MythBusters - Crash Force - awesome test
 

Video - MythBusters - Crash Force

Mythbusters crew decided to revisit an old myth that was drawing the ire of the show's fans for quite some time. And it's sure to be an interesting topic to automotive enthusiasts.

When two cars collide, each traveling 50 miles per hour, does the resulting force equal one car hitting an immovable object at 100 miles per hour?

It seems like such simple physics, no? But don't forget Newton's third law. To quote the great Wikipedia of knowledge, "Whenever a first body exerts a force F on a second body, the second body exerts a force −F on the first body. F and −F are equal in magnitude and opposite in direction." Or, more simply, for every action there is an equal and opposite reaction.

remember force and energy are different things... F = MA, and E=MV^2
So one car @ 100 into a wall is twice the force of one car into another at 50 - since a head on collision is 'nearly' identical to hitting a wall since both come to a dead stop.

The energy is a squared, so 100 into a wall is 4x of hitting another car at 50.

If you listen to the original episode, I think jamie's comment said force - which is correct... and they tested based on the comment being energy, which would not have been correct.

It's a cool episode - car crashes and such, it's online if you search.