Seperating Atlantis from reality

originally posted by: bloodymarvelous

originally posted by: Harte
a reply to: bloodymarvelous
The Moon provides the dampening.
It's a small wobble for a short time.

The Moon is what causes the axis to always have an axial tilt between 22 and 24 degrees. Because it is based on the Moon's orbit, it doesn't change much over time.

en.wikipedia.org...

As your own link states, the Earth's tilt is stabilized by the Moon. Without it, the tilt could change very rapidly (in geological time.)

originally posted by: bloodymarvelous

The masses involved are laughably larger than the largest iceberg imaginable.
The entire mass of Arctic ice could shift to the equator with no long lasting impact on the Earth's spin.

The weather would suck though.

Harte

We're not talking about a change in rotational center of mass if that happened, though. Moving mass from South to North is different than moving it from East to West.

You can think of a spinning spheroid as a large number of discs, all stacked on top of each other. Those discs need to be symmetric. If one isn't, then another one needs to be asymmetric in a way that balances it.

If a lump of mass located as say............. 90 degrees East, gets removed from the spheroid (say it vanishes). Then an equal and opposite amount of mass needs to disappear at 90 degrees West. Otherwise we've lost East/West symmetry. (North /South Symmetry doesn't matter. You can spin a cone just as easily as a spheroid.)

The center of mass is in a new place now, and the spinning body will compensate by beginning to spin around that center of mass instead. However, it will still have some left over rotational inertia from its previous configuration.

What you're saying is that you cannot see that the redistribution of water would easily maintain the current center of mass.
Truth is, the isostatic rebound of the crust under the (former) ice would have a greater impact, and could cause the Earth's rotation to slow by a picosecond or two.

Harte

originally posted by: Harte

originally posted by: bloodymarvelous

originally posted by: Harte
a reply to: bloodymarvelous
The Moon provides the dampening.
It's a small wobble for a short time.

The Moon is what causes the axis to always have an axial tilt between 22 and 24 degrees. Because it is based on the Moon's orbit, it doesn't change much over time.

en.wikipedia.org...

As your own link states, the Earth's tilt is stabilized by the Moon. Without it, the tilt could change very rapidly (in geological time.)

The point I've been trying to make is that the lunar tide actually isn't all that strong of an effect. Only about 0.7 meters of lift. And it applies to both sides of the planet simultaneously.

But since the Earth has no other stronger forces acting upon it, that small effect eventually reels it in over time.

It's not a question of a force being strong relative to the total inertial mass of the planet. A small force, acting over a long enough time can change its momentum.


Compared to the tide, the melting of a glacier over 3 km tall spread out over a sufficiently wide area, would be much stronger. And it would be asymmetric, not happening on both sides of the planet at the same time.

(It wasn't 10 miles like I was thinking, just 2 miles.)

originally posted by: bloodymarvelous

The masses involved are laughably larger than the largest iceberg imaginable.
The entire mass of Arctic ice could shift to the equator with no long lasting impact on the Earth's spin.

The weather would suck though.

Harte

We're not talking about a change in rotational center of mass if that happened, though. Moving mass from South to North is different than moving it from East to West.

You can think of a spinning spheroid as a large number of discs, all stacked on top of each other. Those discs need to be symmetric. If one isn't, then another one needs to be asymmetric in a way that balances it.

If a lump of mass located as say............. 90 degrees East, gets removed from the spheroid (say it vanishes). Then an equal and opposite amount of mass needs to disappear at 90 degrees West. Otherwise we've lost East/West symmetry. (North /South Symmetry doesn't matter. You can spin a cone just as easily as a spheroid.)

The center of mass is in a new place now, and the spinning body will compensate by beginning to spin around that center of mass instead. However, it will still have some left over rotational inertia from its previous configuration.

What you're saying is that you cannot see that the redistribution of water would easily maintain the current center of mass.

People always make the mistake of thinking that a "1" is different than a "0" in physics. If I were talking about suddenly adding a giant glacier, then you might better understand how that would affect the symmetry. But because I'm talking about subtracting one, you're thinking it would make no difference because it's a subtraction rather than an addition.

Think about an ice skater pulling in their arms to accelerate a spin. The glacier melting and redistributing its mass to lower altitudes was that.

Except, it's more like if our skater had pulled in their right arm, but not their left.

Truth is, the isostatic rebound of the crust under the (former) ice would have a greater impact, and could cause the Earth's rotation to slow by a picosecond or two.

Harte

Maybe so. But if the change in rotation speed happens not at the equator, but at a higher latitude, and on only one side of the planet, then what direction will the change in rotation go?

Not the direction it should go.

It wouldn't just speed up or slow down in the direction it is already going. It would change direction.

Temporarily leaving the 22-24 degree tilt it is supposed to be at. Over time, the Moon would eventually correct this again, but if the planet has already traveled a considerable distance down the off-tilt path it won't turn around and undo that part. It will just stop going further.

a reply to: bloodymarvelous
You're still not understanding.
You're not subtracting the mass of a glacier. You're subtracting the form of a glacier.

The mass itself is evenly distributed around the globe as water.

I said it could cause a wobble. But not for a long time.
I didn't say the Moon would keep the Earth from wobbling in reaction to a huge event. I said it would dampen the wobble down over time into eventual nonexistence.

Remember, the earthquake in Chile (I think it was) happened on "one side of the Earth" as well, and caused the day to lose a tiny fraction of a second. With no resulting wobble.

Harte

originally posted by: Harte
a reply to: bloodymarvelous
You're still not understanding.
You're not subtracting the mass of a glacier. You're subtracting the form of a glacier.

The mass itself is evenly distributed around the globe as water.

Yes. Just like how when an ice skater pulls in their arms, they are not subtracting their arms. Just moving them.

Change in total mass means absolutely nothing at all.

Change in form is the only thing that matters here. So yes. I am discussing a change in form, and not a change in mass.

I said it could cause a wobble. But not for a long time.
I didn't say the Moon would keep the Earth from wobbling in reaction to a huge event. I said it would dampen the wobble down over time into eventual nonexistence.

Remember, the earthquake in Chile (I think it was) happened on "one side of the Earth" as well, and caused the day to lose a tiny fraction of a second. With no resulting wobble.

Harte

Yes. But the quake didn't change the shape of the landscape.

Suppose your arms are stretched out to the sides, extended like bird wings, and your center of mass is.... say at your sternum.

And then you pull your right arm in.

Now your center of mass is no longer located at your sternum.

If you were spinning when that happened, then your top/bottom center of mass matters too.

If your top/bottom center of mass were also at the height of your arms, you would keep spinning on the same axis as before, but with a different center (perhaps your left lung now.) - That is like melting a glacier located at the equator.


If your top/bottom center of mass were located at your pelvis, then in addition to moving the center of your spin to your left lung, you would also be tilting the axis of your spin so it was no longer oriented from your toes to your head, but at a diagonal angle. - That is like melting a glacier located above the equator.

- If an astronaut spinning horizontally in free space were to conduct this experiment, you would see him begin to rotate vertically as well as horizontally.

originally posted by: bloodymarvelous

originally posted by: Harte
a reply to: bloodymarvelous
You're still not understanding.
You're not subtracting the mass of a glacier. You're subtracting the form of a glacier.

The mass itself is evenly distributed around the globe as water.

Yes. Just like how when an ice skater pulls in their arms, they are not subtracting their arms. Just moving them.

Change in total mass means absolutely nothing at all.

Change in form is the only thing that matters here. So yes. I am discussing a change in form, and not a change in mass.

I said it could cause a wobble. But not for a long time.
I didn't say the Moon would keep the Earth from wobbling in reaction to a huge event. I said it would dampen the wobble down over time into eventual nonexistence.

Remember, the earthquake in Chile (I think it was) happened on "one side of the Earth" as well, and caused the day to lose a tiny fraction of a second. With no resulting wobble.

Harte

Yes. But the quake didn't change the shape of the landscape.

Suppose your arms are stretched out to the sides, extended like bird wings, and your center of mass is.... say at your sternum.

And then you pull your right arm in.

Now your center of mass is no longer located at your sternum.

If you were spinning when that happened, then your top/bottom center of mass matters too.

If your top/bottom center of mass were also at the height of your arms, you would keep spinning on the same axis as before, but with a different center (perhaps your left lung now.) - That is like melting a glacier located at the equator.


If your top/bottom center of mass were located at your pelvis, then in addition to moving the center of your spin to your left lung, you would also be tilting the axis of your spin so it was no longer oriented from your toes to your head, but at a diagonal angle. - That is like melting a glacier located above the equator.

- If an astronaut spinning horizontally in free space were to conduct this experiment, you would see him begin to rotate vertically as well as horizontally.

Whatever. This is more like an ice skater popping a zit on one side of their face.

Harte

a reply to: bloodymarvelous

Really appreciate your analysis, BlMa, btw. Thanks for posting.

Thanks. It's just one of many possibilities for our lost city of sea farers.


All we know for sure is that they were supposedly from outside the Pillars of Heracles, and apparently a separate continent from Europe and Africa.

Seems the Greeks didn't know much of anything about the world further beyond that point. Might as well have been outer space, from their perspective.

Can't really rule much out. Can't really rule anything in.

Maybe that's what makes Atlantis threads so much fun?