You have to enter the initial velocity in the edit fields on top, click the "start simulation" button and see what happens. To have your planet move upwards you have to enter a negative value in the second field. The maximum velocity is "500" in any direction, the minimum velocity is "-500". Sometimes it *does* get complicated. Be aware that with a negative horizontal velocity you'll lose at once. The planets are spread by random if you reload the page. If you have won or lost and click the "restart" field the game will be restarted without new planets.
Click here to start the game.
This game does not work with the Internet Explorer, it's just tested with Firefox.