This is a gravity simulator. It's not very good. I don't know a lot of math.
Maybe it would be better if you imagined this with cubes. Bouncy cubes. Floating on bouncy water.
Or they have really tiny wheels. The circles are round because originally they were planets.
That's why this is called "Gravity". Because the circles themselves had gravity.
Anyways, you know Angry Birds? How you pull back on them and they move when you let go?
You can play with the imaginary cubes like that.