Collisions (momentum)

[Henry Kuhlman <hk@SOUTHERN.EDU>]

Every collision between two particles, A and B, is characterized by the
coefficient of restitution, e.

          e = (vBf-vAf) / (vAi-vBi)

e = 1 is a completely elastic collision, kinetic energy is conserved.

e = 0 is a completely inelastic collision, A and B stick together.

0 < e < 1 is all "real" collisions.

A particle of mass m traveling at v and having a head-on
collision with an identical particle of mass m traveling in the
opposite direction at v has a certain value of e;
which is the same as the value of e for the same
particle of mass m traveling at v and making a head on
collision with an infinitely massive particle at rest.



> In the Cover Story of the Wed 30 June 99 USA Today, Edward Moeller, a
> traffic engineer is quoted, "If you are driving 35 and hit someone coming
> at you at 35, it's the equivalent of hitting a tree at 70."


This quote is ALWAYS wrong (for ANY value of e).

If 70 is changed to 35 the quote is ALWAYS correct (for ANY value of e).

A factor of two seems important.


hk@southern.edu