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Centripital Force Lab

  1. Oct 27, 2006 #1
    Hey i just had a question on a centripital force lab I did in school today. We had what was essentiall a hollow tube with a string through it, at one end was a hanging mass and on the other was a rubber stopper. The radius was kept constant by a clip marking the radius so it could not move higher or lower. The stopper was spun around with increacing masses hanging. We then had to calculate the V_T which i had no problem with. The Actual centripital force was the hanging mass converted into weight. When calculating the theoretical centripital force we used the formula
    mv^2
    r

    Then to get percent error actual-theoretical/actual x 100.

    My question is i have percent error for a few in the hundreds, is there a reason for this such as the radius kept changing, or counting the revolutions could have been wrong considering how fast it was.

    P.S im sorry if i didnt make this clear if i didnt ill clear it up to the best of my ability.


    Thanks for taking the time to look,

    -Steve
     
  2. jcsd
  3. Oct 27, 2006 #2

    Chi Meson

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    Hmm, sounds familiar.

    A few common errors in this lab:

    Which mass did you multiply by g to get the "actual" Fc ?

    Which mass did you use in the mv^2/r formula?

    Did you square the speed?
     
  4. Oct 27, 2006 #3
    I multiplied for the first trial by .055kg and i used the same mass for the remainder of the calculations. And yes, i did remeber to square the speed, i did it separately to make sure i did not forget that step. Heres the calculations I had.

    hanging mass: .055kg
    time for n rev.= 5.12s
    n of rev.=10

    n2pir/T= 102pi(.37m)/5.12s = 4.5 m/s

    actual F_c 9.8(.055)= .54N

    theoretical F_c= mv^2/r=.055(4.5)^2/.37=3.0N

    %difference
    .54-3.0/.54= 4.6 x 100= 460% error ????

    I must have done something wrong
     
  5. Oct 27, 2006 #4

    Chi Meson

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    Yes, you did something wrong. The "m" in the "theoretical" Fc is not the hanging mass, but the mass of the stopper. What was it, 0.012 kg?
     
  6. Oct 28, 2006 #5
    Wow. Yes, it was close to that at .0102kg.

    Thank you.

    -Steve
     
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