What if the Earth would have spin around itself twice as it's speed?

[essenmein]

This is a statement about rock. It goes up at the equator and down at the poles, the total volume is conserved. It would lead to considerable earthquakes if it happens quickly.

On a large scale all of Earth is like a liquid.

It was a general statement about conservation of volume. For this deformation to happen, whether rock, or water, the materials must flow. My only point that I have fruitlessly been trying to make, is that water flows much more easily than rock, so it would respond to much lower forces and do so much more quickly than rock.

 

[DrStupid]

For this deformation to happen, whether rock, or water, the materials must flow.

Nothing needs to flow for a deformation of 0.3 %.

My only point that I have fruitlessly been trying to make, is that water flows much more easily than rock, so it would respond to much lower forces and do so much more quickly than rock.

And my point that I have fruitlessly been trying to make, is that the rock already responds as quickly as the water to the tidal forces of Moon and Sun. You need to explain why you expect it to response significantly slower in the case of a loss of centrifugal forces - so slowly that it takes more time for the rock to lift some km up or down, than for the water to flow thousands of km from the aequator around the Earth to the poles.

 

[essenmein]

Nothing needs to flow for a deformation of 0.3 %.

If volume is conserved, you would have about 0.3% flow other wise deformation has not happened.

And my point that I have fruitlessly been trying to make, is that the rock already responds as quickly as the water to the tidal forces of Moon and Sun. You need to explain why you expect it to response significantly slower in the case of a loss of centrifugal forces - so slowly that it takes more time for the rock to lift some km up or down, than for the water to flow thousands of km from the aequator around the Earth to the poles.

My last addition to this thread will be the concept of viscosity.

From the wiki:
"Conversely, many "solids" (even granite) will flow like liquids, albeit very slowly, even under arbitrarily small stress "

But this is the science fiction forum, so if you want to have water flow slower than rock that's up to you.

 

[DrStupid]

If volume is conserved, you would have about 0.3% flow other wise deformation has not happened.

The conservation of volume doesn't need any flow. Compression, bending and stretching in a very small scale would be sufficient. However, there might be flow involved, but not in solid rock but in the liquid outer core and the semi-liquid outer mantle and also in a very small scale. And again, we know that this is possible because it already happens with a period of 12 hours.

But this is the science fiction forum, so if you want to have water flow slower than rock that's up to you.

You are talkin about flowing rocks, not me.

 

[jim mcnamara]

I want to see citations posted that support these positions. Or we will have to close the thread. Any questions? Please the forum rules. Thank you.

Whenever you make what are meant to be taken to be real world statements you have to back them up, even here in the wishful thinking forum. If you specifically posit that we want rocks to flow (or not) and who cares if it matches the real word, then go for it. But that is not what I see.

 

[jim mcnamara]

Also note that the question maker has not logged back on since the original post, Aug 25, to see what we discussed here. ...If that matters to you.

 

[DrStupid]

I want to see citations posted that support these positions.

OK, here is a citation for the Earth tides: https://link.springer.com/article/10.1007/BF01449116

It says that "[...] Earth is anything but an ideal body it does change its shape, with radial deformations reaching 0.5 metres."

This source provides a detailed theoretical description of this effect: https://books.google.de/books?hl=de&lr=&id=SIHNCgAAQBAJ&oi=fnd&pg=PA163#v=onepage&q&f=false

The rough estimation of the tidal potential in chapert 6.2.1 results in an elevation of the geoid of around 0.36 m by the Moon and 0.16 m by the Sun. This corresponds perfectly with the 0.5 meters mentioned by P. Melchior above. That means that there is no significant resistance to the tidal forces.

The second source by D.C. Angnew also includes anelastic effects. But they appar to be so small compared to the elastic effects that there is no reason to speculate about flow or something similar. Earth can be assumed to be a solid body with very low Young modulus.

Of course an increase of the deformation from 21 km to about 85 km (according to my estimation for a 12 h rotation) is several orders of magnitude above the 0.5 meters of the Earth tides. But so are the forces under the mountains on the poles. The pressure would be in the range of GPa. Claiming that the resulting deformations would take significiantly longer than the Earth tides requires proper justification.

 

[essenmein]

I took data from the opposite case, which I'm sure you'll agree is analogous. What if the Earth stopped spinning.

This is not the first time people have talked about this, its even been modeled. All the references re this Earth stopping business place geological adjustments in the millions of years kind of range, and the oceanic adjustments in the range of days or weeks.

"This bulge in the ‘solid’ Earth took billions of years to slowly develop. This is because the solid matter moved only very slowly in response to the outward force caused by the spin of the planet.But the liquid water in the oceans is far more mobile and responsive to forces."

I mean its intuitively obvious.

https://www.esri.com/news/arcuser/0610/nospin.html
https://www.australiangeographic.co...ppen-if-our-planet-stopped-spinning-entirely/

 

[DrStupid]

"This bulge in the ‘solid’ Earth took billions of years to slowly develop. This is because the solid matter moved only very slowly in response to the outward force caused by the spin of the planet.

That makes no sense. Why should the bulge have ever been smaller? The Earth was rapidly spinning from the beginning (or at least after the collision with Theia). It is much more likely the other way around. The Earth has been formed with a much larger bulge because the rotation was much faster. Than it took billions of years to decrease it to the current size - not because the solid matter moved only very slowly but because the rotation decreased so slowly.

If Earth would be suddenly stopped and than released, I expect it to oscillate with the spherical mode ₀S₂ which has a period of 54 minutes (according to http://www.geo.uu.nl/~paulssen/ISS/iss14.pdf) until the energy has been dissipated (mainly due to the motion of water on the surface). That would be too fast for the water to follow, unless it is moving with supersonic speed.

 

[essenmein]

That makes no sense. Why should the bulge have ever been smaller? The Earth was rapidly spinning from the beginning (or at least after the collision with Theia). It is much more likely the other way around. The Earth has been formed with a much larger bulge because the rotation was much faster. Than it took billions of years to decrease it to the current size - not because the solid matter moved only very slowly but because the rotation decreased so slowly.

If Earth would be suddenly stopped and than released, I expect it to oscillate with the spherical mode ₀S₂ which has a period of 54 minutes (according to http://www.geo.uu.nl/~paulssen/ISS/iss14.pdf) until the energy has been dissipated (mainly due to the motion of water on the surface). That would be too fast for the water to follow, unless it is moving with supersonic speed.

At the end of the day I'm not a geologist, and that's a reasonable question. I can only say geology based sources I've read re Earth stopping have said the bulge in the rock is responding much slower than the ocean. The resonance thing I can imagine doesn't really come into play unless it is triggered by a sufficiently short impulse. If the Earth stopped fast enough to excite a 54min period osculation, I would imagine everything would get decimated by the oceans and the atmosphere continuing to rotate.

 

[DrStupid]

The resonance thing I can imagine doesn't really come into play unless it is triggered by a sufficiently short impulse.

Suddenly stopping and than releasing the Earth would be such an impulse. If the rotation changes slower, I would expect an oscillation with smaller amplitude around the changing geoid. For sufficiently slow changes there would be no oscillation and the Earth always fits the geoid.

If the Earth stopped fast enough to excite a 54min period osculation, I would imagine everything would get decimated by the oceans and the atmosphere continuing to rotate.

I assumed oceans and atmosphere to be part of the Earth and therefore to be stopped too. If we allow water and air to remain rotating, than we could do that for the liquid outer core as well (just as an example). That would result in a lot of new possible scenarios - all of them even more off-topic than the sudden change of the rotation of Earth as a whole.