Bouncing Particles

About

There is a world with multiple randomly-placed, randomly-sized, stationary particles. There are butons to to play, step, and reset the model. stepping the model causes the particles to move. If a particle hits a wall, it bounces off.Reseting the model places the particles at new random locations with new random sizes. Playing the model, causes it to step repeatedly. Resetting the model causes it to stop playing. once the play button has been clicked, it cannot be clicked again until the model is reset.