What is the actual physics of a car crash, and its involvement with the crumple zone, safety belt, and air bag

Question

Of course I know that a seat belt and all that would prevent further harm to the driver / passenger. I'm curious about the complete physics of a car crash.

Answer 1

The "the complete physics of a car crash" would be a very long and complicated answer.
However, the specific items you mention (crumple zone, safety belt, air bag) all serve a common purpose in the event of a crash...to lessen the force which is applied to the car/passengers/... at any given in the event off a crash.

Imagine you are in a car driving at 60 mph and you run into a solid brick wall. One way or another, the car and its contents are going to stop. The faster the stopping action happens, the larger the force acting on the car and the more harm can be done. If the crash / stopping action occurs very quickly, the change in the overall object's momentum occurs very quickly and results in a large force. But if you slow down the crash, even for a few fractions of a second, it can significantly reduce the instantaneous force acting on the object, even though the overall impulse applied to the object is the same.

By using crumple zone, the car "crumples" as it hits something, which slows down ow fast the car comes to a stop. Using a safety belt and air bags work in a similar fashion to slow how fast a passenger comes to a stop by cushioning the impact.
The more effective "padding" is used, the smaller the force experienced by the object. Think of it like an falling onto a concrete floor versus falling onto a pillow. The pillow "gives" more on an impact whereas the concrete floor doesn’t move much at all and the impact happens very suddenly. An eggs will almost certainly break if hitting a concrete floor, but stands a good change of survival if it falls onto a pillow thus illustrating the lessening of the instantaneous force acting on the object even though in both cases the result is the same...the egg comes to a stop.

Answer 2

For those who do not put on a seatbelt, which you could jerk ahead in a crash or a brief discontinue, the air bag stops you from jerking forward and hitting into the glass or whatever, they each can save your existence. If you are shorter, you would get sufficated via the air bag, which is why kids underneath 12 have got to sit in the back seat, where there is no airbag. It's a law to wear a seat belt-- you would get arrested. I'd advocate carrying one- it only helps you.