This is a very abstract example simulating the kinetics of a set of N " perfect " rigid bodies with random initial masses and velocities. The behavior of a Particle is composed of two simple basic behaviors : Inertia and Bounce. We can just add a generation of the event " energy " to this program and trace the value of global kinetics energy of the system using the listener component EnergyTracer. Thus the event based model provides us simple and modular way to get all data and graphical representation of all dependencies during a simulation.