But the acceleration that you are concerned about here is the acceleration (or deceleration) of a car from it's current speed to the speed after the crash. That's the acceleration that has an impact on humans.

A more accurate equation to look at would be kinetic energy = 1/2mv^2. More energy a car has in hitting something the worse the outcome will be.

Now you can say that cars with greater acceleration may be more likely to be driving faster, but it's not a direct correlation of acceleration of a car to the force of impact of the car.

> A more accurate equation to look at would be kinetic energy = 1/2mv^2. More energy a car has in hitting something the worse the outcome will be.

worse it will be for who, for people in the car or for the something?

it's kinetic energy that matter at the impact. def: E=mv^2/2

assuming car 2 is 2x heavier than car 1, to have the same kinetic energy, their respective velocities should be: m2 = 2 * m1 2m1 v2^2/2 = m1 * v1^2/2 2 * v2^2 = v1^2 v2 = v1/sqrt(2) ~ 0.7

another word 2000lbs car driving at 100mph has the same kinetic energy as 4000lbs driving at 70mph