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Co-efficient of restitution

  1. Sep 10, 2013 #1
    Why is it that the co-efficient of restitution is given by

    (Va - Vb)/(Vb - Va) and not (Va - Vb)/(Va - Vb)?
     
  2. jcsd
  3. Sep 10, 2013 #2
    Depends much on how you decide to orient the reference system... anyway pay attention that initial velocities and final velocities are not necessarily equal, therefore you have better using different notations (like Va and Vb for initial velocities of the two objects and Ua and Ub for final ones)... indeed in your notation the second case you wrote would give you one no matter what happens...
     
  4. Sep 10, 2013 #3
    But why do I use the Va- vb and then in the denominator use Ub-Ua?
     
  5. Sep 10, 2013 #4
    http://en.wikipedia.org/wiki/Coefficient_of_restitution

    As far as I understand, you want to have a number between 0 and 1 (0 being the case in which one object stops, 1 being elastic collision)... then you have to do the ratio of the final relative velocities and initial relative velocities... this order is simply used to get two positive numbers... you could also put absolute values and get the same result with any order...
     
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