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Calrification on the physics of a car crumple zone.

  1. Oct 25, 2011 #1
    1. The problem statement, all variables and given/known data
    Consider the impact of a crash on the people inside a motor vehicle. What modifications can be made to a car to improve their safety. Describe the physics involved in the modifications.



    2. Relevant equations
    Assumedly Force = mass x accelleration.
    KE = 1/2 mass x velocity^2
    work = force x distance
    Conservation of energy.



    3. The attempt at a solution
    The first modification that crossed my mind was the crumple zone. I have a vague idea of how it works; the front of the car is designed to deform thus absorbing some of the energy. But I'm not sure of the specifics of the physics behind it. Does it work because it gives the car more time to reduce its speed thus reducing the decelleration. Does it work by increasing the reletive "distance" by which the force acts thus reducing the work/energy experienced by the part of the car where the passengers are. Does it work because the act of crumpling creates more heat and sound energy than if the front of the car were to stay intact therefore reducing the kinetic energy that acts upon the rest of the car.

    Any rough explaination as to where the energy actually goes/why the act of crumpling reduces the energy experienced by the passengers would be wholey appreciated.
    Thanks.
     
  2. jcsd
  3. Oct 25, 2011 #2

    Stephen Tashi

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    Science Advisor

    It takes energy to permanently deform materials (including people's bodies). So collisions do more than transfer kinetic energy to heat and sound. Conservation of energy should be a good argument why having the car body deform decreases how much human bodies inside it deform. However, energy is a rather crude approach to the problem. A person could be pushed by a 10 lb force for a long time without harm. Larger forces over shorter periods of time do damage. So I think "power" is a better thing to look at than "energy", but a textbook question might only expect you talk about energy, especially if that the subject being explained in the current chapter.
     
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