>>5942875
The loose items in the car fly forward because of a transfer of energy.
Inertia is a resistance to that transfer, in either direction.
An object continues to move forward in defiance of a force acting to stop it because of inertia, but an object at rest also resists beginning to move when some force is applied to it.
This is the basis of Newtons Laws of Motion.
An object in motion stays in motion and an object at rest stays at rest unless acted on by an outside force.
The tendency to stay in whatever state the object is in is its inertia.
The objects that did not fly forward remained stationary because their inertia was greater than the energy imparted to them by the impact.
If the car had been moving forward and then came to a sudden stop the loose items in the car would then continue to move forward if their inertia would have overcome the friction trying to transfer their forward momentum into what they were sitting on.