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B Why are electromagnetic forces body/volume forces?

  1. Oct 30, 2016 #1
    Hi,

    I dont really get what the point of volume forces is, if electromagnetism is a volume force. Its obviously no surface force, but in my opinion the definition says that its no volume force as well. The link below describes volume forces as "a force acting on all particles (volume elements) of a given body and proportional to the mass of the particles. Gravitationalforce is an example of a volume force.".
    But electromagnetic force doesnt affect neutrons. They also affect some particles more than others: electrons and protons have different mass and especially different charge.
    Gravity is different. Every bit of mass is affected equally?!
    Every source I found says its a body force so my thoughts must be wrong. Does anyone see where my mistake is?

    http://encyclopedia2.thefreedictionary.com/Volume+Force
     
  2. jcsd
  3. Oct 30, 2016 #2

    mfb

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    Staff: Mentor

    That does not matter. Its effects are in the whole volume, not limited to the surface. An interaction that would only affect electrons would still be called "volume force" if it would act on all electrons in the material.

    With the same argument as you used for the charge, you could say "protons are heavier, they are affected more by gravity".
     
  4. Oct 31, 2016 #3
    Ok, thank you.. So I think the definitions I read are a bit misleading.
    Protons should fall with 9,81m/s² and electrons, too. So they actually get affected the same... Or am I mistaken? Are the protons of a body on earth pulled down more? That doesnt really make sense to me...
     
  5. Oct 31, 2016 #4

    mfb

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    Depends on what you call "the same" - same force or same acceleration?
    For protons the force is larger. The acceleration is the same for both of course.
     
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