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I Unit normal vector of a surface

  1. Jul 11, 2017 #1
    What is actually the unit normal vector of a surface?
    Is it this?
    Or this one?
    I see that those are opposite in direction. But, I want the correct one, which means that it should point outward.
    So, which one is correct?
  2. jcsd
  3. Jul 11, 2017 #2


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    Both are unit normals. The definition of "inward" and "outward" is dependent on an entire closed region whereas both gradient and cross product are local properties. The meaning of "outward" and can not be defined locally without reference to the larger context.
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