About
There is a world with one randomly-placed, randomly-sized, stationary particle. There are butons to to play, step, and reset the model. stepping the model causes the particle to move. Reseting the model places the particle at a new random location with a new random size. Playing the model, causes it to step repeatedly. Resetting the model causes it to stop playing. once the play button has been clicked, it can not be clicked again until the model is reset.