What if the Earth stopped spinning?

Ever asked yourself a crazy hypothetical question?

Like, “What would happen if the Earth instantly stopped spinning, but the atmosphere kept travelling at the same speed?”

What do you think would happen? Choose something specific in the world (e.g. people, the ocean, buildings, sand, trees, cars) and jot some quick notes about what you think would happen (and how one thing causes another).

Randall Munroe is a web cartoonist and former NASA engineer who answers this question in his book, What If?

Here’s the shortest version of his answer:

Nearly everyone would die. Then things would get interesting.

What If?(2014)

Is that what you had?

Why do you think that’s his answer? What could be his reasoning?

Terrible things happen

From What If?

Take another guess. Why would everyone die? (And what would make things “interesting” afterwards?)

How did you go? Did you have any ideas?

Randall Munroe spends several pages walking through this scenario, but here’s how he describes the first couple of steps:

At the equator, the Earth’s surface is moving at about 470 meters per second — a little over a thousand miles per hour — relative to its axis. If the Earth stopped and the air didn’t, the result would be a sudden thousand-mile-per-hour wind.

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 percent of the world’s population — would suddenly experience supersonic winds.

The highest winds would last for only a few minutes near the surface; friction with the ground would slow them down. However, those few minutes would be long enough to reduce virtually all human structures to ruins.

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

What If?(2014)

Munroe argues that if the Earth stops rotating, then winds become so fast that they smash all the buildings, which kills everyone inside them and creates debris that kills everyone outside them.

That's cause & effect reasoning!

Sometimes your reasoning needs to be quite detailed in order to be convincing or accurate.

For example:

Why would everyone die?
Because the world would experience supersonic winds.
But why would the winds be that fast?

To answer that question, you could explain the chain of cause & effect in more detail:

The winds are already that fast! The trick is that, because of the rotation of the Earth, buildings on the ground travel almost as fast as the wind.
But if the Earth stopped spinning, then the wind would suddenly be travelling at its full speed relative to the ground, with enough force to obliterate any building on the surface, killing everyone inside, and pulverising with debris any people standing downwind.

By adding explanatory detail, we can unpack all the little links in the chain—as well as explain why other links might not be true.

frankenstories_naive_illustration_of_a_city_scene_with_buildings blown down

This example is what we call a chain of cause & effect because one event triggers another, which triggers another, and so on, in a line.

It’s also what we call a prediction because we follow the chain of cause & effect into the future.

Next, let’s look at an example where the causes are in a clump instead of a chain and where we are explaining the past instead of the future.

Bunkers blown

From What If?

Two types of reasoning

What if the Earth stopped spinning?