I’m a loser for interesting online games that haven’t got a rating or perhaps a goal. In this case, it’s a comic book book space simulator to advertise the book What if? 2by Randall Munroe, writer of xkcd comics.
You can play it by clicking here. (Don’t worry, I’ll wait.)
The game works like this: you begin with a rocket on a really small planet. Click on the rocket to start out then use the keyboard arrows to activate the engine, turn the spaceship around and find other planets and a few fun things which might be mostly inside What if jokes. That’s it. This is a game. It’s silly and funny, and I prefer it.
However, it seems that even in a straightforward game you’ll be able to explore some key concepts in physics.
True orbits
One of the things you’ll be able to see on the primary planet is a recreation of “Newton’s cannonball” – Isaac Newton’s thought experiment on the connection between a fast-moving projectile and orbital motion. Newton said that when you were capable of fire a really fast cannonball horizontally from a really high mountain, it’s possible that the curve of its trajectory could match the curvature of the Earth. This would make the cannonball drop but never hit the bottom. (This is essentially what happens to an orbiting object just like the International Space Station, except the ISS wasn’t shot down from a high mountain.)
Seeing Newton’s cannonball, I assumed I could steer my spaceship into the orbit of this little planet, which could be fun. I attempted it immediately using the arrow keys – with little success. Each time I almost brought it right into a stable orbit, it didn’t last long. This made me wonder if the physical interactions that control orbits in What if world are much like those in the actual universe.
The first concept in physics to relate to orbital motion is, after all, gravity. There is a gravitational interaction between any two objects which have mass. For example, there’s a sexy force between the Earth and the pencil you hold in your hand because each have mass. If you let go of the pencil, it would fall.
If you’re standing on the surface of the Earth, the force of gravity on the pencil appears to be constant. However, when you take this pencil far enough away from Earth (for instance, 400 kilometers away, which is the gap the ISS orbits), you’ll notice a decrease within the gravitational pull: the pencil would weigh less and take longer to fall.
We can model the gravitational force between two objects with the next equation:
Illustration: Rhett Allain
