For a car crash with 90 km/h (25 m/s) the de-acceleration will be 64 times gravity (same parameters as above). Note that the National Highway Traffic Safety Administration (NHTSA) states that "the maximum chest acceleration shall not exceed 60 times gravity for time periods longer than 3 milliseconds". The impact creates a force 28 times gravity!!Ī person sitting inside the car with seat belts on will de-accelerate with a force 28 times gravity. Note that the gravitation force (weight) acting on the car is only The front of the car impacts 0.5 m (the deformation distance).į max = 1/2 (2000 kg) (16.7 m/s) 2 / (0.5 m) Example - Car CrashĪ car with a mass of 2000 kg drives with speed 60 km/h (16.7 m/s) before it crashes into a massive concrete wall. Note! - The deformation slow-down distance is very important and the key to limit the forces acting on passengers in a car crash. The deformation slow-down distance can be calculated as The average impact force can be calculated as In a car crash the dynamic energy is converted to work and equation 1 and 2 can be combined to In an impact where the object is not deformed - the work made by the impact force slowing down the moving object equals to the work done by a spring force - and can be expressed asį max = maximum force at the end of the deformation (N, lb f) When a crumple zone deforms in a car crash the average impact force is designed to be as constant as possible. S = deformation distance, crumple zone (m, ft) In an impact - like a car crash - the work made by the impact force slowing down an moving object over a distance by deforming the crumple zone can be expressed asį avg = average impact force during deformation (N, lb f) The dynamic kinetic energy of a moving object, like a falling ball or a driving car, can be expressed as
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