without these, when braking hard you will keep moving and not decelerate, causing to fly through the windshield
these strap you in, but also stretch under large forces
stretching increases the distance moved slightly, but extends the time taken more for passengers to stop
this decreases the rate of change of momentum and therefore reduces the force
Crumple zones:
Without these, the car would be a solid metal block, which would immediately stop during a crash instead of "softening" the blow slightly
"softer" areas at the front of the car, which crumple upon a crash
It absorbs energy to deform and compact
It increases the time taken for the car to stop
This reduces acceleration and force on passengers
Air Bags:
Without these your head will whip forward during a crash, hitting the steering wheel or whipping back to hit the back of the head, which would cause serious neck energy
These inflate instantaneously upon a crash
Your head hits this and slows down
Increases the time taken for the head to stop moving