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Does the acceleration of a free falling object ever change?

  1. Sep 15, 2015 #1
    Have to make a table of measurements, height-time-velocity-acceleration, taken from a free falling object and my professor asked for the acceleration of each trial which is leaving me very confused because I thought g = 9.8ms2 is constant. So I'm going to have to write a bunch of 9.8s or is there I'm overlooking.
     
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  3. Sep 15, 2015 #2

    Doc Al

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    Presumably you are being asked to measure the acceleration. You're unlikely to get the same answer in each trial or measure exactly 9.8 m/s^2. Errors happen!
     
  4. Sep 15, 2015 #3

    Nidum

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    An object falling in air accelerates at something less than 1g due to air resistance .

    For a heavy stone it doesn't make much difference but a light plastic football will accelerate at much less than 1g .

    Also air resistance tends to increase with velocity so acceleration rate might decrease as object moves faster .
     
  5. Sep 15, 2015 #4

    Ray Vickson

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    Do you think that a feather, or a light styrofoam packing peanut will fall with the same acceleration as a lead fishing lure? Even if you measure the falls of a fishing lure several times, from different heights, for example, do you really thing you will get exactly 9.8 m/sec^2 each time?
     
  6. Sep 15, 2015 #5
    Sorry, I should of mentioned air resistance is negligible for this particular lab or the actual acceleration is the main focus by rather that we become familiar with the applications and equations orbiting this subject.

    I know a lot of programming so it just kind puts me off and leaves me a bit confused as to why to add something that is redundant....well, not sure if redudant is the right word but I can't really think of a synonym on how vexing this simple detail is. It just seemed to me that he was implying that g was changing despite it being a constant.
     
  7. Sep 15, 2015 #6

    Doc Al

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    Are you measuring the acceleration or simply assuming it?
     
  8. Sep 15, 2015 #7

    Nidum

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    In VI physics many years ago we did this experiment and eventually got results which were consistent within a few % . Average value of course was always less than 1g because air was certainly present .
     
  9. Sep 15, 2015 #8
    The only actual things being measured is the time via sensors connected to a computer and the height. We're computing velocity manually just with the latter two measurements, height and time.
     
  10. Sep 15, 2015 #9

    Doc Al

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    And then using those values to compute the acceleration. Right?
     
  11. Sep 15, 2015 #10

    Ray Vickson

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    Making several independent measurements and taking the average (and, perhaps, performing a statistical error-analysis) is a cornerstone of an experimental science. Nobody has ever managed to make perfect measurements that are 100% accurate 100% of the time. Learning how to reduce experimental errors if possible, and to deal with them in any case, is basic to performing lab experiments in physics and other sciences.

    Anyway: the best way of understanding how and why is to try it for yourself. That way you will see that it is not a useless, "busy-work" type of project.
     
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