The force of impact is four times as great at 60 mph as it is at 30 mph. Here's why:

* Kinetic Energy: The force of impact is directly related to the kinetic energy of the car. Kinetic energy is calculated with the formula: KE = 1/2 * mv² (where m is mass and v is velocity).

* Doubling Speed, Quadrupling Energy: When you double the speed (from 30 mph to 60 mph), you are squaring the velocity in the formula. This means the kinetic energy (and therefore the force of impact) increases by a factor of 2² = 4.