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Nature of waves

  1. Mar 16, 2005 #1
    My question is regarding the nature of waves, and may be a very elementary question. Please bear with me.

    I am curious as to why waves form the way that they do. If for example i were to turn on the speaker in my car, then the resulting wave that is produced is simply energy transfer through air particles. Why does the energy transfer in a wave pattern? Are the air particles actually bouncing off eachother in a pattern that resembles a wave, constantly turning up and down through the medium in which they are traveling? Is there some nature of matter that causes travel through it to propogate in a wave formation? Or does the energy transfer travel in a straight line and the wave is a way of measuring its intensity at any one point?

    Thanks for any help :)

    EDIT: Now that i think about it sound, light, water etc must travel through their mediums in actual wave patterns, otherwise cancellation(like in the 2 slit light experiment) wouldn't happen. Still i'm wondering why waves form the way that they do. Is a wave pattern the path of least resistance for the energy that is being transferred?
    Last edited: Mar 16, 2005
  2. jcsd
  3. Mar 16, 2005 #2

    Andrew Mason

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    To answer this question you have to look at the forces that cause motion to occur, and how those forces vary in time and over space.

    Energy moves in waves where there are restoring forces. If a displacement of matter gives rise to a restoring force, the matter will undergo some form of wave motion.

  4. Mar 16, 2005 #3
    I'm not entirely sure, but your post seems to imply that you beleive that the particles are moving up and down to make a sine wave, like a wave on a rope. This is not how a sound wave is transmitted in air. A sound wave is a compression wave where the air particles transmit the wave by squishing together and spreading apart.
  5. Mar 16, 2005 #4

    "spherical" would be the proper form of a sound wave, not sine. AM is saying that the "duality" of compression/expansion each acts as a restorative or causal force to create the next, larger, wave front.

  6. Mar 16, 2005 #5
    T. Roc,

    I am aware of that the sound wave is not a sine wave. That is what I was clarifying my post, as the OP seemed as though he beleive that a sound wave is like a sine wave.

  7. Mar 16, 2005 #6

    thanks everyone, this helps to clarify it for me :)

    As for electromagnetic radiation, is that different? It seems like there could be no restoring force for that, since its not just a rippling of the medium ...
  8. Mar 17, 2005 #7
    In all waves, the speed goes up with "tension" (think of a stretched string), and goes down with "inertia" (thicker strings = slower speed). The equation is like this:

    [tex]speed = (\frac{tension}{inertia})^1/2[/tex]

    To paraphrase the achievements of J.C. Maxwell in modern notation:

    The restoring force is the electric tension:

    [tex]\frac{1}{\epsilon_0}[/tex] "The permitivity of free space." = 8.85*10^12

    And the inertial element is the magnetic inductance:

    [tex]\mu_0[/tex] "The permeability of free space". = 4*pi*10^-7

    If you relate these in the way common to all waves:

    [tex]speed = (\frac{tension}{inertia})^1/2[/tex]

    Then you calculate a speed of 300,000,000 m/s i.e. the speed of light.

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