Definition:Positive Unit Normal
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Definition
Let $S$ be a surface in ordinary $3$-space.
Closed Surface
A positive unit normal to $S$ is a unit normal $\mathbf {\hat n}$ to $S$ at a point $P$ on $S$ such that the terminal point of $\mathbf {\hat n}$ is on the exterior of $S$.
That is, it is constructed outwards from the enclosed region of space.
Unclosed Surface
A positive unit normal to $S$ is a unit normal $\mathbf {\hat n}$ to $S$ whose direction is arbitrarily defined, but usually such that it is generally away from the origin of whatever coordinate system is being used.
Sources
- 1951: B. Hague: An Introduction to Vector Analysis (5th ed.) ... (previous) ... (next): Chapter $\text {II}$: The Products of Vectors: $3$. Line and Surface Integrals