A: first point is the car/vehicle experiences a DeltaV/Impact speed change
the occupant experience a impact speed change/deltaV
depends on the impact configuration, distance to something to strike (dashboard, airbag, seatback, etc)
For a rear impact:
- 1st issue is the neck response to the movement of the torso/seat forward...the distance to the headrest is an important factor
- 2nd issue: seat strength...did it yield? and if so, how much?
- There has been much discussion of seat stiffness since if too stiff, you snap the neck, if too soft, the seat may yield enough that the occupant travel into the rear compartment (of course depending on the magnitude of the vehicle impact speed change)
Generally the impact DeltaV of the main collision event is also experienced by the occupant (the 2nd impact) as it strikes the interior, etc,
- if the vehicle run out includes irregular terrain, other object impacts, etc it also may include issues for the occupants.