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Physics and Car safety
The use of Headrests in a Collision

Headrests are found in every type of car to prevent neck injuries that occur during an automobile collision. The way the neck becomes injuried is due to physics.
 
- In some collisions when the car slams into another object or the brakes are slammed on very quickly the body stays in the same position but the head is thrown either backwards or forwards. Once the head is thrown one way it naturally is thrown the other way because the neck muscles and vertebrae force it that way. As the neck is thrown in the second direction it goes at a higher speed then when it was thrown in the first direction due to Newton's Laws.
 
Real Life Situation
Picture a person that is standing still getting pushed forward by another person. What are the effects? As the person pushing goes towards the second person they are going at a certain speed while the second person is not moving. As the person pushes the second person they seem to remain in almost the same position, taking only a step forward but their head goes backward and then forward. They may complain about their neck being sore for a while.
 
 Now picture that a car is going at a certain speed (which would be a lot faster then was the person was going at above) and it hits into a parked car with a person in it. The person in the second car would have neck injuries due to the impact if their headrest was not in place right. The person in the first car may also experience neck injuries because they are travelling at a certain speed and then quickly stop due to the collision, sending their neck forward with the same results as the person in the second car.
 

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Source:http://www.garageboy.com/fahrt/headrest.html
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