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Homework Help: Phase difference of 2 points in a same graph

  1. Jun 7, 2014 #1
    1. The problem statement, all variables and given/known data

    since point P is ahead of point O, why the displacement , y , of P shouldnt be Asin(wt + 2pi/(x)) ?

    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

  2. jcsd
  3. Jun 7, 2014 #2
    Be careful, the graph is against x not t.
  4. Jun 8, 2014 #3
    sorry, stil dont unseratand . can you explain further?
  5. Jun 8, 2014 #4


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    Staff: Mentor

    Think of the figure as a snapshot photo of an ocean swell.

    Imagine O and P are corks floating on the ocean, and they rise and fall as the wave gently passes. At the moment captured in the photo, cork O is falling and crossing the zero line. How far must the wave move along (sliding along to the right) before cork P in turn finds itself falling through the zero line?

    So P is lagging O by ....?
  6. Jun 8, 2014 #5
    so are you assuming falling downward dispalcement is positive? floating upward dispalcement is negative since you said P is lagging behind by O. how do we know which direction is positive and which is negative (falling downward or floating upward) ?
    Last edited: Jun 8, 2014
  7. Jun 8, 2014 #6


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    Staff: Mentor

    Defintely not assuming anything. I described how you could see things were you to imagine this as an ocean swell; I used an analogy.

    You are told that movement is described as A.sin(ωt), so that's where you might choose/assume '+' direction if it's not explicitly indicated.

    Any and every motion of O will be emulated at a time Δt later by a point which lags O by that amount of time, regardless of what that instantaneous motion of the sinusoid may be. Whatever O is doing will be copied by P a short time later.
    Last edited: Jun 8, 2014
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