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Normal force in FBD

  1. Feb 12, 2013 #1
    1. The problem statement, all variables and given/known data

    A box is lifted by a magnet suspended from the ceiling by a rope
    attached to the magnet as illustrated in Fig 3.65. Draw free body
    diagram for the box and for the magnet

    so the picture is basically there is a ceiling , and the rope hanging from the ceiling to the magnet, and the magnet is attached to the box (located below the magnet)

    I am wondering, will there be a normal force in the FBD since the ceiling is the surface? but wouldnt the Fn and Fg be in the same direction? or will it be no Fn because the object and the surface are not in direct contact?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 12, 2013 #2


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    For every force there is an equal in magnitude and opposite in direction reaction force. "Normal force" is a name usually given to a particular kind of reaction force. Using that name in other contexts might be confusing. So, yes, there are reaction forces, but you probably shouldn't call them "normal forces".
  4. Feb 12, 2013 #3

    so do u include it in the FBD?
  5. Feb 12, 2013 #4
    what i am trying to ask it, should this force be included when the object is not in directly contact with the surface
  6. Feb 12, 2013 #5


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    You use all forces in the diagram.
  7. Feb 12, 2013 #6

    Doc Al

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    Staff: Mentor

    If the object is not in contact with the surface, there can be no normal force between them. Since it doesn't exist, you wouldn't include it.
  8. Feb 17, 2013 #7
    thanks for ur reply!
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