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History and Snapshot Graphs

  1. Feb 1, 2017 #1
    1. The problem statement, all variables and given/known data
    Number 6:
    unnamed.jpg For this problem I'm changing the wave speed to 3.0 m/s instead of 1 m/s because that's what our teacher instructed us to do.
    2. Relevant equations
    None that I know of

    3. The attempt at a solution
    I'm having the hardest time making connections between the graphs and more specifically converting one graph to the other. I understand that the snapshot graph represents the displacement of the wave as a function of x and make the analogy of "the experience" a particle will go through. Also I know that the history graph shows what is happening to the medium at the specific point. But when it comes to graphs that are a bit more complex than easier x positions and different velocities I lose track of what's going on.

    With this problem it says it is a history graph at x=2m with the wave moving at 3 m/s. Knowing this I would say that for the snapshot, the 2m will be affected immediately by the wave because of the placement of the leading edge on the history graph.
    I also recognized from my teacher's solution that each second that's hashed on the graph is equivalent to the 3 meters which is understandable, but I really can't connect with what's going on overall. Any help would be greatly appreciated, thank you.

    Here's my teacher's solution: 16-6.jpg
  2. jcsd
  3. Feb 1, 2017 #2


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    2017 Award

    Hello Riceking, :welcome:

    Well, you got most of it!
    From the figure in the book you saw x=2 starts going up at t=0 and is back to 0 at t=4, so the whole snapshot "up from zero" width must be 12 m.
    Similarly: x=2 is at its peak at t=1, so the rising flank of the wave is 3 m wide. With the 1 cm amplitude, that's enough to draw teacher's picture.
    Change from 1 m/s to 3 m/s was probably introduced by teacher becasue 1 m/s is almost too easy (either that, or he doesn't want to see tiny drawings being handed in :smile:)

    My advice: practice.
    What worked very well for me: drawing waves on transparencies and move them sideways over a piece of paper with coordinate lines.
  4. Feb 1, 2017 #3
    Hi BvU thank you for replying. Your explanation makes much more sense than I could understand by myself. Now, after what you said, I infer we use the snapshot graph to dictate what happens to the history graph after moving the position of the snapshot graph back to t=0sec? And for looking at the history graph and drawing the snapshot (like in problem 7), we would move the graph vt = x amount?
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