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Combining Equations for Lab report

  1. Sep 19, 2010 #1
    1. The problem statement, all variables and given/known data
    I'm doing a lab report for frequency vs centripetal force and frequency vs radius. I have two tables and I have found the equations for both the graphs. When I combine the equations, should I make another table and how would it look like?


    2. Relevant equations
    f = c0.5
    f = r-1

    3. The attempt at a solution

    I have two tables:

    Table 1: Centripetal Force and Frequency for a constant radius of 60.7 cm and constant rotations of 10

    Centripetal Force (0.1 N) Time Required (0.1 s) Average time (s) Period (for 1 rotation) (s) Frequency (Hz)
    Trial 1 Trial 2 Trial 3
    0.5 9.17 9.47 9.56 9.40 0.940 1.06
    1.0 6.03 6.16 5.89 6.03 0.603 1.66
    1.5 5.68 5.69 5.63 5.67 0.567 1.76
    2.0 4.86 4.90 4.82 4.86 0.486 2.06
    2.5 4.55 4.59 4.53 4.56 0.456 2.19
    3.0 4.35 4.21 4.36 4.31 0.431 2.32

    Table 2: Radius and Frequency for a constant centripetal Force of 1 N and constant rotations of 10
    Radius (0.5 cm) Time Required
    (0.1 s) Average time (s) Period (for 1 rotation) (s) Frequency (Hz)
    Trial 1 Trial 2 Trial 3
    52.2 4.84 4.97 4.66 4.82 0.482 2.07
    55.7 5.56 5.68 5.68 5.64 0.564 1.77
    61.1 6.01 5.96 5.75 5.91 0.591 1.69
    64.9 5.95 6.09 6.01 6.02 0.602 1.66
    69.1 6.20 6.30 6.15 6.22 0.622 1.61
    75.4 6.87 6.77 6.50 6.71 0.671 1.49
     
  2. jcsd
  3. Sep 19, 2010 #2

    Delphi51

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    Homework Helper

    Sounds like an interesting experiment.
    I expect the graph of Fc vs f would be curved. How did you find its equation and what equation did you get?
    Same for the f vs r graph.
    Combining the two equations is kind of tricky; I think a 3rd graph would be quite helpful and the equations you got for the first two would suggest what to put on the axes of the 3rd graph.
     
  4. Sep 19, 2010 #3
    For frequency and centripetal force, I got a graph similar to y = ax^b and for frequency and radius, I got a graph that is similar to y = 1/x

    When I put them together, I got a linear graph y = x
     
  5. Sep 19, 2010 #4

    Delphi51

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    Homework Helper

    Okay, so is that Fc = af^b or f = aFc^b? You need it a little more specifically. Take a wild guess and try Fc = a*f².
    (some people would take a peek at the list of equations for circular motion and notice that Fc = 4π²mrf² so Fc = constant*f² is it!)
    You have to check that by graphing Fc vs f² and it should turn out to be a straight line to within experimental error. Maybe you are supposed to estimate your error in measurement and put an error bar or two on the graph. If you get a straight line, then you know
    Fc is proportional to f².

    You mean f = b/r, right? You could try graphing f vs 1/r and see if you get a straight line.
    I suspect you will have to try f² vs 1/r or f vs 1/r² to get that straight line.

    If all that works out you will know f² is proportional to Fc and also that f² is proportional to 1/r. That suggests f² is proportional to Fc/r, and that you graph Fc vs r*f². A straight line there gives you the formula for how Fc varies with r and f.
     
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