Formation of clusters due to inelastic collisions

Role of inelasticity in granular medium

If your browser is enabled for Java, the following applet will demonstrate the role of inelasticity on the velocity and density distribution of a simulated one dimensional gas. The particle on the right gets a random velocity when it collides with the right wall.

There are two relevant parameters that may be adjusted:

The coefficient of restitution r, which is the fraction of the initial kinetic energy that remains after a collision (Red bar, Drag mouse to change).
The number of particles N (Gray bar).

The particles cluster near the left wall as r is decreased. You may also observe "inelastic collapse" (an infinite number of collisions in finite time) for small r.

The theory is from Y. Du, H. Li, and L.P. Kadanoff Phys. Rev. Lett. (1995).

The program written in Java using JDK 1.1. The advantage of an applet is that it is interactive. Move the bar on the top right to change r. Besides changing r and N, and the Reset button, you may also stop and resume the program by clicking on the black background.

Source code for the applet and program details.

Recently we have done experiments that reveal similar phenomena in a quasi-two dimensional system. See A. Kudrolli, M. Wolpert, and J.P. Gollub Phys. Rev. Lett. (1997).

Sites we found useful in developing this program:

Some Java programs can be found here.
comp.lang.java FAQ, contains a good introduction and summary.

For information on the program contact

Arshad Kudrolli,

Department of Physics
Haverford College
Haverford, PA 19041

last updated 2/18/97.