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Homework Help: Surface normal directions

  1. Sep 2, 2010 #1
    How do I find "surface normal direction" for a plane on a point with coordinates specified?
    Last edited: Sep 2, 2010
  2. jcsd
  3. Sep 2, 2010 #2
    Do you have a plane equation or do you only have the coordinates of a point? Please be more specific.
  4. Sep 2, 2010 #3
    i need to find normal directions for r^2=9 and x+y+z^2=1 at the point (2,-2,1)
  5. Sep 2, 2010 #4


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    Homework Helper
    Gold Member

    First, neither of those surfaces are planes. The first is a spherical shell, and the second is a paraboloid.

    Second, straight from wikipedia:

    I'd be shocked if this wasn't in your notes or textbook, and I strongly suggest you review the section of your text that covers this.

    Anyways, just like wikipedia implies, to find a surface normal at a point, define [itex]F[/itex], take the gradient (in the appropriate coordinate system) and plug in the point.
    Last edited by a moderator: May 4, 2017
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