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Homework Help: How does KE get changed into internal energy?

  1. Feb 23, 2006 #1

    How does macroscopic kinetic energy KE get transformed into internal energy?

    Car bumps into trash can and small dent is made in the car.Dent is caused
    by force from trash can over certain distance (i.e. car gave part of its KE to trash can and trash can gave part of its KE back to car, which transformed it into internal energy)?

    How did this transformation happen?I know if we try to deform a body a net force is created on atomic level that resists external force trying to deform a body even more.
    But if I'm not mistaken that act alone doesn't change internal energy?
    So what does?

    Same question for situation when friction changes KE of a body into internal energy. How exactly do molecules gain speed and thus gain internal kinetic energy?

    thank you
  2. jcsd
  3. Feb 23, 2006 #2


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    Staff: Mentor

    On the dent part, think of the analogy where the object being hit has a spring protruding and a ratchet mechanism to hold the spring at any compressed length. As the car hits the spring and compresses it, the spring ratchets in some and then stays at some compressed length. The conversion in energy has been from the car's drop in KE to the spring's increased PE. The increased PE of the spring can be considered internal energy for the thing that the car ran into.
  4. Feb 24, 2006 #3

    And how does friction get transformed into thermal energy?
  5. Feb 24, 2006 #4


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    Science Advisor
    Homework Helper

    The directed energy of an impact can become randomized at the atomic/molecular level by scattering.
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