The working of seat belts in cars is related to the law of Inertia in physics. Inertia refers to the resistance offered by an object in motion, to change the way it is moving. The law of inertia states that a body in motion preserves its speed and direction as long as no force acts on it and a body at rest will lay at rest unless a force acts on it to change its state of rest. Heavier the object, more is its inertia.
We experience inertia while travelling by cars, swinging in a swing, hitting a ball etc. While sitting in a car, the passengers or the things that are inside the car has got some inertia. When a car moves with a speed, passenger sitting inside the car also travels with the same speed. Imagine a fast moving car that stops suddenly or hits an object bringing the car to a halt. In that case, when a person does not wear a seat belt and car crashes coming to a halt, because of the person’s inertia he will still be moving at the same velocity at which the car was travelling and in the same direction. That’s why the person gets thrown at car’s speed in the forward direction.
We know that the use of seat belts ensures safety of the passengers. Imagine the above case but with the passenger wearing the seat belt. Now the seat belt provides enough opposing force to stop this forward motion of the passenger. Also the seat belt applies this force at the chest and pelvic region which is very strong.
Eyes and vision : Basics ought to be known.