The ideal process of a seatbelt's function is as follows: First, it tightens immediately and without hesitation restrains the person into their seat at the very first moment of an accident. Then, it relaxes moderately after the peak of impact has passed or when the occupant is already protected by the airbag, thus appropriately loosening the belt to avoid rib injuries caused by excessive force. The most advanced seatbelts come equipped with pre-tensioners and force limiters; let us examine the functional principles of these two components.
1. **Seatbelt Pre-tensioner** - When an accident occurs, the occupant moves forward while the seat moves backward. At this point, if the seatbelt is too loose, the possible consequences may include: the occupant slipping underneath the seatbelt or the occupant coming into contact with the airbag while the seatbelt, due to excessive slack, fails to tighten in time. This means it does not absorb part of the impact as expected, but instead places the entire burden on the airbag. Either of these scenarios can lead to serious injury for the occupant. However, the question arises: where does the looseness come from in a correctly installed seatbelt? One reason is that the occupant's clothing itself contributes...