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Elastic vs inelastic collisions formulas

  1. Jul 8, 2013 #1
    When doing practice problems from my textbook, I often get confused with both of them.
    MOre specifically there are usually formulas which pertain to only one of those types of collisions.

    Ex: [itex] (v_1-v_2)_i = -(v_1-v_2)_f [/itex]

    Does anyone know more of these types of formulas, or tricks to solve these equations?

  2. jcsd
  3. Jul 8, 2013 #2


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    2016 Award

    Staff: Mentor

    Sure, your textbook.

    - you can always use momentum conservation
    - in elastic collisions, you can use energy conservation in addition
    - in perfectly inelastic collisions, the objects stick together afterwards, so they have the same velocity
    - in the center of mass system, all those collisions are easy to study

    All equations are just a result of those ideas.
  4. Jul 8, 2013 #3
    Elastic collisions: KE is conserved, momentum is conserved
    Inelastic collisions: KE is not conserved, momentum is conserved.
    This is a reasonable starting point
  5. Jul 8, 2013 #4
    Also, don't be confused by the word "elastic." In common usage, "elastic" is like a rubber band or a balloon, that is, something "stretchy." BUT, when we say "elastic collision" in physics, examples are hard steel ball bearings (like you see in a Newton's Cradle toy) or billiard balls. Collisions of soft stretchy things (like soft rubber balls) are likely to be "inelastic." Confusing? I thought so when I learned this stuff the first time.
  6. Jul 9, 2013 #5
    elastic collision

    if masses of two objects is same than in elastic collision there velocities get interchanged and if masses are not equal than you can use the formula which u have given for elastic collision.
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