If the earth started spinning clockwise

[Flustered]

If the Earth started spinning clock wise but still in the same orbit it is in now. What would some effects be? Also if the Earth started orbiting in the opposite direction would there be any side effects? And does the Earth even spin counter clockwise? I suppose looking down from the north pole it does but if you look at it from the south pole it would be clockwise?

 

[SHISHKABOB]

the sun would rise in the west and set in the east

all Coriolis effects would be reversed

nothing too interesting

 

[Drakkith]

I want to say that the Moon would begin to lose orbital angular momentum due to tidal effects and it's distance from Earth would slowly diminish over a few billion years. And yes, looking at the Earth from the south pole it would be spinning clockwise.

 

[Flustered]

If the Earth spun different, why would that effect the moon? The gravity from Earth would still be the same. Also that means that every single planet spins counter clockwise and clockwise correct?

 

[Drakkith]

If the Earth spun different, why would that effect the moon? The gravity from Earth would still be the same. Also that means that every single planet spins counter clockwise and clockwise correct?

The rotation of the Earth causes the tidal bulges to move ahead of the moon and to pull it forwards just a little bit. This results in a gradual climb away from the earth. If the Earth spun backwards the bulges would pull the moon from the other side, against its orbital motion. This is one reason why most moons orbit in a direction that is with their planets rotation, the opposite direction is very unstable.

 

[Janus]

If the Earth spun different, why would that effect the moon? The gravity from Earth would still be the same. Also that means that every single planet spins counter clockwise and clockwise correct?

It's a tidal force effect. Right now the interaction between Earth and Moon causes a transfer of angular momentum that slows the Earth's rotation while moving the Moon further away.

However, if the Earth rotated in the opposite direction than the Moon orbited this effect would have the opposite effect, causing the Moon to draw closer to the Earth.

On another note, if the Earth rotated in the opposite direction, days would be ~18 minutes shorter, resulting in about 5 more days to a year, requiring a new calendar and new clocks.

 

[haruspex]

On another note, if the Earth rotated in the opposite direction, days would be ~18 minutes shorter, resulting in about 5 more days to a year, requiring a new calendar and new clocks.

I thought it would be exactly 2 more days, each day being about 8 minutes shorter.

 

[Flustered]

Kind of off subject but how did Galileo record Jupiter's moons in consecutive days for about 5 days and each drawing one of the moons orbited to the other side of the planet?

 

[Janus]

I thought it would be exactly 2 more days, each day being about 8 minutes shorter.

Oops. Right.

 

[sophiecentaur]

Kind of off subject but how did Galileo record Jupiter's moons in consecutive days for about 5 days and each drawing one of the moons orbited to the other side of the planet?

Interpolation?

 

[Khashishi]

Whether you call the current rotation clockwise or counterclockwise is arbitrary and depends on whether you are looking down from the North pole or up from the South pole. If you changed the rotation suddenly, there would be massive transient effects, but if you somehow ignored the transient effects, I don't think there'd be too much long term effect. I'm guessing the transient effects (hurricanes like the world has never seen) would kill us all.

 

[sophiecentaur]

Problem with these scenarios is setting up the conditions under which they could actually occur (even just in thought). Most of the large objects in the Solar system rotate in the same sense, because of the way things started off and settled down. The Moon is tidally locked to the Earth and the Earth is heading that way with the Moon too (enormous time scale). If the Earth's rotation were to be reversed then the moon would be dragged closer and closer until it crashed. But any event that could cause the original change would need to be immense and extremely well orchestrated to avoid nudging the Moon in some way. Would you use enormous rockets? In which case the ejecta would probably affect the Moon too. It might be easier to set the Moon off in a reverse orbit and discuss what happens then. (Crash, again)

God knows what the tides would be like near the end.

 

[Bob S]

Angular momentum has to be conserved, it will not change direction. So the only possibility is that the Earth's body orientation changes without changing the angular momentum vector. As long as the Earth is spinning about either its major (maximum moment of inertia) principal axis or its minor (minimum moment of inertia) principal axis, the Earth is stable. But if for some reason, the Earth body principal moments of inertia shifted (e.g., by major earthquake) such that the Earth were spinning about its intermediate principal moment of inertia, then the Earth's north and south poles could flip without affecting the angular momentum vector. In short, "the polhode will continue rolling on the herpolhode in the invariable plane without slipping". A good youtube demonstration of pole flipping was recently carried out on the International Space Station. See

 

[Flustered]

What equation would one use to calculate the time it would take for the Moon to crash into Earth, if the Earth reversed its spin.

 

[Bob S]

What equation would one use to calculate the time it would take for the Moon to crash into Earth, if the Earth reversed its spin.

The effect would be negligible, as long as the angular momentum vector of the Earth is unchanged.

 

[Flustered]

The effect would be negligible, as long as the angular momentum vector of the Earth is unchanged.

Someone earlier said the tides of the ocean would change the Moons orbit.

 

[gmax137]

?... See

Thanks, that is just too cool. Plus guys like Newton could see that in minds eye, without the ISS or YouTube. We are lucky today...

 

[Flustered]

Maybe I'm lost but what is the significance of the rotating book?

 

[Bob S]

Someone earlier said the tides of the ocean would change the Moons orbit.

If the Earth's angular momentum is unchanged, and the Earth's body axis flipped say over in a year (365 revolutions), an observer on Earth would see the east→west direction of the tides change by ~3 degrees per day to west→east. An observer in space would say that the Earth's tides did not change direction, but would say that the north and south poles flipped.

By the way, the vector sum of the Earth's and Moon's angular momentum is conserved. When the Earth's rotation slows due to tidal forces, down, the Moon's angular momentum increases due to tidal forces, and moves to a higher orbit.

Read "...First there is a real retardation of the Moon's angular rate of orbital motion, due to tidal exchange of angular momentum between the Earth and Moon. This increases the Moon's angular momentum around the Earth (and moves the Moon to a higher orbit with a slower period). Secondly there is an apparent increase in the Moon's angular rate of orbital motion (when measured in terms of mean solar time). This arises from the Earth's loss of angular momentum and the consequent increase in length of day.[8]" in http://en.wikipedia.org/wiki/Tidal_acceleration

 

[Bob S]

Maybe I'm lost but what is the significance of the rotating book?

Watch very carefully when the book is rotating about its intermediate principal moment of inertia axis. Note that the book binding is flipping from the left side to the right side, and back.

 

[Flustered]

Watch very carefully when the book is rotating about its intermediate principal moment of inertia axis. Note that the book binding is flipping from the left side to the right side, and back.

Yes I observed that, but what does this prove? Did someone think that was impossible?

 

[Bob S]

Yes I observed that, but what does this prove? Did someone think that was impossible?

Au contraire. Physicists realized not only that it was possible, but had to occur when a solid body spins about its intermediate moment of inertia axis...

 

[Flustered]

So you are saying that the Earth may go through this flip?

 

[D H]

So you are saying that the Earth may go through this flip?

No, it's not. Sans some external torque, angular momentum is a conserved quantity. Your flip ("if the Earth started spinning clockwise") does not conserve angular momentum. It would require a huge, huge, huge, external torque.

Your question is essentially one of those "what do the laws of physics say would happen if we found a way to violate the laws of physics" kind of questions.

 

[Bob S]

No, it's not. Sans some external torque, angular momentum is a conserved quantity. Your flip ("if the Earth started spinning clockwise") does not conserve angular momentum. It would require a huge, huge, huge, external torque.

Are you saying that this demonstration on the International Space Station does not conserve angular momentum?

 

[D H]

Are you saying that this demonstration on the International Space Station does not conserve angular momentum?

First off, the top of the book is always turning toward the camera. There is no reversal of the angular velocity vector here.

Secondly, this is a book, an object with three very distinct principal axes. Labeling the principal moments of inertia as A, B, and C, with A<B<C, for this book the ratio of the largest moment of inertia to the smallest, C/A, is about 3. The intermediate unstable axis B has an moment of inertia that is just about ideally placed in terms of maximizing tumble. Compare that to the Earth. The Earth is very close to a symmetric top; the ratio (B-A)/C is very, very tiny. Moreover, the ratio (C-A)/C is about 1/309. The large scale tumbling seen in that video becomes a tiny little thing called the Chandler wobble with the Earth.

Thirdly, this is a book, a rigid body. The Earth is an elasto-plastic body. This makes the behavior deviate from that of a rigid body. The Chandler wobble doesn't have quite the frequency one would expect for a rigid symmetric top. The magnitude of the wobble oscillates, alternately damped and excited by the polar tide.

There is a phenomenon called polar wander, but this does not involve the Earth spinning in the opposite direction. Apparent polar wander results from the motion of the tectonic plates. True polar wander results when the mantle changes orientation. The Earth's rotation axis when viewed from an inertial frame doesn't wander. It is the continents, and possibly the mantle, that wander. This is a very slow process, a degree or so per million years. Whether true polar wander ever did occur remains a bit contentious. There are several articles in the scientific literature arguing for various true polar wander events. There are also articles arguing against such events.

 

[Bob S]

First off, the top of the book is always turning toward the camera. There is no reversal of the angular velocity vector here.

Secondly, this is a book, an object with three very distinct principal axes. Labeling the principal moments of inertia as A, B, and C, with A<B<C, for this book the ratio of the largest moment of inertia to the smallest, C/A, is about 3. The intermediate unstable axis B has an moment of inertia that is just about ideally placed in terms of maximizing tumble. Compare that to the Earth. The Earth is very close to a symmetric top; the ratio (B-A)/C is very, very tiny. Moreover, the ratio (C-A)/C is about 1/309. The large scale tumbling seen in that video becomes a tiny little thing called the Chandler wobble with the Earth.

Thirdly, this is a book, a rigid body. The Earth is an elasto-plastic body. This makes the behavior deviate from that of a rigid body. The Chandler wobble doesn't have quite the frequency one would expect for a rigid symmetric top. The magnitude of the wobble oscillates, alternately damped and excited by the polar tide.

There is a phenomenon called polar wander, but this does not involve the Earth spinning in the opposite direction. Apparent polar wander results from the motion of the tectonic plates. True polar wander results when the mantle changes orientation. The Earth's rotation axis when viewed from an inertial frame doesn't wander. It is the continents, and possibly the mantle, that wander. This is a very slow process, a degree or so per million years. Whether true polar wander ever did occur remains a bit contentious. There are several articles in the scientific literature arguing for various true polar wander events. There are also articles arguing against such events.

A necessary (but not sufficient) prerequisite for an Earth pole reversal without changing the angular momentum vector is reducing the moment of inertia about the C (polar) axis by about 3 x 10³⁵ kg-m². This is equivalent to moving about 7.5 x 10¹⁸ metric tons (7.5 x 10⁹ cubic km) of water from the equator to the poles as an ice cap. Considering that 2 polar caps, each with a thickness of 1 km and a radius of 1000 km is only 6.3 x 10⁶ cubic km, such a scenario is extremely unlikely.

 

[mfb]

What equation would one use to calculate the time it would take for the Moon to crash into Earth, if the Earth reversed its spin.

Probably a differential equation, where the coefficients come from observation of the tides or maybe a simulation of the sea system on earth.

By the way, the vector sum of the Earth's and Moon's angular momentum is conserved. When the Earth's rotation slows due to tidal forces, down, the Moon's angular momentum increases due to tidal forces, and moves to a higher orbit.

If Earth would spin the other way round (ignore the origin of that for a moment), both would slow down at the same time (in case of the moon, it comes closer to Earth and gets a higher velocity, but lower angular momentum).

There are some moons in the solar system which orbit in the "wrong" direction. But they are usually small, in irregular orbits and probably captured asteroids.

 

[D H]

A necessary (but not sufficient) prerequisite for an Earth pole reversal without changing the angular momentum vector is reducing the moment of inertia about the C (polar) axis by about 3 x 10³⁵ kg-m². This is equivalent to moving about 7.5 x 10¹⁸ metric tons (7.5 x 10⁹ cubic km) of water from the equator to the poles as an ice cap. Considering that 2 polar caps, each with a thickness of 1 km and a radius of 1000 km is only 6.3 x 10⁶ cubic km, such a scenario is extremely unlikely.

That's a bit high. You rounded up, you forgot that increasing the C (polar) moment of inertia necessarily decreases at least one of the other two moments, and you used ice rather than rock. There are signs that the Earth has undergone significant true polar wander.

As a starter,

Joseph L. Kirschvink, Robert L. Ripperdan and David A. Evans, Evidence for a Large-Scale Reorganization of Early Cambrian Continental Masses by Inertial Interchange True Polar Wander, Science 277:5325 pp 541-545 (1997), doi: 10.1126/science.277.5325.541
http://web.gps.caltech.edu/~jkirschvink/pdfs/iitpw.pdf

 

[Bob S]

That's a bit high. You rounded up, you forgot that increasing the C (polar) moment of inertia necessarily decreases at least one of the other two moments, and you used ice rather than rock. There are signs that the Earth has undergone significant true polar wander.

As a starter,

Joseph L. Kirschvink, Robert L. Ripperdan and David A. Evans, Evidence for a Large-Scale Reorganization of Early Cambrian Continental Masses by Inertial Interchange True Polar Wander, Science 277:5325 pp 541-545 (1997), doi: 10.1126/science.277.5325.541
http://web.gps.caltech.edu/~jkirschvink/pdfs/iitpw.pdf

Thank you. From your reference:

A variant of this mechanism, inertial interchange true polar wander (IITPW), involves discrete bursts of TPW of up to 90° in geologically short intervals of time if the magnitudes of the intermediate (I_int) and maximum (I_max) moments of inertia cross (36). This would result in a rapid movement away from the spin axis by the geographic location of the former pole with rotation of the entire solid Earth centered about the minimum moment of inertia (I_min) located on the equator. Because I_max, I_int, and I_min are orthogonal, the simple interchange case (with no independent plate motions) yields a 90° shift. Although such an event has not yet been recognized in the geologic record, the geodynamic consequences of an inertial interchange event have been considered in qualitative terms(36). These analyses predict that the 90° rotation of an IITPW event should happen over an interval of 10 to 15 My.

So maybe an interhange of moments of inertia did cause the Earth to spin about an axis that was somewhere near the present equator.