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Oscillation Period

  1. Feb 9, 2015 #1
    1. The problem statement, all variables and given/known data

    Assume that the potential is symmetric with respect to zero and the system has amplitude ##a##, show that the period is given by : ##T=\sqrt{8m}\int^a_0\frac{dx}{\sqrt{V(a)-V(x)}}.##


    2. Relevant equations

    ##E = \frac12 m(\frac{dx}{dt})^2+V(x)##


    3. The attempt at a solution

    For a particle, I know that at ##t=0## if we release it from rest at position ##x=a## we then have ##\frac{dx}{dt}=0## at ##t=0## and thus ##E=V(a)##. So when the particle reaches the origin for the first time it has gone through one quarter of a period of the oscillator. Thus, I have to integrate with respect to t from ##0## to ##\frac{T}{4}## and rearrange the equation ##E## for ##\frac{dx}{dt}##. But from here I am not sure how to set it up properly to get ##T=\sqrt{8m}\int^a_0\frac{dx}{\sqrt{V(a)-V(x)}}.##
     
  2. jcsd
  3. Feb 9, 2015 #2
    Hi. Indeed you already have everything to set up your integral:
    If you substitute your value of E in Hamilton's equation, can you separate the variables (functions of x on one side, functions of t on the other)?
     
  4. Feb 9, 2015 #3
    I have ##V(a) -V(x) = \frac12m(\frac{dx}{dt}2) \implies 2\sqrt{V(a)-V(x)} = m\frac{dx}{dt} \implies \implies \sqrt{\frac{2}{m}}dt = \frac{dx}{\sqrt{V(a)-V(x)}}## but I am confused on how they to get ##T##.
     
  5. Feb 9, 2015 #4
    What about integrating both sides? You know the limits of the integrals (for t and x) from your first post, so what do you get?
     
  6. Feb 9, 2015 #5
    When I am integrate I am not sure how they got the ##\sqrt{8m}##.
     
  7. Feb 9, 2015 #6
    What do you get when you integrate dt from 0 to T/4?
     
  8. Feb 9, 2015 #7
    We will get ##T/4## if we integrate dt from 0 to T/4.
     
  9. Feb 9, 2015 #8
    Ok, then what is (T/4)⋅(2/m)1/2?
    This is just algebra...
     
  10. Feb 9, 2015 #9
    Oh wow.. how dumb am I. Thank you very much!
     
  11. Feb 20, 2017 #10
    Can you show step by step procedure? I am confused
     
  12. Feb 20, 2017 #11

    haruspex

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    The thread is a year old. Quite possibly neither participant still uses PF. If you have been given the same homework problem, please follow forum rules by posting your own attempt. A new thread might be best.
     
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