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Homework Help: Measuring gravity

  1. Nov 11, 2009 #1
    1. The problem statement, all variables and given/known data

    My question is. How would the acceleration vs. time graph look if an object was in free fall?

    I am referring here to the picket fence lab.

    3. The attempt at a solution

    My brain tells me, that it would be a horizontal line. But when I think about it, it doesn't really make sense because when the picket fence enters through the photogate the acceleration can't possible be 9.80 m/s^2 , it has to increase over time. So now, I am thinking that the acceleration vs time graph is going to be exactly the same as the velocity vs time graph which is just a increasing line. Is my reasoning correct, or am I not making any sense.

  2. jcsd
  3. Nov 11, 2009 #2


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    Homework Helper

    Your first idea is the correct one in this case.
    In free-fall the acceleration is constant (that is, in free fall over small distances -- when you are talking about distances of several km above the earth surface, you should use the full 1/r2 law).

    Why should the acceleration increase over time? You are confusing it with velocity, which does. However, the increase of the velocity in each time step is constant, which is precisely what a = [/i]g[/i] (9,8... m/s/s) says.
  4. Nov 11, 2009 #3
    Ahh, i see. Yes I didn't think about the small distance at all. Great, thank you.
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