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[lemon10]

The earth is spinning pretty fast, but not nearly as fast as you would need it to be for an object its size to have a significant impact on weight. There is an effect, but its quite small. That said, there would be a measurable increase in effective weight for a few days, but it wouldn't really significant.

This question is about if the earth magically reversed direction over a week, not about trying to reverse it.

Yes, I know that. How magically though? Just the solid bits? Or is it magical enough to rotate the atmosphere? Because then you're just reversing all the weather patterns, all of the ocean currents, and the climate would 'just' be mirrored as closely as physical constraints allow. The more constraints you place on the question, the more interesting it becomes.

Its not 100% clear how magically. But the effect on the weather patterns would happen either way as there would be a change in the day/night cycle. Similarly, ocean currents would be disrupted by the fact that the sun wouldn't be shining on them for a few days, and would presumably change after the sun rises in the west instead of the east.

[RedKing]

If movies have taught us anything (they haven't), it's that time would go backwards.

The climatological effects are interesting to guess at. Mongolia would become significantly wetter, Eastern Europe would become a desert, the tropical monsoon cycles would likely be reversed (having huge impacts on agriculture and native flora/fauna), and the eastern side of the Appalachians would become an orographic rain shadow, and California would become even more of a desert.

I'm also not sure what reversing the rotation does to the orbit.

EDIT: Also, much smarter people than us have already pondered this.

[Eagleon]

EDIT: Also, much smarter people than us have already pondered this.

Oh, well, sorry then. I'll stop pondering at once.

[Il Palazzo]

I'm also not sure what reversing the rotation does to the orbit.

It only affects tidal interactions, which in the time scale of the life of the solar system have significant impact only on Moon's orbit.

What about gravity? Since Earth is spinning this fast, there must be a significant force pushing us outwards, and it'd disappear as the rotation speed reaches zero.

As someone calculated earlier, the rotational velocity of the Earth on the surface is negligible.

It's not, though. It might not be much for a test particle, but it adds up over the volume of the planet.
It's what makes the Earth an oblate spheroid - ~20 km flatter at the poles than at the equator. If you stop the rotation, the surface would have to follow the changing equipotential surface, relaxing to a spherical shape and back to the spheroidal one as it starts spinning in the other direction.
20 km might not seem like much w/r to the radius, but even Earth tides caused by the moon (which reach 50cm tops) are known to affect volcanism.
Unless the magic of rotation change keeps the surface magically rigid throughout the process, there would be quakes and eruptions.

[Culise]

EDIT: Also, much smarter people than us have already pondered this.

That said, I think that article overstates the effect of rotation on the Earth's internal dynamo.  It's as much driven by thermal forces creating a cyclic rise and fall in the molten outer core, and those thermal gradients come from pressure forces rather than rotational velocity.  Indeed, the main axis of the magnetic field is off by a significant amount from the rotational axis of the Earth, which is why the magnetic poles are in Canada and off the coast of Antarctica.  I mostly point it out because I almost made the exact same mistake.  Coriolis forces do play a significant role, but over the course of three days, I don't think there'll be severe effects before the magnetic field returns to full strength.

That, of course, does also rely on how much magic is being used to reverse the Earth's rotation, though. 

[FearfulJesuit]

An unusually knowledgeable amateur has actually made a pretty good guess at this one. Instead of reversing the Earth's rotation, he's simply turned it upside-down in the same direction, but from a climatological perspective, that should be basically the same thing.



The reversal in currents would create new ice caps in Scandinavia and Siberia, lowering the sea level. He speculates that the cradles of civilization will be the Mississippi valley and China, both of which will be arid flood plains. Europe will probably be a backwards footnote to most of history, while formerly dry areas (the Sahara, Australia) will be heavily-populated breadbaskets.

Interesting idea for an alternate timeline.

[Zanzetkuken The Great]

Here's another possibility to explore:  How would the climate and our civilization be affected if the world's rotational pole was aligned with its magnetic pole, and shifted along with the magnetic pole?

[Loud Whispers]

Spoiler (click to show/hide)

An unusually knowledgeable amateur has actually made a pretty good guess at this one. Instead of reversing the Earth's rotation, he's simply turned it upside-down in the same direction, but from a climatological perspective, that should be basically the same thing.



The reversal in currents would create new ice caps in Scandinavia and Siberia, lowering the sea level. He speculates that the cradles of civilization will be the Mississippi valley and China, both of which will be arid flood plains. Europe will probably be a backwards footnote to most of history, while formerly dry areas (the Sahara, Australia) will be heavily-populated breadbaskets.

Interesting idea for an alternate timeline.

Important question; WHAT OF MONGOLIA?