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Waves - Matter is transported or not?

  1. May 24, 2012 #1
    Waves -- Matter is transported or not?

    We are talking about waves in class. It stated in the reading that matter is not transported during a wave. However, water in the middle of the ocean is not proof that waves do not move matter, because even if waves do move matter, gravity would pull the water to the lowest possible point, evening the surface and returning water to the middle of the ocean.
    Am I right or wrong?
     
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  3. May 24, 2012 #2

    mathman

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    Re: Waves -- Matter is transported or not?

    What is the context of the discussion - electromagnetic (such as light or radio) or water or sound?

    Water waves - things move around, such as waves on a beach or tsunamis.
     
  4. May 24, 2012 #3

    sophiecentaur

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    Re: Waves -- Matter is transported or not?

    Water waves are a difficult type of wave to study as a start because they are a combination of transverse and longitudinal waves. I would be easier to discuss sound or waves on strings. However. . . . .
    As you say, in the middle of the ocean, it is clear that nothing actually has a net movement in any direction - a floating ball just goes up and down and forwards and backwards in a circular motion. But there appears to be a 'loophole' in that statement about no transport of matter when the water nears the land. However . . .
    When the water gets shallow, the speed of the waves gets less and the crests tend to fall over (break) because they overtake the troughs. The wave loses its shape and it is true that sometimes a beach ball can be pushed in towards the beach. BUT the water itself only ever gets so far up the beach (apart from the tide, which tends to cloud the issue in the sea). It's thrown forward but drains back - so there is still no net movement of the water - even though there is a lot of forward /backwards movement. So that basic initial statement about waves is still true.
     
  5. May 24, 2012 #4
    Re: Waves -- Matter is transported or not?

    Meh, teachers and textbook writers get too overzealous when they try to convey these science "facts" that they don't say that they are only true in a certain limiting case. Water waves certainly can move matter... it's just that most of the wave motion in the ocean is up-down.
     
  6. May 24, 2012 #5

    sophiecentaur

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    Re: Waves -- Matter is transported or not?

    Look at the theory of surface waves. The motion is in a vertical circle and not up and down.
    It is true that you can launch a wave by 'pushing forward' and there is a flow of water 'away' but this disperses rapidly (DC is restored) and there is no forward flow. If there were then the logic tells us that there would be a build up of water at one side (or the other, or both sides, possibly) of the sea. Is there evidence of this? What goes on in the 'near field' is not included in this, of course because we would be dealing with the interaction of a wave with a structure of some sort, not just a wave.

    But the statement in textbooks is not actually about "moving matter", as in 'pushing things'. It refers to movement of the actual medium. As I wrote earlier, water (surface) waves are not the best examples for an elementary discussion because the wave is more complex than most other wave motions.
     
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