What makes a seat belt so important a safety feature? It keeps people from being thrown around and out of the car.

When something is in motion, it stays that way until it hits an immovable object. Thus, when you ride in a car, the car isn’t the only thing moving—you are as well. If the car stops gently, you stop gently. When the car stops quickly, you keep moving and jerk forward and back. In most cases the car isn’t going that fast and you do not bounce around. But during a collision, the car’s motion changes, whether it stops moving forward or is pushed sideways. Yet even though the car stops, you keep moving. Without seat belts, the driver and passengers would bounce around the car, hitting surfaces such as the windshield and windows, the doors, the dashboard, and each other. Unrestrained people may even be thrown out of the car from the force of the impact. Being thrown from the car is a major cause of serious injuries and deaths in accidents.

The seat belt prevents this from happening by restraining your movement and holding you in place. You may end up with bruises from the seat belt, but these are minor compared with the injuries that would otherwise occur. Seat belts also work in conjunction with air bags. While the seat belt holds the driver or passenger in place, the air bag slows the movement of the driver or passenger with as little injury as possible. To do this, the air bag must inflate quickly, opening with explosive force. Seat belts keep drivers and passengers at an optimal distance from the inflating air bag, so that it does not cause other injuries