This appears to me to be a simple problem, but I am not a very big physics person- Though I do know that is the key to the problem... Short story is, my girlfriend was in a motor vehicle accident last week. She was just about stopped in stop and go traffic, and was impacted from behind, and driven into the car in front of hers, and the two moved into the car ahead of that, for a total of four cars involved. Here are the variables as I understand them: Temperature- about 85 Road condition- dry Weather- clear Assumptions: Tires(all cars) 50% tread All drivers, except car 1, applying brakes. Weights: Car 1(car at rear struck car 2) 2630lbs curb weight. We shall assume 2800 to be the total weight Car 2(mine) 3344lbs curb weight, we shall assume 3500lbs Car 3(forward of mine) 3329lbs, we shall assume 3500lbs Car 4(forward most vehicle) 2780lbs, we shall assume 2900lbs Positions: Car 4, at front of line, stopped Car 3, behind car 4, stopped, we shall assume typical spacing of about 5 feet Car 2, behind car three, almost completely stopped, we shall assume spacing of about 7 feet, diminishing Car 1, behind car 2, moving: we need to solve for its approximate speed & force. The order of impacts as I believe they happened are these: Car 4 and car 3 were fully stopped, as traffic forward of them had stopped. Car 2 had come to almost a complete stop, and car 1 impacted car 2 at an unknown speed. I believe car 2 was impacted in accordance with Newtons Laws of Motion, and was propelled forward,impacting and transferring the energy into car 3 which was propelled forward away from car 2. Car 2 was then struck a second time by car 1, a result of car 2's transfer of energy into car 3, (which caused car 2 to slow down) while car 1 remained in motion after the initial impact, which reduced its speed, but still had sufficient momentum to strike car 2 a second time. Car 2 was driven a second time into car 3(by the second impact from car 1), which continued forward into car 4, and all four cars came to rest at this point. What I would like to know is: 1. Does this theory- that the rearmost impacting car(1) caused the car it hit(2) to be propelled forward striking the car ahead of that(3) & then the initially struck car (2) stopped when its energy transferred into the one it hit(3), was then impacted a second time by the rearmost car(1), driving it into the back of the car(3) ahead a second time, and the group into the front car(4)- sound like a reasonably probable chain of events; 2. WHAT would the speed of the rearmost car (1) potentially have been to make such a series of events likely? 3. What was the FORCE of car 1 into car 2(first time); car 2 into car 3 (first time); car 1 into cars 2, 3, & 4? Sorry for a LONG question, but I was watching "Big Bang Theory" while I was formulating this. I simply want to find an answer, as we are having to go to court because the driver of car 3 claims my girlfriend's car(car two) struck them TWICE, so she has received a summons for "Careless Driving" !(And SHE was the FIRST ONE HIT!!!). I want to have a pretty good idea of what the exact physics were involved, and I think someone here may be able to help... :) Thanks! Scott They say ∏ r square. To me, ∏ r ∇∇∇∇∇∇ all neatly arranged in a circle, with the tips together... Until I eat one... After a while, ∏ r GONE.