Explain how the law of inertia relates to seat belt safety

Law of inertia will prevent movement of any object until unbalanced force act on them. When seat belt is put used, the movement of the body is limited, so when an unbalanced force, eg car crash acts on the body, it moves. Seat belt will prevent it.

Also, Seat belts stop you tumbling around inside the car if there is a collision. Upon sensing a collision the seat belts lock in place. When the car crashes, there is no unbalanced force acting on the person, so they continue forward (Newton's First Law). The person moves against the seat belt, exerting a force on it. The seat belt then exerts a force back on the person (Newton's Third Law). This causes a controlled deceleration of the person involved.