Because Randall Munroe isn't doing "What If" as much these days...

How fast would the Earth need to spin in order for the centrifugal force to throw us off of it (or those of us near the equator at least)?

What else would happen if the earth spun that fast?

No need to do the math -- the answer is the same as the question "What's the period of a low equatorial orbit?", because both are about how long it takes to circle the Earth at about ground level without experiencing any net gravity. About 90 minutes for equilibrium: any faster than that, and the orbital launch velocity at the equator goes negative.

As for what would happen, it would probably be bad even by "What If" standards. Atmosphere and oceans would both bunch up at the equator as the Earth spun up, before being flung off into a ring-like structure. But that's treating the bedrock as rigid, which it very much isn't. Eventually the continental plates would buckle and split, and molten or fractured rock would start to join the ring. That of course would reduce the gravitational pull of Earth sensu strictu, so eventually a new equilibrium would be found.

Peter

Yeah, that sounds about right for a "What If" scenario. I think my favorite (and also the most disgusting) is still the "mole of moles." That one ends pretty badly. Well, they almost all end really, really badly.

Ah! Good point. That's about 17,000 miles per hour. Yeah, our atmosphere would peel away quite quickly wouldn't it? Then everything else.