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Balls in a Box Model
written by Wolfgang Christian
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.
1 source code document is available
Subjects Levels Resource Types
Classical Mechanics
- Linear Momentum
= Conservation of Linear Momentum
- Newton's Second Law
= Interacting Objects
- Newton's Third Law
= Action/Reaction
Thermo & Stat Mech
- Kinetic and Diffusive Processes
= Approach to Equilibrium
- Lower Undergraduate
- Upper Undergraduate
- Instructional Material
= Interactive Simulation
Intended Users Formats Ratings
- Learners
- Educators
- application/java
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Access Rights:
Free access
Program released under GNU-GPL. Narrative is copyrighted.
This material is released under a GNU General Public License Version 3 license.
Rights Holder:
Wolfgang Christian
molecular dynamics, sensitivity to initial conditions
Record Cloner:
Metadata instance created November 16, 2008 by Wolfgang Christian
Record Updated:
June 2, 2014 by Andreu Glasmann
Last Update
when Cataloged:
November 15, 2008
Other Collections:

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Record Link
AIP Format
W. Christian, Computer Program BALLS IN A BOX MODEL, Version 1.0 (2008), WWW Document, (
W. Christian, Computer Program BALLS IN A BOX MODEL, Version 1.0 (2008), <>.
APA Format
Christian, W. (2008). Balls in a Box Model (Version 1.0) [Computer software]. Retrieved June 1, 2023, from
Chicago Format
Christian, Wolfgang. "Balls in a Box Model." Version 1.0. (accessed 1 June 2023).
MLA Format
Christian, Wolfgang. Balls in a Box Model. Vers. 1.0. Computer software. 2008. Java 1.5. 1 June 2023 <>.
BibTeX Export Format
@misc{ Author = "Wolfgang Christian", Title = {Balls in a Box Model}, Month = {November}, Year = {2008} }
Refer Export Format

%A Wolfgang Christian %T Balls in a Box Model %D November 15, 2008 %U %O 1.0 %O application/java

EndNote Export Format

%0 Computer Program %A Christian, Wolfgang %D November 15, 2008 %T Balls in a Box Model %7 1.0 %8 November 15, 2008 %U

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Citation Source Information

The AIP Style presented is based on information from the AIP Style Manual.

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