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Effect of motion on energy

  1. May 17, 2010 #1
    we know that physical objects are affected by motion, their energy increases as they are accelerated. what about pure energy ? say i have a box with some potential energy stored in it (like a coiled spring or a battery etc). when i accelerate this setup, there will be change in the mass of the materials, but will the potential energy stored in the spring also change ?
     
  2. jcsd
  3. May 17, 2010 #2

    phyzguy

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    Yes, it will. One way to see this is to study the energy associated with the electromagnetic field and see how it varies as the velocity changes. This energy will increase by the same factor gamma = 1/sqrt(1-v^2/c^2) that mechanical mass increases. In fact, it was by studying the behavior of electromagnetism that Einstein and others derived special relativity.
     
  4. May 17, 2010 #3
    oh i was on the impression that motion wont have any effect on light or EMR. consider this setup where we have any apparatus where pulses of light are produced. when we move the apparatus close to speed of light, the velocity of the light emitted from aparatus, will still remain the same. also, i believe there wont be any change in its frequency or amplitude, which means the motion has no effect on its energy content. pls correct me if im wrong here....
    actually i was thinking about time and im a firm believer that time is a man made concept. In reality time doesnt exist. any physical entity can be detected or measured ? what about time ? (clocks don't measure time)
    my explanation for non variance of speed of light is that, motion has no effect of EMR and hence time doesnt apply to EMR. time applies only to physical objects (rather, we humans can apply time only to matter)
     
  5. May 17, 2010 #4

    phyzguy

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    If two observers with different relative motion view light (electromagnetic radiation), it's true they will both see the light moving at the same speed. But the frequency and hence the energy content of the radiation will be different as viewed by the two observers. Because the two observers view time and space differently, one will see the light to have a longer wavelength (lambda) and lower frequency(nu) than the other, while the product (lambda*nu = c) will be the same.
     
  6. May 17, 2010 #5
    thanks for the clarification !
     
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