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What is sound?

  1. May 3, 2013 #1
    I am looking for a definition of sound. Does it have anything to do with what is perceived by the ear, and therefore restricted to certain frequencies? Is it even a perception or is it simply a longitudinal wave? I can find lots of physics material about sound, but I can't find a definition.
  2. jcsd
  3. May 3, 2013 #2
  4. May 3, 2013 #3
  5. May 3, 2013 #4
    Thats the case for lots of words. Definitions are often context dependent.

    From the context of the post and forum I would say that definition number one is what you want.
  6. May 3, 2013 #5


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    Well, there are several different words which are spelled 'sound'.

    1. A sound is one type of a body of water.
    2. Sound is that natural phenomenon which is perceived by the ear.
    3. etc., etc.

    When using a dictionary, it helps to winnow out which definition is of interest by knowing the part of speech, the context (as MP stated), etc. In English, there is no guarantee that a word will always have a single definition.
  7. May 3, 2013 #6
    To be more specific, how would a physicist define sound?
  8. May 3, 2013 #7
    The same way as everybody else. "Sound" doesn't have a specific technical meaning in physics (unlike "work" or "force").
  9. May 3, 2013 #8


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    I disagree with #1 because the propagation of vibrations should qualify as sound whether or not it is audible to a witness. Noise, on the other hand, should require an audience because the term implies something that causes irritation.
  10. May 3, 2013 #9
    Should? Definitions are arbitrary, none of them "should" be anything.
  11. May 3, 2013 #10


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    But they should be objective.

    If an experiment in acoustics "doesn't work" because the experimenter is deaf, there's something wrong somewhere!
  12. May 3, 2013 #11
    Objective? I'm not sure what that means with respect to definitions. I would agree that they should be useful and perhaps practical.

    As for your situation, I would say there is something wrong - using a deaf person.

    Otherwise, I have no objection to Danger's definition. I wouldn't be surprised if it was defined like that somewhere.
  13. May 3, 2013 #12
    I took your suggestion and googled "define"

    From Google

    State or describe exactly the nature, scope, or meaning of.


    a. To state the precise meaning of (a word or sense of a word, for example).

    Macmillan Dictionary http://www.macmillandictionary.com/us/dictionary/american/define

    to describe clearly and exactly what something is

    Based on the definition of "define", I was hoping someone could provide the precise meaning of the word "sound". I'm thinking a physicists would probably have the most precise definition.
  14. May 3, 2013 #13


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    The main reason that I consider vibrations to be sound with or without an observer is that we use the speed of sound in a medium as the fastest rate at which a signal can be transmitted through it mechanically. For instance, we have received several questions about "faster than light" information from people who figured that you can push on the end of a stick here on Earth, who's other end is on Mars, and have that push be instantaneously transmitted. The proper response is that the movement can't propagate faster than the speed of sound in wood. Ignoring the logistical problems regarding orbital mechanics, the lack of a person on Mars doesn't negate the fact that a shift of mass occurs only after a significant delay. That push is "sound" because it involves the transfer of energy along a chain of atoms.
    As I was asked in high-school, by someone who I can't remember: If Helen Keller falls over in the forest, does anyone hear her?

    edit: Kjamha, I just spotted your last post. Bear in mind that most definitions are not consistent among differing cliques. You will not get the same ones from different bodies of expertise.
    Last edited: May 3, 2013
  15. May 3, 2013 #14
    They dont, probably because there isn't much need to define sound precisely. Many things do get very precise definitions in physics, but sound is not one of them.
  16. May 3, 2013 #15
    Danger's post #13 is a great description. Understand sound by what it is mechanically: a bunch of atoms slamming into their buddies.
  17. May 4, 2013 #16


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    Crack me up.
    ( And that one went over how many persons heads....... )
  18. May 4, 2013 #17


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    Apparently one less than I expected... :biggrin:
  19. May 4, 2013 #18


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    I would say sound is simply pressure waves moving through atoms.
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