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Sound waves in a 1-molecule thick liquid

  1. Aug 16, 2007 #1
    Imagine a 1-molecule thick layer of liquid, evenly dispersed across a perfectly flat surface. This surface is (for this thought experiment) impenetrable and sound does not pass through it; it is unable to resonate or vibrate.

    If we apply sound waves or some other frequency/wave generation to the liquid, what will happen? Will it experience peaks and valleys? If so, what will be "under" the peaks?

    What if this 1-molecule thick liquid is sandwiched between two of these impenetrable plates (that is, two plates 1 liquid-molecule's width apart, with this liquid in between them)? Can waves pass through the liquid? If so, how would they form and what would they look like? What if we have no liquid, but air in this space between the plates? Remember that the plates themselves do not resonate.

  2. jcsd
  3. Aug 16, 2007 #2


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    Sound waves are compression waves and would smply move molecules closer or further apart. Assuming the source of the waves was strong enough to overcome the intermolecular forces they would travel normally.

    When sound moves through air in a room it doesn't lift up in front of the speaker. I think you are taking the analogy of a wave on a string too literally.
  4. Aug 16, 2007 #3


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    As mgb_phys points out, sound waves are not transverse waves; they are compression/rarefaction waves.

    Take a slinky, one end in each hand. To send a transverse wave through it, you'd wave one hand perpendicular to the length of the slinky. To send a compression wave through it, you'd push one hand in the direction of the slinky's long axis (squishing it).

    Your petrie dish of liquid would transmit sound waves just fine.
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