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Homework Help: SHM Pendulum length/gravity question

  1. Sep 12, 2011 #1
    T= 2pie Square root of 2L/3g

    I got a couple of questions.

    1) why is it 2L/3g?
    2) would my straight line graph be T^2 vs L? ( so gradient is T^2/l?)
    3) after i get my gradient do i compare it to the gravity 9.81?
    4) is the equation gonna be time^2=XXL or s^2=xxm ? do i use the unit or the quantity?

    thanks so much for your help. I'm doing the experiment tomorrow and need to know ASAP. cheers
  2. jcsd
  3. Sep 12, 2011 #2


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    Welcome to Physics Forums.
    (1a) I'm assuming that your using a "rod pendulum", in which case: http://hyperphysics.phy-astr.gsu.edu/hbase/penrod.html#c1

    (1b) And for a general physical pendulum: http://hyperphysics.phy-astr.gsu.edu/hbase/pendp.html#c1

    (2) That depends on what you're measuring (dependent variable) and what you're varying (independent variable). If this is a standard "measuring g with a pendulum" experiment, I would think you would be plotting T2 vs. L, yes. Although, I'm not sure how you're going to vary the length of the rod easily.

    (3) The general equation of a line [through the origin] is [itex]y=mx[/itex], where [itex]m[/itex] is the gradient. So, if you're plotting T2 vs. L your gradient would be [itex]8\pi^2/3g[/itex].

    I would have thought all of this would have been explained by your instructor.
    Last edited: Sep 12, 2011
  4. Sep 12, 2011 #3
    dam this is a hard experiment. Yes i am doing a rod experiment.

    2) I'm guessing we going to get different length of rods provided. So i assume it's T^2 vs L.
    ALso. For working out the gradient. I think it's L/ T^2 =X and then re arrange the fomula. G ( gravity)= (4(pi^2)2X) / 3 is it correct?

    3) oh im just wondering for the equation do i use the quantity or the unit?

    also i was reading the page u add. for measuring the length. It's from the pivot to the center of the rod?? why is that? why not the whole length?

    Well this is actually a internal for my school tomorrow. But the teacher allows us to see the test paper before hand. Since my school is having a mock exams this week i only go to school for exams. Didn't have time to go school and ask. I doubt my teacher would help me. He's probably gonna tell me go home and think about it myself.

    very appreciated for your time sir. I'm so grateful someone can help me out at this time. thank you. :)
    Last edited: Sep 12, 2011
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