Particle Physics Simulator is a free physics sandbox game available for Android. It offers a physics sandbox with n-body capabilities where the behaviour of the system is driven by each particle's gravity. You can adjust the gravity strength, the number of particles, the friction, or the collision policy to set your initial conditions and just watch the system evolve or intervene to decide the fate of the particles.

The game features n-body physics simulation with pure gravitational interactions between particles. You can create walls that particles can't trespass and watch them bounce off. There are collision policies, such as physically realistic elastic collisions, mergers, or no collisions at all. You can also customize particle colors, background image/color, gravity strength, particle masses, and sizes. Additionally, you can add friction to the mix, use accelerometer support, enable/disable the central black hole, and modify simulation velocity in real-time. There are also particle-particle and particle-mesh simulation methods, with the first for accuracy and the second for performance. Contact the developer for suggestions or bug reports.

Overall, Particle Physics Simulator is an excellent physics sandbox game for Android that offers a wide range of customization options and features. It's perfect for those who enjoy exploring physics concepts or just want to have fun watching particles interact with each other.