Two High Tides - Page 2

Mothy · Mothy's Garage

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

sketchers356 · 11-07-2008, 05:34 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, 05:46 AM

Quote:

Originally Posted by Pazuzu

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, 05:53 AM

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

ckissick · 11-07-2008, 06:16 AM

Quote:

Originally Posted by sketchers356

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.

sketchers356 · 11-07-2008, 06:24 AM

Quote:

Originally Posted by ckissick

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.

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

BRPORSCHE · 11-07-2008, 06:29 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, 06:38 AM

Quote:

Originally Posted by sketchers356

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

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

DARISC · 11-07-2008, 06:52 AM

Quote:

Originally Posted by sketchers356

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, 06:58 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, 07:00 AM

It's all Poseidon's fault!

M.D. Holloway · 11-07-2008, 07:05 AM

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

sketchers356 · 11-07-2008, 07:17 AM

Quote:

Originally Posted by LubeMaster77

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

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

DARISC · 11-07-2008, 07:21 AM

Quote:

Originally Posted by scottmandue

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, 07:54 AM

Quote:

Originally Posted by sketchers356

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

Or it could be an invisible concentration of cosmological constants.

DARISC · 11-07-2008, 08:03 AM

Quote:

Originally Posted by ckissick

Or it could be an invisible concentration of cosmological constants.

Finally. An explanation that makes sense.

scottmandue · 11-07-2008, 08:59 AM

Quote:

Originally Posted by DARISC

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, 09:59 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, 10:10 AM

Quote:

Originally Posted by Pazuzu

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, 02:16 PM

Quote:

Originally Posted by Pazuzu

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.