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Is sound wave a transverse wave?

  1. Dec 4, 2013 #1
    i had always belived that sound wave was a longitudinal wave till i come across something saying that its a transverse wave in solid.can anyone explain is it so??
  2. jcsd
  3. Dec 4, 2013 #2


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    In a fluid like air, sound waves are only longitudinal, since fluids don't support shear forces. Solids support both longitudinal and transverse sound waves, and they typically travel at different speeds.
  4. Dec 4, 2013 #3
    if solid support both does that mean that sound is a transverse wave in solids??
  5. Dec 4, 2013 #4


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    There are longitudinal sound waves in solids.

    There are also transverse sound waves in solids.
  6. Dec 4, 2013 #5


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    Sound can be a transverse wave in a solid, but it doesn't have to be transverse. It can be longitudinal instead, like in a gas or liquid.
  7. Dec 4, 2013 #6
    but is sound transverse ,longitudinal or both in solid??
    everyone is telling me that sound can only be longitudinal (my teachers)
  8. Dec 4, 2013 #7
    Inside a solid, sounds is longitudinal. However, at the surface of a solid, sound is transverse. The surface is a like a membrane, its oscillations can only be transverse.
  9. Dec 4, 2013 #8


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    Am desperately trying to picture that

    any further info please ?

  10. Dec 4, 2013 #9
  11. Dec 4, 2013 #10


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    It is almost true by definition, for a common sense definition of "sound". If the surface of the solid doesn't move transversely to the surface, it doesn't transmit any pressure vibrations to the air. (OK, let's ignore the tiny amount of energy that would get into the boundary layer and be dissipated by the air viscosity before it got anywhere else.)

    If course a solid can vibrate with no transverse motion at the surface, for example torsional vibrations of a disc on a shaft, but that type of vibration doesn't generate "sound".
  12. Dec 5, 2013 #11
    you are telling me that it is a longitudinal wave in the solid but transverse wave at the surface.
    do you know any book that can give me further explanation on this topic??
  13. Dec 5, 2013 #12
    I think the answer to the OPs question is no. Sound waves are longitudinal and not transverse. By definition sound waves are related to those types of waves that can be sensed by the ear and the ear drum reacts to longitudinal vibrations.
    A solid may be able to vibrate in different ways but only the longitudinal components of those vibrations can be transferred to any surrounding air as sound waves. It reminds me of the longitudinal and transverse vibrations that can be set up on a stretched string. Both set up longitudinal vibrations (sound waves) in the surrounding air.
  14. Dec 5, 2013 #13
  15. Dec 5, 2013 #14
    There are different modes of vibration in solids but only those that can set up longitudinal waves in the surroundings are related to sound.
  16. Dec 5, 2013 #15
    If you attach a solid body directly to an acoustic sensor, a transverse wave will excite it just the same as a longitudinal wave would.

    If there is an air gap, transverse wave will still excite it. It is quite obvious if you think for a second: most loudspeakers in the world are membranes, and an oscillating membrane is indistinguishable from a surface acoustic wave.
  17. Dec 5, 2013 #16
    The eardrum can be considered as a membrane and this responds most strongly to longitudinal vibrations. It is sound that's being discussed,not vibrations in general.
  18. Dec 5, 2013 #17
    What's your definition of "sound"? And why is your definition relevant for me or anyone else?
  19. Dec 5, 2013 #18
    apparently sound can be longitudinal and transverse wave but air and fluid cannot support transverse wave and sound can be transverse wave in solid
    i need a book to comfirm the hypothesis
  20. Dec 5, 2013 #19
    Vibrations which travel through the air or another medium and are sensed by the ear.
    (Concise Oxford English Dictionary)

    The relevant part of this discussion is that the vibrations "are sensed by the ear" and the ear responds to longitudinal vibrations. Any transverse components eg along the plane of the ear drum will not be effectively passed through.
    I'm not sure at what level of education the op is at but I have a reasonable idea. In the UK system any reference to sound being carried by transverse waves will lose marks.
  21. Dec 5, 2013 #20
    So ultrasound is not sound then?

    I am pretty sure that if a solid bar is made to touch the eardrums, a surface acoustic wave on it will be registered.

    The only reason you can talk about the ear responding to longitudinal vibrations is because ordinarily it senses vibrations in air, which does not support any other. So you are effectively reducing sound to a phenomenon occurring only in air (or perhaps other gases and liquids). Which is at odds with the widely known and recognized concept of sound in solids.
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