# re Re: crash tests

OK, youse guys, you need to consider both momentum, and energy, and
stiffness of the objects colliding.  Assuming the vehicles deform and stick
together:

Case 1:  Frictionless surface.
Case 1a.  Both cars going 30 mph.  Momentum of each is mv with
opposite signs.  Final momentum has to be zero.  Energy of each is 0.5mv^2.
All this energy is dissipated into the bodywork for a total of mv^2, of
which one half goes to each.

Case 1b.  One car 60 mph, the other 0 mph.  Momentum of the first is
2mv, momentum of second is 0mv.  Final momentum is 2 mv, with both masses
stuck together and traveling at 30 mph.  Total energy initially is
0.5m(2v)^2, final energy is 0.5(2m)v^2.  Thus 0.5mv^2 has been dissipated
into each vehicle, same as above.

Case 2:  Infinite friction surface.
Case 2a.  Both cars going 30 mph.  This is effectively the same case
as above for soft structures.

Case 2b.  Initial momentum and energy is the same as case 1b.  Final
momentum is zero, so all of the 0.5m(2v)^2 enegy is dissipated into the
collision and the vehicle see twice the destruction as in case 1b.

For cases where the vehicles are infinitly stiff and bounce off one another
like billiard balls, momentum is reversed and no energy is lost.  The
occupants, however, have been subjected to very high g's and are squished.
Vehicles are generally built to avoid this.

kirby