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  • Rice

    Make sure your speakers aren't turned way up!
    Coach Pat Summitt - Folding at Home

  • #2
    That is pretty darn cool!

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    • #3
      Fascinating! So what was I seeing?

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      • #4
        I believe you were seeing the rice form patterns based how the metal plate vibrated to various frequencies. As the plate vibrated the vibrating areas were cleared of rice which migrated to the areas of the plate that were not vibrating.
        Jack

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        • #5
          That's a pretty good one. :applause:

          The metal plate vibrates in response to the sound waves (probably coming from a speaker directly below it) in the air. The waves actually propagate through the metal, which is interesting in it's own right, because the pressure wave of sound in air (a longitudinal wave) is transformed into a vibration in the metal, side to side (a transverse wave). The cool patterns are formed, like Jack said, based on which parts of the metal are shaking and which parts are holding still. The specific pattern is the result of the interaction of the waves as they reflect (echo) back and forth through the material. It's strange to think that a wave travelling through a piece of metal is reflected by ("bounces off") air at the edge of the metal, but it does, in a way. (Well, the air doesn't have anything to do with it; the behavior would be the same in a vacuum.)

          What's particularly interesting to me about this is that it works as a conceptual model for room resonances and the bass frequency interactions people work so hard to eliminate in their home theaters. The places where rice accumulates is the nulls in response, while the other areas (specifically, near the center of the open areas) are relative peaks in response. It illustrates the way bass response can vary quite dramatically within a room when the location of the low frequency source allows these patterns to develop. This would be an extreme example, as no one would intentionally locate their sub in the precise center of their room - now you've seen why you shouldn't (only in two dimensions instead of three).

          Here's a couple links to animations, graphics, and resources I used when I taught physics to high schoolers:
          http://paws.kettering.edu/~drussell/...t/reflect.html (this professor's site is really good for waves - he has a lot of cool animations on a number of pages)
          http://hyperphysics.phy-astr.gsu.edu...standw.html#c4 (hyperphysics is written and maintained by a professor at Georgia State who taught me about physics - the whole site is a great reference for virtually any physics topic.)
          http://paws.kettering.edu/~drussell/...s/driving.html (This is actually Dr Russell's description of why you shouldn't put subwoofers in certain places.)

          http://paws.kettering.edu/~drussell/...flect/soft.gif
          http://www.kettering.edu/~drussell/D...2/monopole.gif

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