You can use this stupid game to do some serious physics

9 months ago

I’m a sucker for interesting online games in which there is neither a score nor even a goal. In this case, it’s an animated space sim to promote the book. What if? 2 Randall Munro, author hkkd comics.

you can play it clicking here. (Don’t worry, I’ll wait.)

The game works like this: you start with a rocket on a very small planet. Click on the rocket to start, then you can use the arrows on your keyboard to turn on the engine, turn the spaceship around and find other planets and a few fun things that are mostly inside. What if jokes. That’s all. It’s a game. It’s silly and fun and I love it.

But it turns out that you can even use a simple game to learn some of the key concepts in physics.

Real orbits

One of the features you can see on the original planet is a recreation of a Newtonian cannonball, or Isaac Newton’s thought experiment on the relationship between a fast-moving projectile and orbital motion. Newton said that if you could shoot a very fast cannonball horizontally from a very high mountain, perhaps the curve of its trajectory would match the curvature of the Earth. This will cause the cannonball to fall but never hit the ground. (This is essentially what happens to an orbiting object like the International Space Station, only the ISS was not filmed from a high mountain.)

After seeing Newton’s cannonball, I assumed that I could send my spacecraft into orbit around this tiny planet, which would be fun. I tried it right away using the arrow keys but without much success. Every time I almost put it into a stable orbit, it didn’t last long. This got me thinking about whether the physical interactions that govern the orbits in What if the world is no different from those in the real universe.

The first physical concept applicable to orbital motion is, of course, gravity. Between any two objects that have mass, there is a gravitational interaction. For example, there is an attractive force between the Earth and the pencil you hold in your hand because they both have mass. If you let go of the pencil, it will fall.

If you are standing on the surface of the Earth, the gravitational force acting on the pencil appears to be constant. However, if you bring this pencil far enough from the Earth (for example, within 400 kilometers of the ISS), you will notice a decrease in gravitational interaction: the pencil will weigh less, and it will take longer for it to get to the Earth. Autumn.

We can model the gravitational force between two objects with the following equation:

Illustration: Rhett Allen

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