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Homework Help: Collision Question

  1. Nov 8, 2011 #1
    1. The problem statement, all variables and given/known data

    I have a question about a one dimensional collision lab done in class. We set up an air rail with two gliders..one at each end. Each glider had a rubber band bumper. We pushed them towards each other and they hit each other and bounced back some. We collected our data..see attachement.

    2. Relevant equations

    see attached

    3. The attempt at a solution

    The question that goes along with this collision is - is this an elastic collision?

    Looking at the data I would say no. I am confused however because perfectly elastic, inelastic and elastic collisons should not show a loss of momentum. So I think we must have done something really wrong when we collected our data. Any thoughts?

    thanks much

    Attached Files:

  2. jcsd
  3. Nov 8, 2011 #2

    Simon Bridge

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    Rubber bands huh?

    Your data shows it was an inelastic collision all-right. Rubber bands are good for this. The word "elastic" used by the manufacturer is just marketing - elastic bands are not all that elastic, they are just stretchy.

    Where do you think the energy and momentum went?
    Did the bumpers go "twang"? Did they heat up?

    Here's another experiment for you:

    Get a bunch of rubber-bands and join them together so you get one long one.
    Suspend it, add weights in even increments (I've done this with 4 bands and 20g washers) and graph the stretched length against weight added.
    (predict, before you do, what the shape of the graph will be.)

    When you run out of ruler, reverse the process - take weights away, and plot the length against weight as before. (usually you want 20-40 reading total.)
    (predict: before you do, what path do you expect the graph to follow?)

    Comment on the curves you get.

    If you've not done it - do it. You can do this at home.
    I count this experiment as essential for learning physics.
  4. Nov 8, 2011 #3
    Thanks for the response.

    So what your saying is the rubber bands absorbed the momentum? So the momentum was preserved in the rubber bands? Since they did go twang (stretch)? Im guessing not much heat was generated during the twang. So energy was lost during the stretch(deformation)?
  5. Nov 8, 2011 #4

    Simon Bridge

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    Momentum and got transferred to motion in the molecules of the rubber band (heat), as well as motion of air molecules (sound). If you do the experiment I suggested you'll see why.
  6. Nov 8, 2011 #5
    Thanks for the help Simon
  7. Nov 8, 2011 #6

    Simon Bridge

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    No worries.

    For best effect, repeat the collision experiment with different bumpers.
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