Forces on the Body

   
http://autos.msn.com/research/vip/safety.aspx?year=2012&make=Nissan&model=Altima&trimid=-1

   A passenger that weighs 100 lbs (~45 kg) going 45 mph (20 m/s) in a car that hits a wall with an impact time of 0.1 secs will experience what amount of force?


            a=(20m/s)/0.1 s = 200 m/s²
           
           F=ma= (45 kg)(200 m/s²)= 9000 N

     This is approximately 2000 lbs of force exerted on the person. As I mentioned earlier seat belts and crumple zones help lower this amount of force but there is still a significant amount of force applied on the body.

    Car collisions can cause shear forces on the spine. A shear force is equal and opposite forces applied to the opposite side. In the spine it is when one part of the spine moves one way and  the other part moves another.
 
http://spinalstenosis.org/blog/spinal-stenosis-car-accidents/
    
   There was a study done to see the effects of the car seat forces onto the spine. "The direction and strength of the forces suggests the the car seat rapidly accelerates into the occupant's spine, causing the thoracic and lumbar curves to straighten...They found that the car seat exerted about 1500 N (approximately 337) of force, in a fraction of a second."  (Holcombe)