Crumple Zone
The crumple zone is a very important part of vehicular safety. If you do get in a crash, the crumple zone of the car works to create a larger stopping distance and time. As you have already learned, the longer the stopping distace/time, the less force that will be exerted on your body. A car with a rigid frame will come to rest MUCH quicker than a car with a good crumple zone. Since the same impulse is needed to stop the passengers as it takes to stop the car, a passenger in a rigid framed car will likely a tremondous force and suffer devastating injuries.
In the Following video, observe how the front end of the car crumples, while the rest of the car remains fairly intact.
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Metal Frame
While it is paramount that a car have a good crumple zone, it also needs to have a strong metal frame. The crumple zone slows the stop of the car, but it is the metal frame which keeps the occupants from being crushed by the collision. If the metal frame is weak, it could crush inwards, literally crushing the passengers with it.
Seatbelts and Airbags
Knowing what you now know about physics, why do you think it is important to wear a seatbelt and have working airbags?
Well, both seatbelts and airbags help slow your body down in a crash. Without them, the only thing to slow your body down would be the dashboard of the car or the windshield as you fly through it. Yes, the crumple zone does lessen the deceleration, but what good will that do you, if you aren't attached to the car in some way. Remember, your body wants to stay in motion. Wearing a seatbelt is the only way to guarantee a more gradual stop in a high speed collision.
Watch the following video, keeping in mind what you have already learned.
Did you notice that the dummies continued to move forward, without the car, until their seatbelts restrained them? A good working seatbelt, could really be the difference between life and death in a collision.
Safety of the Future
Many advances are being made in the safety department of car advancement. However, the focus of safety features is now on avoiding collisions to begin with. You can actually read about three of the newest safety developments, which serve to avoid crashes, at USAToday