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Homework Help: 3 Questions about Waves

  1. Dec 11, 2009 #1
    Hi there,

    I have some questions which i hope forummers can contribute or give feedback. I have given thoughts to these questions as well, and i have written them in brackets for fellow forummers to critique.

    1. If wave transfer energy but not matter, why a floating bottle in the middle of the sea will drift gradually to shore?

    (My take on this question is that the wind plays a supporting factor. In additon, when waves break on shore, debris floating on the previously waves will get transported to shore. Wave breaking, after all, is the basis of how wind surfing works.)

    2. Besides longitudinal and transverse waves, are there different types of waves?

    (My take on this question is no. Other than a perpendicular, parallel or even circular axis of vibration of particles, of which we will then be talking about water waves, there cant be other axis of vibrations.)

    3. What makes a good sound absorber?

    (I understand the key concept is one of elasticity. Elasticity is not one of "stretchiness" , but rather the ability of a material that has changed shape when struck, to resume its initial shape when the striking force is removed. But still, it doesnt help to explain why rubber is a good sound absorber.I mean, rubber does go back to its initial shape right?! )

    Thanks. And hope to hear your valuable comments soon.
     
  2. jcsd
  3. Dec 11, 2009 #2

    diazona

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    Homework Helper

    1. The matter of the stuff that's waving - in this case, ocean water - doesn't move (very much), but that doesn't mean it can't push other things along. Even without wind, a wave could move a bottle along the surface of the ocean.

    2. You could have a wave that's not associated with anything moving, and that wouldn't be either longitudinal or transverse. For example, a wave of magnetic moment alignments in some ferromagnetic material (although I'm not really sure whether that would be possible in reality). Or you could simulate a numerical wave in a computer. But... when particle motion is involved, I believe all waves are either longitudinal or transverse, or some combination of those, since there isn't any other direction for the particle to move. (This also applies to electromagnetic and gravity waves, even though no medium of particles is involved in them)

    3. Basically, it's the ability of the material to dissipate energy from pressure waves at the frequencies which are typical for sound. Generally speaking, soft things (rubber, cloth) are better dissipators than hard things. It takes a lot of energy to squash or dent or distort a hard object, and sound waves just don't have that much energy. So if the energy of the sound wave isn't enough to distort (break) the object, it has to bounce back. By contrast, something soft like rubber is easily distorted and it has no problem absorbing energy from sound.
     
  4. Dec 11, 2009 #3
    Thanks Diazona, for this quick and wonderful reply!
     
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