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Homework Help: Conservation of Impulse?

  1. Jun 29, 2010 #1
    Conservation of Impulse???

    1. The problem statement, all variables and given/known data

    I know that momentum is conserved, but is impulse???

    2. Relevant equations
    Impulse = change in momentum


    3. The attempt at a solution

    I really have no idea. I would say it isn't conserved because it equals the changein momentum. But the two options I can choose from are:

    Impulse is ALWAYS conserved or MOSTLY conserved in collisions...

    Any help would be great thanks. :D
    SO is it always or mostly??? *confused*
     
  2. jcsd
  3. Jun 29, 2010 #2

    kuruman

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    Re: Conservation of Impulse???

    When momentum is conserved, you have a system of two or more components which exchange momentum in such a way that, even though the momenta of all components change, the sum of the momenta remains the same. While momentum is transferred from one component to another, equal and opposite impulses act on the two objects as required by Newton's 3rd Law. So to recognize momentum conservation, one would have to record the system's total momentum before the exchange and compare with the system's total momentum after the exchange. If they are equal, momentum is conserved.

    Since you asked the question, what exactly do you mean by "impulse conservation"? How would you recognize impulse conservation if you saw it?
     
  4. Jul 1, 2010 #3
    Re: Conservation of Impulse???

    So Impulse = Force x Time
    By impulse conservation I mean, the product of the force applied and the time over which it is applied remains the same before and after the collision. And yet that would mean that the change in momentum of the objects would be the same. :confused:
    I don't know if you could actually see impulse conservation, unless the two objects had the same acceleration or something.

    Impulse is a concept that really confuses me. I really have no idea about what to say for this question.
     
  5. Jul 1, 2010 #4

    kuruman

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    Re: Conservation of Impulse???

    The impulse on one of the colliding objects is the total momentum transferred to that body during the collision. It can take the form of "product of force times time" and more correctly the area under the force vs time curve. Before the collision there is no impulse because the collision has not taken place. After the collision, the impulse is whatever momentum was transferred to one mass. It is equal and opposite to the momentum transferred to the other mass. As I said earlier, the fact that impulses come in pairs that are equal in magnitude and opposite in direction is not a conservation principle but a direct consequence of Newton's Third Law.
     
  6. Jul 3, 2010 #5
    Re: Conservation of Impulse???

    Ahh thanks heaps. Great explanation! :D Finally I understand this concept!
     
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