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Ejs Hard Disk Collision Model
written by Wolfgang Christian
The Ejs Hard Disk Collision model displays a two-dimensional collision between two hard disks.  The two disks have the same mass and only one mass is moving at the beginning of the simulation.  The impact of the collision is offset by the impact parameter, b, which can be changed.  The center-of-mass of the two masses is also shown.  You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting "Open Ejs Model" from the pop-up menu item.  

Ejs Hard Disk Collision 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_newton_HardDiskCollision.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 Newtonian 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 (JRE).
Subjects Levels Resource Types
Classical Mechanics
- Linear Momentum
= Collisions in Two Dimensions
= Conservation of Linear Momentum
- Motion in Two Dimensions
= Center of Mass
- Lower Undergraduate
- Instructional Material
= Activity
= Interactive Simulation
Intended Users Formats Ratings
- Learners
- Professional/Practitioners
- Educators
- application/java
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Access Rights:
Free access
© 2008 Wolfgang Christian
Additional information is available.
Easy Java Simulations, Ejs, OSP, Open Source Physics, center of mass, classical mechanics, collision, conservation of momentum, modeling
Record Creator:
Metadata instance created July 5, 2008 by Mario Belloni
Record Updated:
June 5, 2014 by Andreu Glasmann
Last Update
when Cataloged:
July 1, 2008
Other Collections:

ComPADRE is beta testing Citation Styles!

Record Link
AIP Format
W. Christian, Computer Program EJS HARD DISK COLLISION MODEL, Version 1.0 (2008), WWW Document, (
W. Christian, Computer Program EJS HARD DISK COLLISION MODEL, Version 1.0 (2008), <>.
APA Format
Christian, W. (2008). Ejs Hard Disk Collision Model (Version 1.0) [Computer software]. Retrieved October 22, 2017, from
Chicago Format
Christian, Wolfgang. "Ejs Hard Disk Collision Model." Version 1.0. (accessed 22 October 2017).
MLA Format
Christian, Wolfgang. Ejs Hard Disk Collision Model. Vers. 1.0. Computer software. 2008. Java (JRE) 1.5. 22 Oct. 2017 <>.
BibTeX Export Format
@misc{ Author = "Wolfgang Christian", Title = {Ejs Hard Disk Collision Model}, Month = {July}, Year = {2008} }
Refer Export Format

%A Wolfgang Christian
%T Ejs Hard Disk Collision Model
%D July 1, 2008
%O 1.0
%O application/java

EndNote Export Format

%0 Computer Program
%A Christian, Wolfgang
%D July 1, 2008
%T Ejs Hard Disk Collision Model
%7 1.0
%8 July 1, 2008

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Citation Source Information

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

The APA Style presented is based on information from APA Electronic References.

The Chicago Style presented is based on information from Examples of Chicago-Style Documentation.

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