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Rigid Body Collisions

  1. Aug 24, 2008 #1
    Hello, I am new here, so I don't know if this is the right place to post this question or not, if not please move it to the right place.

    At the moment I am working on making a computer simulator for rigid bodies using java, the only problem is that I thought that high school physics would cover 2D collisions of rigid bodies, but it didn't. I am working purely in 2D, but as of now I am completely unfamiliar with calculus, and the only equations I can find use calculus. So far I only have 1 square that rotates at a fixed rate, as I don't know the angular acceleration and torque formulas (stupid calculus I start this year), and moves along the X axis and Y axis (plural of axis is what?). Right now I just want it to bounce off of the borders of the window properly, then I will progress to 2 square interacting. I have collision detection, just not reaction. I know I have a lot to learn, I don't need programming help, just the physics behind the programming (if I do need programming help I am also a member of a programming forum, but they don't know physics).

    thanks for reading, help is appreciated
  2. jcsd
  3. Aug 25, 2008 #2
  4. Aug 25, 2008 #3
    Patience! This is not an instant response forum.
  5. Aug 25, 2008 #4
    well, you responded pretty quickly
  6. Aug 25, 2008 #5
    2D collision is well-covered in all game programming books and it is not so useful to summarize everything here. It is better that you start reading some references and maybe later post some specific doubts.

  7. Aug 25, 2008 #6
    any specific free online references, (not wikipedia) that you recommend? ( i have no money for books, as i need to get my college texts )
  8. Aug 26, 2008 #7


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    What about:



    I'm just guessing - haven't the faintest idea how to solve your problem. But overall you may like to know that there are two ways to approach the problem:

    1) Newton's laws of motion. Basically you apply to every body in your system:
    force = mass x acceleration
    torque=moment of inertia x angular acceleration
    conservation of energy
    conservation of linear momentum
    conservation of angular momentum

    2) Lagrangian approach. This is a reformulation of Newton's laws, but in a way that constraints are easily implemented. A constraint is, for example, a rigid body. The particles in the rigid body are not free to move in any way - they must always maintain the same position relative to each other.
  9. Aug 26, 2008 #8
    HS physics covers everything you need to know to write your program. You should not need any calculus and I imagine you would want to stay away from it using Java and all.

    F = m a
    M = I alpha
    m1 v1 = m2 v2
  10. Aug 26, 2008 #9


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    Last edited: Aug 26, 2008
  11. Aug 26, 2008 #10
    my HS physics covered only 1D momentum problems, no 2D and no rotation, i get 2D i can do plane reflections, it's rotation that looses me :(
  12. Aug 27, 2008 #11


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    Yeah, I hate rotations too. Well, take heart, even MythBusters failed their rotation test. Balls rolling without slipping on balls rolling without slipping. No answers, just my sympathies - it'll take time to work out, but you'll get good at it. Maybe start from simple situations, like a playground see-saw for which you know what a sensible answer is.
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