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Why does an electric charge stop moving?

  1. Mar 18, 2014 #1
    If an electric charge is placed into an electric field of a charge that has been around for a while, it will start to move until equilibrium is reached, or until it's field has propagated out as far as the other charge. Note that the charges are connected by some non-conductive material.

    Why/how does the charge stop moving?

    Thanks.
     
    Last edited: Mar 18, 2014
  2. jcsd
  3. Mar 18, 2014 #2

    Drakkith

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    If the charges are opposite, they will both accelerate until they collide with each other and form an atom, which would be "equilibrium". If the charges are alike, then both will accelerate away from each other forever, with the magnitude of the acceleration dropping as the distance between the two charges increases, but never reaching zero.
     
  4. Mar 18, 2014 #3
    The charges are connected. Forgot to put that originally.
     
  5. Mar 18, 2014 #4

    Drakkith

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    We talking about point charges, IE electrons and protons, or about macroscopic objects that happen to be charged?
     
  6. Mar 18, 2014 #5
    Two wires, two point charges, two things that are charged. This is for a final, and I'm having difficulty remember all the details of what was discussed, which is why I'm having trouble remembering why. I think the teacher did it with two wires connected to a non conductive material. After the first wire's field had propagated, the second wire was turned on. (No, this isn't in the book)
     
  7. Mar 18, 2014 #6

    Drakkith

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    Unfortunately the details are important. Performing this experiment on two electrically charged wires in a laboratory is much different than two point charges in free space. If you'd like to, feel free to construct a specific scenario and ask about it.
     
  8. Mar 18, 2014 #7
    It's all conceptual, and thus in space. All I need is why the apparatus stops moving once the second field has propagated. I'm sure the reason doesn't differ much depending on how the apparatus is designed in the conceptual world.
     
  9. Mar 18, 2014 #8

    Drakkith

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    The 2nd field never stops propagating since the EM force has an infinite range while changes in the field propagate at a finite speed.
     
  10. Mar 18, 2014 #9
    But the apparatus, which would begin to move in the time it takes for the second to propagate, would stop moving. I need to know how/why. I realize once it passes the other charged object it still keeps going.
     
  11. Mar 18, 2014 #10

    Vanadium 50

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    You're asking us to explain "how/why" before you have described "what". We can't do that - like Drakkith says, the details are important.
     
  12. Mar 18, 2014 #11

    Drakkith

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    The only way for the apparatus to stop moving, as far as I can tell, would be for it to lose energy by emitting EM radiation. Otherwise it would keep spinning or oscillating forever. It's hard to say since we don't have a specific setup.
     
  13. Mar 19, 2014 #12

    sophiecentaur

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    I don't understand why you think it would stop moving. The only thing to stop the object moving (in the absence of other forces, would be if the charges were opposite and they bump into each other.
    As usual, a diagram would help a lot.
     
  14. Mar 19, 2014 #13

    Vanadium 50

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    Let's wait for the OP to describe the system. Completely describe the system. Guessing won't help him.
     
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