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Wave speed as a function of compression?

  1. Apr 9, 2012 #1
    Dear physics forum, I am doing an experiment on the vibrational behavior of beams and a question has come up that I can't answer. How does compression affect wave speed?

    Brief overview of the experiment:

    studying the change in vibrational behavior of a beam that is gradually tapered toward a point (equilateral triangle). Basically I have four beams:
    Beam 1: uniform rectangle
    Beam 2: tapering begins
    Beam 3: more tapering
    Beam 4: beam comes to a point at one end.

    The beams are clamped at one end, with the other end open. If you take the ground to be the 'x-axis', then the length of the beam is in the 'x-axis', the width in the 'z-axis', and the height in the 'y-axis'. Aka the beam, which is quite flexible (synthetic trim board), does not sag due to gravity.
    Their is a sin-wave generator located 100mm from the clamped end. I've found that even when i hang the beam, or stand it up (clamp closest to ground), the node placement does not change. What i have found, is that the wavelength decreases the farther i get from the clamped end, aka the wave speed is decreasing.
    basically i've got compression on the bottom and tension on the top of the beam. I know v=sqrt(T/u), but does anyone have any insight into wave speed as a function of compression?

    any insight is welcome, thanks
     
  2. jcsd
  3. Apr 11, 2012 #2
    Is the beam made out off two parts of which one is under tension and the other under compression? Or what is being compressed by what?


    Roman.
     
  4. Apr 11, 2012 #3
    If you are talking about sound waves, the speed of sound depends on the bulk modulus. See https://en.wikipedia.org/wiki/Speed_of_sound
    I suppose if most materials are compressed, the bulk modulus will increase, so the sound speed should increase.
     
  5. Apr 11, 2012 #4
    If you are talking about sound waves, the speed of sound depends on the bulk modulus. See https://en.wikipedia.org/wiki/Speed_of_sound
    I suppose if most materials are compressed, the bulk modulus will increase, so the sound speed should increase.
     
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