What if the Earth Suddenly Stopped Spinning?

I've been asked this one a few times, in slightly different ways by slightly different people, including Will's "If the earth reversed on its axis, what would be the consequences?" and Shailendra's "If Earth stops rotating what would be its effect on gravitation at the equator?" so I'll try to look at it from various angles over the next few posts (you can pick those up at the spin me right round tag)...

What if the Earth suddenly stopped spinning?

If some great and bountiful ruler of all* suddenly slammed on Earth's brakes it'd be pretty bad news for us all.

Anyone standing at the Earth's equator is, without putting any effort in at all, moving at over a thousand miles per hour** because that's how fast the Earth beneath their feet is rotating. As you move closer to the poles your speed is slower because you're closer to the axis of rotation***. When you're standing still in London, you're actually moving at about 650 miles per hour, relative to the centre of the Earth.

So imagine that you're standing at the equator as the Earth suddenly stop spinning. What do you notice? The truthful answer is that you probably won't notice anything as you've suddenly started flying east at a thousand miles per hour.

Actually, it's not the case that you've started flying east. What's actually happening is that as the Earth is spinning you have momentum and, for whatever reason the Earth stops, when it stops you still have that momentum. The ground beneath your feet stops moving at a thousand miles per hour, but you don't. So you suddenly fly sideways at 1000 miles per hour, but the Earth is a sphere and you're travelling in a straight line which means that, as far as you're concerned, you're flying upwards as you go sideways, rather than staying the same distance from the surface of the Earth. You'll start off at 1000 miles per hour but because of air resistance you'll slow down as you go, until eventually Earth's gravity takes over and you plummet back to Earth.

If you're actually standing in London it doesn't seem so bad at first: you'll be hurled eastwards at a mere 650 mph, which is relatively sedate until you find yourself hitting St Paul's Cathedral at just under 650 miles per hour. That is if St Paul's Cathedral is still standing, of course, which it probably won't be as it, too, will be suffering from suddenly feeling the effects of its gathered momentum. As will cats. And zebras. And everything else on the Earth's surface. Except Santa's house at the North pole: that'll feel a twisting force, and spin a little bit. But not much.

It won't just be things on the Earth's surface that will feel the effects either: Earth's surface itself has a lot of momentum that it'll need to get rid of. This will cause all sorts of stresses and strains, and we all know what stresses and strains in the Earth's crust means: earthquakes.

The seas will be flung eastwards at their respective latitudes as well, so expect tsunamis on west coasts planet-wide.

So, in short, you don't really want to know what will happen if the Earth suddenly stops spinning, but your best bet is to make sure you're at the poles.

* For the record, I don't believe there is one, but I'm invoking one for the purposes of avoiding my inner pedant having to chat about things that could cause the Earth to stop spinning, and whether it was actually possible.
** This is, of course, all relative.
*** Think about a couple of ants on a car tyre if you don't understand this one: an ant hanging on for dear life out towards the rim is moving a lot faster than an ant sitting half way out from the centre because it's travelling further than the second ant, but in the same amount of time. An ant sitting in the centre of the wheel isn't moving at all (relative to the wheel itself). He's just really, really dizzy.


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