I've been sitting here thinking about collisions, deceleration, and conservation of momentum, and I just want to see if I'm on the right track. For a start, let's say we crash a car into a solid, "unmovable" wall at 50 mph, and measure the results. If we then take two cars identical to that first one and crash them into each other in a head-on collision, each traveling at 50 mph, the result should be the same--both decelerate in the same amount of time as if they'd hit an invisible wall. From there I started to wonder how this would look with a little relativity thrown in. A person in one of the cars should be able to claim that they're not moving and that the other car is coming towards them at 100 mph instead. The next logical question seemed to be whether a car going at 100 mph and crashing into an identical, stationary car would produce a practically identical result. This seems to make sense to me--car A, going at 100mph, should push car B as it hits it, probably causing both cars to now be moving in the direction car A was moving at closer to 50 mph than 100 mph. If that's right then the acceleration/deceleration felt by the two drivers should be roughly the same as the 50/50 head-on collision. Each car's speed would have changed by a factor of 50 mph. Am I thinking about this the right way? Would the damage to each car be similar in all three of these examples, and would the forces felt by the people inside these cars actually be similar as well? Thanks for any thoughts.