Anybody looking into the physics of 2D and 3D- elastic collisions may also be interested in my pages http://www.plasmaphysics.org.uk/collision2d.htm and http://www.plasmaphysics.org.uk/collision3d.htm which represent direct and general solutions of the problems. I have also written corresponding Fortran and C++ codes for this ( see http://www.plasmaphysics.org.uk/programs/coll2d_for.htm , http://www.plasmaphysics.org.uk/programs/coll2d_cpp.htm , http://www.plasmaphysics.org.uk/programs/coll3d_for.htm , http://www.plasmaphysics.org.uk/programs/coll3d_cpp.htm ) which are free to use for everybody.

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Note that there was a bug in the collision detection routine of the 2D-versions of my programs (this led in certain cases to collisions being detected when in fact there were none). I have corrected this now. I have also made minor changes to the code in order to improve speed. Furthermore I have added a simplified version to the 2D-routines that does not not contain the collision detection routine but just returns the new velocities assuming that the input coordinates are already those of the collision.

Thomas, 11.Dec.05

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Please note that I modified the code in my routines now such as to work for (partially) inelastic collisions as well. This was simply achieved by subtracting the velocity of the center of mass from the final velocities for the elastic collision case, multiplying this by the restitution coefficient (which is an additional input parameter) and adding the velocity of the center of mass on again.

Thomas