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Wave: amplitude, frequency, wavelength

  1. Jan 8, 2013 #1
    1. The problem statement, all variables and given/known data
    Original question: A boy flicked a string harder, describe the changes of the waveform and the speed of the wave.


    2. Relevant equations
    V = f x λ
    Frequency is how many completed oscillation per second.
    Wavelength is distance between two adjacent points of the same phase on a wave.


    3. The attempt at a solution
    My answer: Amplitude will increase, and speed remain unchanged. Flicked harder, more energy received, amplitude bigger. Speed depend on medium, so unchanged.

    My confusion:
    1. The displacement of pendulum is amplitude, how to find wavelength from there?
    Let said From A to B to C to B to A. Is the wavelength is the distance move by the pendulum along the path?


    2. If the amplitude turn bigger but the speed remain, it should take more time to go up and down, so wavelength become shorter?

    3. By assume statement 2 is correct, according to the formula, frequency should be higher. Am I right


    Very confused.
    ahchew1413
     
  2. jcsd
  3. Jan 8, 2013 #2

    jedishrfu

    Staff: Mentor

    A key feature of a given pendulum is that the period is always the same no matter what the starting conditions are.

    This is why pedulums play a big role in early science.

    http://en.wikipedia.org/wiki/Pendulum
     
  4. Jan 9, 2013 #3
    I still can't understand how to find wavelength from the pendulum. Can you kindly explain a bit.

    thanks,
    ahchew
     
  5. Jan 9, 2013 #4

    haruspex

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    More information needed. Is this string as a pendulum, and the boy makes the pendulum swing wider? Or is this a travelling transverse wave being sent down a string by a flick? Or is it a stretched string with a standing transverse wave?
     
  6. Jan 9, 2013 #5
    hi haruspex:

    The original question regarding the wave:
    It is a travelling transverse wave being sent down a string by a flick. The boy create a transverse wave the a rope, then, he flicked harder to see the changes.

    Why the flick does not change the frequency and wavelength? Was it because the medium (the rope) does not change, as a result, speed does not change. So, frequency and wavelength does not change also?



    Other question that not related to original question.
    How do we find the wavelength from a pendulum?

    thanks,
    ahchew
     
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