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Kinetic Energy vs Gravitational Potential Energy Experiment

  1. May 12, 2010 #1
    Here is a summary, written by me, of an experiment I carried out:

    4501730599_90d5dee072_o.png

    Is the method correct (if you recognise the experiment)? Are the results and conclusion correct (do any of the figures/calculations seem significantly wrong)? Is there anything more I could say for the conclusion? Any ideas would be much appreciated!
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
    Last edited: May 13, 2010
  2. jcsd
  3. May 12, 2010 #2

    diazona

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    For one thing, it's an inclined plane (not plain).
     
  4. May 12, 2010 #3
    Anything else related to the Physics itself?
     
  5. May 12, 2010 #4

    diazona

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    I can't quite visualize the experiment, so I don't think I can make any meaningful comment on the physics in it (which is why I just pointed out the misspelling). I mean, your formulas are correct and the numbers look reasonable.

    Actually... on a second look, one thing that did catch my eye is that the difference between kinetic energy and potential energy (or your % error, if you prefer to think of it that way) gets larger the more mass you use. To me, that could indicate that maybe the potential energy lost is actually not equal to the kinetic energy gained. I mean, of course I know that it is supposed to be equal, and so do you I presume, but your data don't quite back up that conclusion. What you seem to have found is a relationship more like
    [tex]mgh = \frac{1}{2}mv^2 - \alpha (m - m_0)[/tex]
    and if it were me, I'd be suspicious enough to look into what the origin of that [itex]\alpha[/itex] term might have been.
     
  6. May 13, 2010 #5
    Could it be the times are wrong? What would the ideal results be?
     
  7. May 13, 2010 #6

    diazona

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    Hey, you're the one who did the experiment :wink: How would I know if the times are wrong?

    And think about it, you know what the ideal result should be... keep in mind, though, that in experimental science just because your data doesn't back up the ideal/expected result, it doesn't necessarily mean you screwed up. There are sources of error that you can't control that make your data vary a bit from what you expect, but it's your responsibility to recognize, and ideally account for, any variations you find.
     
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