i know the mainstream view "gravity tides" but that would sugest that the high tide points at the moon, and i don't think it does. the only other thing it could be is the earth moving with the barycentre wobble. as someone put it "the wobble sloshes the sea around"

There is a website associated with this board!

__________________
Everything I need to know I learned through Googling.

There is also a lengthy thread here on the tides.

In short, tides are caused by differential gravitational forces. The moon pulls on the closer side more because, well, it's closer.

thanks for that. in the java applet, the moon was directly above the high tide. i don't think that is right. the moon is nearer above low tide.
this is what i mean, mainstream " gravity causes tides". i too, have heard this but i'm just saying "maybe not". and a lot of people seem offended because the've learnt differently. it's only supposed to be thought provocking

What do you mean the moon is "nearer" above low tide. It's not like the moon comes swooping down near earth and then jumps back up into the sky. High tides are "above" the moon because that is where the greatest graviational attraction is.

http://csep10.phys.utk.edu/astr161/lect/time/tides.html

__________________
"The bread's hollowed out --- the veggies go on forever --- and --- oh my God! --- it's full of meat!" - Maksutov

in the java applet, the moon was directly above the high tide. i don't think that is right. the moon is nearer above low tide.

That's because the Moon is going round the earth every twenty-eight days, but the Earth is spinning every twenty-four hours. The tidal bulge created by the pull of the Moon's gravity is pulled ahead of the Moon by the Earth's rotation, hence the Moon does not lie exactly over the high tide but rather lags behind.

This is slowing the Earth's rotation (the bulge is being dragged by the Moon), and causing the Moon to recede (the bulge is also dragging the Moon, pulling it forward and into a slightly higher orbit). Eventually this will result in the entire system becoming locked so that one side of Earth always faces the Moon as well as one side of the Moon always facing Earth. This situation has already occurred in the Pluto/Charon system.

__________________
"The very powerful and the very stupid have one thing in common: They don't alter their views to fit the facts, they alter the facts to fit their views." The Doctor, Doctor Who: The Face of Evil.

[quote="Jason Thompson
The tidal bulge created by the pull of the Moon's gravity is pulled ahead of the Moon by the Earth's rotation, hence the Moon does not lie exactly over the high tide but rather lags behind.[/quote]

so the common theory sujests the moon being over the high tide but allows room for this not being the case. or maybe the theory is wrong.

Maybe, but that's a really huge maybe.

Imagine you're holding a garden hose, that has a steady stream of water coming out of it with enough pressure to push it out a few feet if the hose is horizontal. You move like a top spinning, and the stream bends. Now, all that water is still going straight out from you, but because you moved the stream is curved. The "end" of the stream needs time to catch up to the "beginning" (the hose end). That's a bit like what Jason Thompson meant when he said:

__________________
h00!

so the common theory sujests the moon being over the high tide but allows room for this not being the case.

No, the common theory says that the Moon pulls on the Earth creating the tidal bulge and this bulge is carried ahead of the Moon by the Earth's faster rotation. It makes perfect sense, and fits with observation.

__________________
"The very powerful and the very stupid have one thing in common: They don't alter their views to fit the facts, they alter the facts to fit their views." The Doctor, Doctor Who: The Face of Evil.

The common theory works just fine, its just simplified in that java animation. The actual motion of the tides at any location on earth is highly complex and includes things like water depth and shore geometry.

You are making something out of nothing.

(shameless plug)

... or you could go out and buy a copy of "Bad Astronomy" since it's now in its final printing (if you haven't already done so), and read chapter 7.

__________________
CAMERON: The 1961 Ferrari 250GT California. Less than a hundred were made. My father spent three years restoring this car. It is his love, it is his passion.
FERRIS: It is his fault he didn't lock the garage.

Good point. Surprisingly, I haven't bought the book. I read a lot, but most books are from the library. Sorry BA. :P

You have to factor in the mass and density of the earth, verses then mass of the ocean - since the the earth is also tugged toward the moon, the ocean on the other side is left behind - hence the higher tide near the opposite side...of course, the rotations of the earth and moon come into play too, and the position of the sun, but when the dust is all settled, the mechanics work out almost perfectly with newtonian predictions...

__________________
jwj

If you always believe what you already know, you can't learn anything - Liz

Anyone wanta talk wave resonance for tidal height variations?

Also, what would happen to the Moon's orbit if it and Earth were perfect isotropic spheroids and inelastic? Would energy be exchanged? [assume current rotation and orbital speeds]

I suppose "frame dragging" would count. #-o

__________________
Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

you said.........the mechanics work out almost perfectly with newtonian predictions..... (how do you do all that bordering????) but newton also said "two bodies don't fell gravity from each other if they are falling at each other" which is roughly whats happening with the earth and moon. the moon moves all the way round the earth and the earth moves around the barycentre.

Wait a sec. The Earth-moon barrycenter is within the earth. [Link, additionally if you've ever wanted to know more than pi=3.14 you'll see it here]

So, you're saying the earth moving around the barrycenter causes the oceans to 'slosh' and thus the tides. However, if the point of rotation is within the earth, then over then years friction with the ocean beds would have dampened the 'sloshing' to a stop. Then following though the logic you seem to be presenting, all the water would have been pulled by centrifugal force to the fartherest point from the center of rotation. Thus the side closest to the barrycenter would be at a perpetual low tide (if not completely dry) and the point fartherest away would be at perpetual high tide. Considering the age of the earth, I'd say enough time has passed that this would have either happened by now or it'd be very obivous it was headed that way.

The earth and moon aren't point particles and therefore, they feel tidal forces. Newton's laws do predict that. The fact that a cc of water on the near-side of the earth is closer to the moon than one on the far side means it feels more gravitational force. The difference is the tidal force.

From that website:
Another miracle of pi?

From its tides page:
It's actually about three times that.
Many magnitudes less than that.
The only tide page I've seen with as bad an explanation was NOAA's.
Not every day. Every century.
The moon's "most massive side" does not face the Earth directly.

I didn't check it out too much, just wanted someplace that mentioned where the barrycenter was. Shoulda looked a bit harder.

Sorry I looked into it! I've done the same thing.