When riding in a vehicle, you travel as fast as the vehicle does. If the vehicle stops suddenly, you keep going until something stops you.

It could be the windshield, the instrument panel, or the safety belts!

When you wear a safety belt, you and the vehicle slow down together.

There is more time to stop because you stop over a longer distance and, when worn properly, your strongest bones take the forces from the safety belts. That is why wearing safety belts makes such good sense.