This is a simple open source 2D physics engine for planets, atoms and other particles. The particles interact through force fields and collisions. The force fields have the forms 1/r^n, r^n and A/r^n - B/r^m. These fields can be used to i.e. simulate gravitation, harmonic oscillators, and the atomistic Lennard Jones potential. When the particles collide they merge, bounce or split into more particles. It is also possible for the particles to have negative masses. The idea is to make fun and interesting games using very simple physics. Start stop and reset a simulation by pressing the menu button.