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Homework Help: Simple Harmonic Motion formula

  1. Nov 22, 2005 #1
    Hi. I've got a problem here about Simple Harmonic Motion. There is "formula" in our physics coursebook for the distance travelled by an object : s=4AN=4At/T
    s-distance travelled
    N-number of cycles

    Is it true for every case or just for N=1, 2 , 3 ?
    I guess it is true for N=1, 2 , 3 but not sure, can u explain it please?

    P.S Sorry for mistakes during translation
  2. jcsd
  3. Nov 22, 2005 #2


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    Homework Helper

    The ultimate challenge to you here is to derive the formula!

    What is the distance travelled by an object in 1 complete cycle or period (i.e. t = T)? Describe this in terms of the oscillation amplitude.

    Then go for two, and three?
  4. Nov 22, 2005 #3
    In SHM the amplitude is constant, so yes it is true for all N and indeed any fractional value of N (i.e. a half cycle covers a distance of 2A), assuming it is actual distance travelled rather than displacement being measured and s = 0 and N = 0 at t = 0.

    As for why it is true, consider an oscillator at equilibrium at t = 0. It will travel as far as it can from equilbrium (its amplitude, so s = A), then back down to equilibrium (A again, so total s = 2A), then its amplitude in the other direction (total s = 3A), then back to equilibrium (total s = 4A) making a cycle (N = 1). In SHM, each subsequent cycle will be the same as the 1st, so the total distance travelled will be 4A times the number of cycles.

    The period T is the time taken to go through one cycle, so the total time taken t divided by T will tell you how many cycles have occurred, hence N = t/T.

    Why did you think N = 1, 2, 3 would be special?
  5. Nov 22, 2005 #4
    In SHM "v" and "a" are not constant so i thought it is not true to find distance for example in t=T/6 T/5 and so on
  6. Nov 23, 2005 #5
    Do you know any site or other source hat i could get more information about this?
  7. Nov 23, 2005 #6
    Actually, yes you're right. The right-hand side is only true for values of t that are multiples of T/4. However, this will always be the case for integer values of N, or even multiples of N/4, assuming N = 0 and s = 0 when t = 0. Sorry, I was focusing more on s = 4AN.
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