a seat belt acts as a restraint when you get into a car accident. if something is in motion it will continue to stay in motion until it is stopped by something, in this case if your going 70 mph on the highway and you hit the brakes the car will stop because of the brakes and unless your wearing your seat belt your body will continue to go 70 mph until stopped by an object, maybe the dashboard or the wind shield that's why you must wear your seat belt at all times
