sketchers356 11-07-2008 07:24 AM

Quote:

Originally Posted by ckissick (Post 4288181)
Man, those physics geeks are starting to pi$$ me off. It all started in college at the UCSB geology department's Friday keggers on the roof of our two-story building. While we were getting tanked, the physics nerds across the way would launch water ballons at us with their trebuchet.

Curses, physicists! Your mother was a hamster, and your father smelt of elderberry.

http://forums.pelicanparts.com/uploa...1226070950.jpg

Hey, I was trying to cut you some slack man!

BRPORSCHE 11-07-2008 07:29 AM

I know exactly how the man feels. My dad is a physicist and I am a geology major. Constant battles.

ckissick 11-07-2008 07:38 AM

Quote:

Originally Posted by sketchers356 (Post 4288201)
Hey, I was trying to cut you some slack man!

You're very kind. Thank you. (elderberry breath)

DARISC 11-07-2008 07:52 AM

Quote:

Originally Posted by sketchers356 (Post 4288067)
Another Physicist here.

An easier way to think of it is to do the vector sum of the earth's gravitational field and the moon's gravitational field.

You physicists are all alike. You get asked a difficult question and you play the vector sum card.

sketchers356 11-07-2008 07:58 AM

Note that I also played the expansion card.

Now if I can only play the SHO card then I have a set!

scottmandue 11-07-2008 08:00 AM

It's all Poseidon's fault!

M.D. Holloway 11-07-2008 08:05 AM

maybe there are two moons - one you see and one you don't...

sketchers356 11-07-2008 08:17 AM

Quote:

Originally Posted by LubeMaster77 (Post 4288321)
maybe there are two moons - one you see and one you don't...

The dark matter hypothesis....I like it!

DARISC 11-07-2008 08:21 AM

Quote:

Originally Posted by scottmandue (Post 4288299)
It's all Poseidon's fault!

Right. Blame it on some old dead Greek guy.

Well, he may be long gone, but many still myth him.

ckissick 11-07-2008 08:54 AM

Quote:

Originally Posted by sketchers356 (Post 4288354)
The dark matter hypothesis....I like it!

Or it could be an invisible concentration of cosmological constants.

DARISC 11-07-2008 09:03 AM

Quote:

Originally Posted by ckissick (Post 4288440)
Or it could be an invisible concentration of cosmological constants.

Finally. An explanation that makes sense.

scottmandue 11-07-2008 09:59 AM

Quote:

Originally Posted by DARISC (Post 4288365)
Right. Blame it on some old dead Greek guy.

Hey now... Posie is doing just fine... we had a couple of beers just the other day... I had to leave thought, after a few drinks he starts waving his trident around and trying to grab my a$$.

Pazuzu 11-07-2008 10:59 AM

Didn't realize I was going to start such an issue here. I take it back ,it's a giant stable wave that been rotating around the Earth for billions of years, and has a wavelength equal to half the circumference of the Earth. If the Moon stopped orbiting, that wave would continue around the planet at the same rate, slowly loosing amplitude until it disappeared.

DARISC 11-07-2008 11:10 AM

Quote:

Originally Posted by Pazuzu (Post 4288762)
Didn't realize I was going to start such an issue here. I take it back ,it's a giant stable wave that been rotating around the Earth for billions of years, and has a wavelength equal to half the circumference of the Earth. If the Moon stopped orbiting, that wave would continue around the planet at the same rate, slowly loosing amplitude until it disappeared.

I doubt that anyone would care much if the moon stopped orbiting, but I bet there'd be a flood of complaints if the amplitude got lost.

ckissick 11-07-2008 03:16 PM

Quote:

Originally Posted by Pazuzu (Post 4288762)
Didn't realize I was going to start such an issue here. I take it back ,it's a giant stable wave that been rotating around the Earth for billions of years, and has a wavelength equal to half the circumference of the Earth. If the Moon stopped orbiting, that wave would continue around the planet at the same rate, slowly loosing amplitude until it disappeared.

I found my old text book on oceanography, and found this: "Tides are the longest waves oceanographers commonly deal with, having a period of 12 hours and 25 minutes, and a wave length of half the circumference of the earth. The crest and trough of the wave are the high tide and low tide, respectively."

Also: "The high tide does not occur directly below the moon, but is slightly ahead of it. This positioning is the result of the friction of the earth as it rotates beneath the water. The rough-bottomed ocean basins tend to drag the 'bulges' along, while the gravitational effect of the moon wants to hold the bulge beneath it. The result is a compromise position, somewhere in between, at which these two forces are at equilibrium."

If the moon were to go away, the tides would still be with us, but they would be much smaller tides caused by the gravity of the sun.


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