Many automobile passengers suffer neck injuries when struck by cars from behind. How does Newton's law of inertia apply here? How do headrests help to guard against this type of injury?

Jul 2, 2016

$\textcolor{g r e e n}{\text{NEWTONS LAW OF INERTIA}} :$

If a body is at rest or moving with constant velocity, then it will continue to be in rest or move with constant velocity unless an outer force acts on it.

Explanation:

You might have noticed while sitting in the car when ever the car moves from the rest (or accelerates) , it seems like some force is pushing us towards the seat back (OR you are being dragged in your seat.)

AFTER A WHILE you feel normal when the car's speed gets stable (at a constant speed.)

This to say your inertia first tried to make you in the rest but your seats resisted that phenomenon. And when you stared to travel with constant speed (velocity), then there is no net change in the acceleration i.e. acceleration becomes ZERO .

$\textcolor{b l u e}{\text{FINALLY ANSWERING YOU QUESTION;}}$

Similar is the case, when the car is struck from behind. The car suddenly accelerates and you are dragged in your seat. While your neck also feels the shock but is supported by the headrest.

{This is the inertia that first tries to get you in the rest when your car speeds up (accelerates) and you are pushed in your seat.( meaning to say when you were slow and car was fast.

now I think you will also be able to think of why we are pushed forward when the brakes are applied.