PURPOSE: The job of the seatbelt is to hold the passenger in place so the passenger is almost
part of the car which prevents the passenger from flying forward as the car stops abruptly in the case of a collision.
Real Life Situation
When a car stops suddenly due to a collision with another
object such as another car, a tree, pole, guardrail, etc. the car's acceleration decreases very
quickly in a short period of time. This is called deceleration. Newton's Law of Inertia explains how this happens.
LAW OF INERTIA: An object in motion continues in motion with the same speed and direction unless
acted upon by an unbalanced force.
As the car collides with another object, the other object provides the force
which changes the speed and direction. The
car stops going in the direction it was going in, and in some cases bounces back depending how hard of a force hits it or
how much momentum the car had. Also, the speed decelerates quickly due to the impact.
When all this happens the passenger is not being acted upon by a force to slow
them down. This part is where the seatbelt comes into play.
As the person continues in their same direction and speed ( forward and the same
speed that the car was going) the seatbelt catches them, holding them back from flying through the air.
The alternative is to not wear a seatbelt, but a force will still have to act on
the person in order to slow them down. This force will come from the dashboard or windshied as the person crashes into it
causing a lot of damage to themselves.
- A seatbelt has two parts. The first part rests over the passengers pelvis and the second part
rests over the shoulder and across the chest. When the car stops abruptly the seatbelt applies the stopping
force across a large section of the body so the damage is reduced.
- Seatbelts are made of flexible materials which have more give then a dashboard or
windshield would have.
- Since seatbelts are flexible one might ask how do they hold you in place? Seatbelts are designed
so that the machinery behind them tightens up the belt to hold the passenger in place when the car decelerates quickly.