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Difference between people 'doing the wave', and a transverse wave?

  1. Jul 9, 2006 #1
    I don't have my textbook any more, but I remember a question in there about this. I think it asked for the difference between people in a stadium 'doing the wave', and a real transverse wave. I couldn't really think of why they're different. I mean they're pretty similar, right? The people 'doing the wave' stand up and sit down, simulating the effects of molecules moving up and down in a transverse wave. What's the difference though?

    Could someone help soon please? Thanks in advance.
     
  2. jcsd
  3. Jul 9, 2006 #2
    Well, I know that in a real wave, all of the particles are connected. In a stadium, if a group of people doesn't stand up, the wave can keep going. In a physical transverse wave, not only is it impossible for a section of the wave to just stop (Unless a force is stopping it), the wave couldn't continue on without those particles. That leads into the fact that no energy is transfered either.

    That's just my guess, though. I can't think of any other reason.
     
  4. Jul 9, 2006 #3
    This isn't true, a sound wave is a perfect example, sound is a longitudinal wave that is transmitted by the particles in air, if there is a place where the density of these particles is smaller than another point then not all of the wave can be transmitted without some loss of quality of the sound, also note that none of these particles are connected to any of the others.
     
  5. Jul 9, 2006 #4

    nrqed

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    But the question is specifically about transverse waves. It is true that of there is no restoring transverse force between adjacent particles, there can't be any transverse wave. For example, there is no transverse wave inside a liquid (I am not talking about at the surface but within th ebulk of the liquid)
     
  6. Jul 9, 2006 #5
    That makes sense, sorry I guess I just didn't notice the transverse wave part, thanks for correcting me.
     
  7. Jul 10, 2006 #6
    So you're saying that because the 'doing the wave' can continue without a few people, the two are different? I think I see that, but can anyone think of anything else?
     
  8. Jul 10, 2006 #7

    J77

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  9. Jul 10, 2006 #8

    nrqed

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    I think an important point is that a transverse wave of people can go ta any speed. If people decide to move up and down faster, the wave will propagate faster. The speed is up to what people decide to do.
    In a real medium, the speed is fixed by the property of the medium and of the restoring force so for a fixed medium, one cannot change the speed (for example for a transverse wave on a string, the speed is [itex] {\sqrt{ {T \over \mu} }} [/itex].

    Just a thought..

    Patrick
     
  10. Jul 10, 2006 #9
    Oh, I see, that makes sense too. Anyone have any other ideas? Keep in mind it's only gr.11, so I don't don't think anything too complicated would be involved, the examples so far have been pretty good.
     
  11. Jul 10, 2006 #10
    A big difference is that the people's positions do not oscillate simple harmonically . For eg, the person gets up for only a brief instant as the wave crosses him, and then sits down for some period until the wave comes back to him after traversing the stadium once. I guess in the real world sense, it is more of a pulse than a wave.There is no actual source of "disturbance" either .
    Of course, if the stadium were really small and the spectators really quick, you could simulate a wave, but noone would call that a Mexican wave .
     
    Last edited: Jul 10, 2006
  12. Jul 10, 2006 #11
    Mexican wave? What's that?
     
  13. Jul 10, 2006 #12
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