I am a sucker for attention-grabbing on-line video games that do not have a rating or perhaps a purpose. On this case, it is a cartoon house simulator to advertise the e book What If? 2, by Randall Munroe, the writer of the xkcd comics.

You may play it by clicking here. (Don’t fear, I’ll wait.)

The sport works like this: You begin off with a rocket on a really small planet. Click on on the rocket to start out, then you need to use the arrows in your keyboard to activate the thruster, rotate the spacecraft, and discover different planets and some enjoyable issues which might be largely inside What If jokes. That is it. That is the sport. It is foolish and enjoyable, and I like it.

But it surely seems that you need to use even a easy sport to discover some key ideas in physics.

Actual Orbits

One of many issues you’ll be able to see on the preliminary planet is a recreation of “Newton’s cannonball”—Isaac Newton’s thought experiment in regards to the connection between a fast-moving projectile and orbital movement. Newton mentioned that in the event you have been in a position to shoot a really quick cannonball horizontally off a really tall mountain, it is potential that the curve of its trajectory may match the curvature of the Earth. This might make the cannonball fall however by no means hit the bottom. (That is basically what occurs with an orbiting object like the International Space Station), solely the ISS wasn’t shot off a tall mountain.)

Seeing Newton’s cannonball made me assume that I may get my spacecraft to orbit this tiny planet, which might be enjoyable. I attempted it straight away utilizing the arrow keys—with little or no success. Each time I nearly received it right into a steady orbit, it wouldn’t final. That made me surprise if the physics interactions that management orbits within the What If world are something like these in the actual universe.

The primary physics idea that applies to orbital movement is, in fact, gravity. There’s a gravitational interplay between any two objects which have mass. For instance, there may be a horny drive between the Earth and the pencil you’re holding in your hand, since they each have mass. Should you launch the pencil, it falls.

Should you’re standing on the floor of the Earth, the gravitational drive performing on the pencil appears to be fixed. Nonetheless, in the event you get that pencil far sufficient away from the Earth (like 400 kilometers away, which is the space at which the ISS orbits), then you definately would discover a lower within the gravitational interplay: The pencil would weigh much less and take longer to fall.

We will mannequin the gravitational drive between two objects with the next equation: