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

[Rosegoldtaken]

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

What would have be the consequences? How would has it affect the climate and living things?

 

[sophiecentaur]

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

What would have be the consequences? How would has it affect the climate and living things?

This reads like a homework assignment. So I ask you what are your views on the subject? You can expect some responses, once you have given some of your own input.

 

[Rosegoldtaken]

This reads like a homework assignment. So I ask you what are your views on the subject? You can expect some responses, once you have given some of your own input.

Firstly it is not a homework. My views about this;

The climate would have been different than the way it is today,

The equator's around would be under water,

Gravity would be less affect in equator,

We could see other side of the moon,

It is for a story that i write. I wanted to year different views.

 

[sophiecentaur]

Yes, that's better. I can now respond.

The equator's around would be under water,

Why? Some physics needed here.

We could see other side of the moon,

How? Are you talking about tidal locking being different? The Physics would suggest otherwise.
How do you think a faster day / night cycle could affect the temperatures at the surface? (I think the more subtle effects could be ignored in a simple treatment).

 

[Nugatory]

Gravity would be less affect in equator,

How large would this effect be? Would it even be noticeable?
(The point of this question is to get you to think about how you might calculate the effect)

 

[mfb]

The equator's around would be under water,

It wouldn't, or at least not more than today. The shape of Earth would be different, it would be even more oblate than it is today, and as result oceans and solid land can still exist everywhere.

We could see other side of the moon,

No. We can't see the other side because the rotation of the Moon matches its orbital period, this is independent of the rotation of Earth.

 

[pinball1970]

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

What would have be the consequences? How would has it affect the climate and living things?

The Biology on the planet would be completely different and working to a 12 hour day.
Circadian rhythm, life span, life cycle, photosynthesis, metabolism, migration, sexual patterns. Everything.
I've no idea on the physical science some of those have been touched on above.

 

[sophiecentaur]

completely different

Not "completely". It would be based around all the same chemicals. Photosynthesis would be the main mechanism for energy conversion and for changing the atmosphere from a reducing to an oxidising one. faster diurnal temperature changes so less diurnal variation. That would avoid hottest and coldest extremes in summer and winter.
Smaller or larger leaves on plants? Perhaps not and I cannot think of reasons why.

Loads of material for invention. Perhaps a check with PF when the OP has a scenario in mind?

 

[pinball1970]

Not "completely". It would be based around all the same chemicals. Photosynthesis would be the main mechanism for energy conversion and for changing the atmosphere from a reducing to an oxidising one. faster diurnal temperature changes so less diurnal variation. That would avoid hottest and coldest extremes in summer and winter.
Smaller or larger leaves on plants? Perhaps not and I cannot think of reasons why.

Loads of material for invention. Perhaps a check with PF when the OP has a scenario in mind?

The evolution of the available chemistry would be different so the resulting chemistry would be different. Perhaps different enough not allow self replicating molecules to get started? Or cellular organisms? Or multicellular organisms? Or intelligent life? I would also be interested in arguments on whether liquid water would be around in the quantities it is today.

 

[jim mcnamara]

Early Earth had a daylength of ~4 hours. Over time tidal forces from the moon have slowed the period of rotation. So, for example, during Cretaceous times (Dinosaur times) days were shorter than today, by about 1 hour.

http://www.iea.usp.br/en/news/when-a-day-lasted-only-four-hours
So all this discussion does not seem necessary to me. No massive changes. The Earth already experienced a "spin" factor about 6 times faster than now. Way back at the beginning. So any and all effects of shorter days have already happened. Most of the effects were related to the tidal pull of the moon when it was a whole lot closer to Earth. Land and ocean tides being one of them.

https://en.wikipedia.org/wiki/Earth_tide
And day length is still getting longer - not by a lot, but we can see it expressed for us as 'leap second' -

https://en.wikipedia.org/wiki/Leap_second
In other words, we already did the 'what if' question the OP asked. And more. Case closed, IMO.

 

[pinball1970]

Early Earth had a daylength of ~4 hours. Over time tidal forces from the moon have slowed the period of rotation. So, for example, during Cretaceous times (Dinosaur times) days were shorter than today, by about 1 hour.

http://www.iea.usp.br/en/news/when-a-day-lasted-only-four-hours
So all this discussion does not seem necessary to me. No massive changes. The Earth already experienced a "spin" factor about 6 times faster than now. Way back at the beginning. So any and all effects of shorter days have already happened. Most of the effects were related to the tidal pull of the moon when it was a whole lot closer to Earth. Land and ocean tides being one of them.

https://en.wikipedia.org/wiki/Earth_tide
And day length is still getting longer - not by a lot, but we can see it expressed for us as 'leap second' -

https://en.wikipedia.org/wiki/Leap_second
In other words, we already did the 'what if' question the OP asked. And more. Case closed, IMO.

I disagree, there is no way we can ever reverse the experiment BUT if we changed one of the parameters by a factor of 2 on this Earth thought experiment, do you not think the results would be different? In this case light and heat?

 

[jim mcnamara]

@pinball1970
You do not change Physics of just one thing when you change rotation rate. Radiative heat loss/gain would change. i.e., colder at night, warmer in day --- When you have long periods of rotation compared to shorter periods. Whether you wanted it or not.

You are free to disagree but you're side stepping issues doing so. All of the "fast" rotational effects actually happened really long ago.

To have them persist into the present you need to stop or to slow tidal friction: one way is to lose the moon's effect by having no moon and additional accretion of protoEarth to make up for the loss of that mass.

But. Then you lose other diurnal biological rhythms' effects later. Moon phase affects the timing of teleost (bony fish) egg laying, for example. Those behaviors would never evolve to start with. Not mention the way biological effects work based on the sun's position or longday/shortday - short day plant flowering and reproduction.

The problem with the OP's question is that the examples and some answers given come from all over the place with effects and requirments not accounted for. It's a kind of speculation without physical limits, IMO.

Have fun making up stuff, just try to think it through first. There is a difference between thought experiment and pure unbounded speculation.

 

[jim mcnamara]

My bad. I did not read the purpose of the question: Write a story. Don't worry about Science, this is being moved to world building. Should have done that before now. Sorry.

 

[pinball1970]

My bad. I did not read the purpose of the question: Write a story. Don't worry about Science, this is being moved to world building. Should have done that before now. Sorry.

Yep me too, I thought this was a serious question or thought experiment.

 

[sophiecentaur]

You do not change Physics of just one thing when you change rotation rate. Radiative heat loss/gain would change. i.e., colder at night, warmer in day --- When you have long periods of rotation compared to shorter periods. Whether you wanted it or not.

Why would the mean value of received / radiated heat be different. Based on exponential changes, wouldn't the mean be the same but the peak to peak variation would be less. Is there something else you are including in your idea?

 

[sophiecentaur]

Yep me too, I thought this was a serious question or thought experiment.

I think it turned into one, though. There are a lot of valid ideas to kick around here - perhaps too many for one thread.

 

[pinball1970]

My bad. I did not read the purpose of the question: Write a story. Don't worry about Science, this is being moved to world building. Should have done that before now. Sorry.

Ok @sophiecentaur has suggested this has legs so…

I do not think this is the same sort of wild speculation like the threads asking if life is ubiquitous in the galaxy/universe.

The OP is suggesting a profound change.

You agree our organs including our brain have evolved working to a (roughly) 12 hour period of light followed by a (roughly) 12 period of darkness?

So that is our systems (sleep, sexual behaviour, eating/digestion/excretion, life cycle) our organs that control those systems, our hormones and chemical signalling proteins that control those organs, our cells that produce those functional proteins and therefore our DNA.

That is just the short day without the quicker changes in temperature in 12 periods considered.

Would a mayfly still have evolved to a 12 or 24 hour life cycle? Would a mayfly have evolved to something completely different?

If a mayfly’s life cycle is tuned on its head why not the all the rest?

 

[pinball1970]

I think it turned into one, though. There are a lot of valid ideas to kick around here - perhaps too many for one thread.

I am disagreeing with Jim on biological matters which is probably not a wise thing to do but on this point, I think halving days will impact hugely on biological systems. I do not think it would be just a matter of biology will cope and operate in half the time or do half as much. Ill pick one thing, eating a meal. Our gut operates quite well on 3 meals time for digestion and excretions, enzymes time to make chyme and chyle absorption of nutrients etc etc all work to a roughly 12 hour period. 7am breakfast1 lunch7 tea (Dinner) Nice little 5 hour periods which just happens to be the amount of time the stomach is empty so you feel hungry again Half the day and you get up at 6 eat at 7 then 2 hours after lunch you are ready for bed! Argument would be we would not eat like that shorter period lighter meals more often? Either the way the gut length structure peristalsis enzymes cell morphology would have to be different Perhaps a 6 hour day would not lead to intelligence? Not enough time to eat and increase our brains!

 

[jim mcnamara]

@sophiecentaur - Yes, average temps are the same. No, daily high low temps are not the same.
I am going to map your comment to a real world environment.

Please see the fuzzy plant picture of Tillandsia tectorum-
https://mountaincrestgardens.com/air-plant-tillandsia-tectorum-ecuador-medium-4/
Cute huh? They can survive in a high humidity house for long periods without water. Hence the name "air plant". The best part is you cannot tell when you've killed them by not spritzing them often enough. Perfect for my house.

These Andean plants are epiphytes and occur in the Puna (Altiplano) region above ~3500m. They are fully dependent on 24 hour days with fairly equal day/night durations -12 hours - throughout the year:
The lowest daily temperature is generally below frost and occurs at about 5:00 am local time.
The highest temperature is at about 3:00pm and is about 25° C.
So we can take 12°C as the average.
Almost no precipitation.

Virtually all of the plant species high up there are fuzzy (not a botanical term) because that is how they get moisture. Fog does not go up that high, although there can be a few minutes when a foggy haze forms as the frost melts and evaporates.

Frost forms pre-dawn. When the sun first hits the fuzz, it melts and drips off the fuzz onto the ground or accumulates on special spongy tissues on those weird leaves. This is these plants sole form of water input. This view is simplified a bit. There are other species of gigantic plants up there that really drip a lot.

My contention is: a 6 hour day would have an average 12°C as well. But it would not get cold enough at night to freeze water. 6 hours is not long enough for radiative cooling to do that. The fuzzy things would not have evolved. Maybe: The plants would have evolved drip tips instead. But even lower temperatures squeeze more water out of the air. Who knows, it may have just been lichen covered rocks that survive.

This is just a very localized example. Kind of like your motivation: heating a dwelling.

I do not know how shorter radiative day/night duration would affect meteorology. Diurnal period and relative temperature max/min changes definitely affect extant living things.

 

[sophiecentaur]

My contention is: a 6 hour day would have an average 12°C as well. But it would not get cold enough at night to freeze water.

That's a point I hadn't thought of and it probably would mean that there would be more contrast in the amount of ice present from equator to poles. Lack of ice in our temperature regions would be balanced by more permanent ice in semi arctic regions (there would have to be a symmetry in this).

I have read and seen TV progs about the phenomenon of Evolutionary Convergence, which is based on observations that any isolated region tends to throw up a population of flora and fauna with bands of species which have very obvious functional parallels with the rest of the world. So you find your prey species, your predator hierarchy, your various composters etc and the same with the flora. So, bearing in mind the same original mix of available chemicals, there is likely to be a similar mix of life with (of course) some differences in size and habit but a very similar basic form.
I can't think why mammals, or equivalent, would not develop and they could be smarter or dumber than our present ones.
I could imagine a difference in overall size of animals because that is already seen in regions of extreme climate. More (or fewer) polar bears perhaps. An equivalent to the Wooly Mammoth might be bigger or smaller.

7am breakfast

1 lunch

7 tea (Dinner)

Lol. A very cosy scenario. What about cows in a field that eat all day and lions that eat like lords after a kill and then sleep for a couple of days?

 

[pinball1970]

That's a point I hadn't thought of and it probably would mean that there would be more contrast in the amount of ice present from equator to poles. Lack of ice in our temperature regions would be balanced by more permanent ice in semi arctic regions (there would have to be a symmetry in this).

I have read and seen TV progs about the phenomenon of Evolutionary Convergence, which is based on observations that any isolated region tends to throw up a population of flora and fauna with bands of species which have very obvious functional parallels with the rest of the world. So you find your prey species, your predator hierarchy, your various composters etc and the same with the flora. So, bearing in mind the same original mix of available chemicals, there is likely to be a similar mix of life with (of course) some differences in size and habit but a very similar basic form.
I can't think why mammals, or equivalent, would not develop and they could be smarter or dumber than our present ones.
I could imagine a difference in overall size of animals because that is already seen in regions of extreme climate. More (or fewer) polar bears perhaps. An equivalent to the Wooly Mammoth might be bigger or smaller.Lol. A very cosy scenario. What about cows in a field that eat all day and lions that eat like lords after a kill and then sleep for a couple of days?

Yes I meant humans on the three squares a day! (Ha ha!)
Cows are a good example, the cow would NOT be able to chew all day because the day would be half as long.
Lions could not sleep all day because they would not have the time to do it.
Sleeping on a huge meal is not great for digestion, perhaps not as bad for lions but not great for us.
Smaller stomachs, smaller everything else I think.

 

[sophiecentaur]

There are plenty of plants and animals that have a near 12 hour cycle. The tides have at least as big an influence on coastal organisms. Seals and the like (I.e. Mammals even) are not bothered by the light when they hunt for mollusks at high tide.
Lions don’t care if it’s day or night if they want to sleep for 24 hrs.
Perhaps our descendants will answer this question if ever there is ‘colonisation’ of distant systems but din’t hold yer breath.

 

[sophiecentaur]

Chewing for two half days is a good as chewing one whole day, btw.

 

[pinball1970]

Chewing for two half days is a good as chewing one whole day, btw.

Stood out in the field in the dark?

 

[hutchphd]

Why would the mean value of received / radiated heat be different. Based on exponential changes, wouldn't the mean be the same but the peak to peak variation would be less. Is there something else you are including in your idea?

I think the equilibrium temperature shifts.
Have you ever done the simple black body radiation balance equations for the Earth and sun ?

You can show, using only T_sun =6000K and that 215xsolar radius=1 astronomical unit, that simple black body radiative balance puts the average Temperature of the Earth at just under 300K assuming the Earth radiates uniformly. I find this a wonderful result!

If the Earth rotates more slowly, the local extrema of surface Temperature will be more pronounced.

The T⁴ means that radiation will be enhanced by this local variation in T and so the Earth will, on average, radiate more and therefore be cooler if it rotates more slowly. Note that the average influx from the sun is unchanged.

So I believe with faster rotation T asymptotically approaches the "uniform" resulting T from below.

 

[sophiecentaur]

I was assuming that the system would be like an RC charge/discharge situation but the T⁴ business changes that.

 

[essenmein]

Re the oceans, I do believe that the water would rise more in the equator, from what I remember reading is the Earth is about 20km "fatter" in the middle (around the equator), that's rocks etc. And the ocean I think I read is about 10km higher on top of that in the equator due to the very subtle diff in effective gravity (centrifugal accel is opposite in direction to gravity), eg you are ~0.5% lighter at the equator vs the poles.

Note that height data is actually taken from the case of "what if the Earth stops spinning", where the oceans would rush to the poles and the equator would be a single mega continent.

Now consider that centrifugal acceleration increases with square of angular velocity, doubling rotational speed will have quite the impact on sea levels!

Now off course if the Earth developed this way, with the extra rotational speed, who knows what that would look like, but if over the course of a small ish amount of time (say a few years or a decade) you sped the Earth up, then I do believe the equator would be under water.

 

[DrStupid]

Now consider that centrifugal acceleration increases with square of angular velocity, doubling rotational speed will have quite the impact on sea levels!

It would have an inpact on the shape of Earth but I'm not sure about the sea level. How long would it take to reach the hydrostatic equilibrium?

 

[essenmein]

It would have an inpact on the shape of Earth but I'm not sure about the sea level. How long would it take to reach the hydrostatic equilibrium?

Do you think the rocks and dirt would respond more quickly to changes in net acceleration than water?

I would say depending on how quickly this rotation speed changed (ie the act of accelerating the angular velocity of the planet on its own would cause havoc if it happened too fast), the effect on the water would be quite quick, I would imagine in the order of hours or days. Consider that a bulge of water is dragged around by the moons gravity constantly, ie the tides.

 

[hutchphd]

If the rotation changed suddenly the ocean would "slosh around" for a while. If you know the damping you could estimate how long...I bet you can find the damping factor by examining the phase of the tidal response relative to the driving gravity gradient. This would be a bit complicated by the two driving gravities (sun and moon). Anyone know of such an analysis?

 

[DrStupid]

Do you think the rocks and dirt would respond more quickly to changes in net acceleration than water?

Why need the rocks to be faster? It is sufficient if they respond as fast as water.

Consider that a bulge of water is dragged around by the moons gravity constantly, ie the tides.

The Earth tides have the same period.

 

[essenmein]

Why need the rocks to be faster? It is sufficient if they respond as fast as water.
The Earth tides have the same period.

Point is water flows very readily, rocks do not, in other words the reason we see water flowing about with the moon, and don't get earthquakes instead, is because water moves far more readily than rock. Tidal forces do act on rocks as well (obviously), but thankfully those forces are not large enough on this planet for us to notice.

In other words off course water will respond to a change in Earth rotation, geologically speaking it will do this essentially instantly (with some sloshing about as it settles), rock will also move, but that will take a lot more time.

 

[DrStupid]

Point is water flows very readily, rocks do not

They don't need to flow. A vertical displacement is sufficient.

Tidal forces do act on rocks as well (obviously), but thankfully those forces are not large enough on this planet for us to notice.

That's not a matter of force. We don't notice because we are moving together with the rock up and down every 12 hours. The rock follows pretty much the full deformation of the geoid caused by the tidal forces of Earth and Moon.

In other words off course water will respond to a change in Earth rotation, geologically speaking it will do this essentially instantly (with some sloshing about as it settles), rock will also move, but that will take a lot more time.

I don't see any justification for this claim. If the rock can't even resist a deformation in meter-range twice daily how should it keep a 21 km deformation for "a lot more time"?

 

[essenmein]

They don't need to flow. A vertical displacement is sufficient.

Increase in height means more volume, which means more water, and that water had to come from somewhere.

 

[mfb]

Tidal forces do act on rocks as well (obviously), but thankfully those forces are not large enough on this planet for us to notice.

The LHC needs to take them into account.

Increase in height means more volume, which means more water, and that water had to come from somewhere.

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.

 

[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.