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Waves & Matter

  1. Mar 17, 2006 #1
    Thats a quote from one of my physics texts, but it seems to me to contradict what ive been tought about enrergy and matter thus far, which isnt much i must add.

    If wave motion can be defined as energy transfer without matter transfer, then doesnt that violate the famous equation?

    If so, how would you define a wave?
  2. jcsd
  3. Mar 17, 2006 #2

    Doc Al

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    Staff: Mentor

    I think what they are trying to say is this: A mechanical wave transfers energy through a medium, but the medium itself does not get transferred from one point to another. Like sound energy travels through the air, but the air itself doesn't travel. (It just vibrates back and forth.) Or a ripple of a water wave traveling outward without the water itself moving outward.

    (Don't worry about relativistic effects, if that's what you are thinking.)
  4. Mar 17, 2006 #3
    How is energy transfered in a wave?

    I understand the role of a medium for a mechanical wave, and that there is an absence of a medium for an electromagnetic wave moving through free space, or more to the point, the medium is ( though not a true medium ) the oscillations in the elctronic and magnetic fields.

    I apreciate your reply, but i am worrying about relativistic effects :) maybe you can help clear my confusion a little.

    Another thing that bothers me, is, hypothetically speaking, assuming the parallel postulate to be flase, what effect would such a condition have on the EM wave model?

    thx :)
  5. Mar 18, 2006 #4


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    What equation?

    Consider a microphone: sound waves cause it to vibrate, generating electricity, yet the air isn't moving from one place to another.

    Consider an electric guitar - the guitar string doesn't move away from the guitar, yet it generates electricity in the pickup.

    Consider an old-style reciprocating steam engine: the piston moves back and forth (net displacement: zero), yet it produces energy by spinning a shaft.
  6. Mar 18, 2006 #5
    E=mc^2 was the equation i was reffering to.

    If you transfer energy, then dont you also transfer some mass?
  7. Mar 18, 2006 #6


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    Yes, actually, you do. It's the reason the components of a nuclear bomb have less mass after the bomb goes off than before it goes off.
  8. Mar 18, 2006 #7

    i don't think you need to transfer mass. for example, fire a laser beam. you transfer energy but no mass (considering photons to be massless).
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