Crash Tests with Seatbelts
Seatbelts use two main ideas to protect passengers during a car accident. First, they slow the passenger down more slowly than the passenger running into steering wheel or dashboard. This keeps the force required to stop them smaller. (see impulse) It also prevents the person from contacting any of the glass windows in the car or continuing on to be stopped abruptly by the road, tree, or another automobile. The video clip above shows the role of the seatbelt during an accident.
Crash footage from the National Transportation Safety Board