The Balls in a Box model shows that a system of particles is very sensitive to its initial conditions. In general, an isolated system of many particles that is prepared in a nonrandom configuration will change in time so as to approach its most random configuration where it is in equilibrium. This model explores what happens if the initial conditions are chosen in a very special way.

The default initial condition corresponds to eight stationary particles perfectly aligned on the x-axis. Two particles approach from the left and the right and collide with the aligned balls. The Ejs model solves Newton's second law of motion numerically, pauses when a collision is detected, applies conservation of energy and momentum to the collision, and then the simulation is resumed. Small changes in the initial conditions of the system can be made to explore the sensitivity of the motion to perturbations.

The Balls in a Box model was created using the Easy Java Simulations (Ejs) modeling tool.  It is distributed as a ready-to-run (compiled) Java archive.  Double clicking the ejs_sto_BallsInBox.jar file will run the program if Java is installed.  Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models.  Additional Ejs models for classical mechanics are available.  They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Please note that this resource requires at least version 1.5 of Java.