Well, first nearly everyone would die.

Then things would get interesting.

At the equator, the Earth's surface is moving at about 470 meters per second, a little over a thousand miles an hour, relative to its axis.

If the Earth stops and the air doesn't, the air there will suddenly be moving over the surface at 470 meters per second.

For reference, supersonic speed is 343 meters per second.

The wind would be highest at the equator, but everyone and everything living between 42 degrees north and 42 degrees south, which includes about 85% of the world's population, would also experience sudden supersonic winds.

The high winds would only last for a few minutes near the surface before friction with the ground slowed them down.

However, those few minutes would be long enough to reduce virtually all human structures to ruins.

Even structures strong enough to survive the winds themselves would be in trouble.

As comedian Ron White said about hurricanes, "It's not that the wind is blowing, it's what the wind is blowing."

Say you're in a massive bunker made out of some material which can withstand thousand-mile-per-hour winds.

That's good, and you'd be fine if you were the only one with a bunker.

Unfortunately, you probably have neighbors, and if the neighbor upwind of you has a less well-anchored bunker, your bunker will have to withstand a supersonic impact by their bunker.

My home in Boston is far enough north to be just barely outside the supersonic wind zone, but the winds here would still be twice as strong as those in the most powerful real-world tornadoes.

Buildings would still be smashed flat, torn from their foundations, and sent tumbling across the landscape.

Winds would be lower near the poles, but no human cities are far enough from the equator to escape devastation.

The highest-latitude city on the planet is on the island of Svalbard in Norway, and even it would experience winds equal to those in the planet's current strongest tropical cyclones.

Even so, the human race wouldn't go extinct.

True, very few people above the surface would survive.

The flying debris would pulverize almost everything.

However, a lot of people below the surface of the ground would survive the initial event just fine.

There would be other lucky survivors, like the scientists and staff at the Emmons and Scott Research Station at the South Pole.

The surface of the Earth at the South Pole isn't moving relative to the Earth's axis because it's on the axis.

People there would simply lose contact with the outside world.

They'd probably be confused, until someone noticed that the sun had stopped moving across the sky.

Then they'd be really confused.

Back at the equator, things would get really weird.

Winds sweeping over the oceans would have been churning up and atomizing the surface layer of the water.

For a while, the ocean would cease to have a surface at all.

It would be impossible to tell where the spray ended and the sea began.

As the energy of the blasting wind began to dissipate, it would mostly go into heat.

A lot of heat.

But oceans are cold.

Below the thin surface layer, there are fairly uniform 4 degrees Celsius.

The wind-blown spray would be heated by contact with the hot air and carried up into the layers of air still blowing above, making room for more cold spray, which would be heated and rise, and so on.

The subsequent turbulent mixing would likely trigger worldwide thunderstorms over the oceans.

The wind would also have momentum, which would transfer into waves, which would sweep around the globe, west to east, and every west-facing shore would encounter the largest storm surge in world history.

It would be like a combination of normal wind-driven waves and a tsunami.

A turbulent wall of water would flow ashore, reaching in some places many miles inland.

Eventually, a dense blanket of fog would settle over the cold ocean surfaces.

Normally, this would cause global temperatures to plummet.

And they would, at least on one side of the Earth.

If the Earth stopped spinning completely, the normal cycles of day and night would end.

The Sun wouldn't completely stop moving across the sky, but it would slow down a lot.

As the Earth's orbit carried us in a circle, we would see the Sun rise and set exactly once a year.

Well, not exactly once a year.

The momentum of the atmospheric winds would get transferred back to the Earth, starting it spinning again very slowly, since the atmosphere is much lighter than the Earth.

Relative to the distant stars, a single spin of the Earth would now take around 3,000 years to complete.

So for all practical purposes, the once-per-orbit day, that lasts a year, would win out.

Earth would experience six months of daylight and six months of night.

On the day side, the surface would bake under the constant sunlight, while on the night side, the temperature would plummet.

Although the length of the day would change, the length of the month would not.

The Moon hasn't stopped revolving around the Earth.

In fact, the Moon, our faithful companion, would act to partly undo what Andrew has done.

Remember, this is all Andrew's fault.

Before Andrew, the Earth's tidal bulge, created by the Moon's gravity, slowed down our rotation while dragging the Moon into a higher orbit.

After Andrew stopped the Earth's rotation, the Moon's gravity would tug on the Earth and very, very, very gradually speed us up again just a little while it slowed down.

Until eventually, someone could again ask, what if the Earth suddenly stopped rotating?

Thank you, Moon.