Talk:Surface normal

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[edit] What does it all mean!?

"A surface normal holds the three dimensional direction a surface faces in a 3 component vector representation."

Can't this be stated a little more clearly? I don't understand what is meant.

S.

Probably. It could also benefit from a simple graphic. I know what it means—I'll try to get around to it. —Frecklefoot 18:52, 28 Aug 2003 (UTC)

Okay, I edited the definition and added a graphic. I hope it is clearer now. If not, mention it here and I'll try to clrify it even more. :-) —Frecklefoot 20:34, 28 Aug 2003 (UTC)

I took off the stub notice, it looks pretty well fleshed out now. (if someone more mathematical disagrees, they can put it back. --ObscureAuthor 20:37, 28 Aug 2003 (UTC)

[edit] Outward-pointing normal

I reverted recent changes to this article as they were not carefully written.

• The picture with an inward pointing normal is not good looking, and a bit confusing.

• The concepts of inward and outward pointing normals do not make sense unless one defines what is the "inside" and what is the "outside" of a surface, so I guess it does not make sense to all surfaces.

• The wording "Normals do not penetrate the surface." does not make sense.

As such, the new changes had a point, but were poorly written to the point of being incorrect. Comments? Oleg Alexandrov (talk) 22:34, 20 May 2006 (UTC)

Theory says a smooth surface in 3D has a tangent plane at each point. Displacements between points in that plane are perpendicular to exactly two opposite directions. A normal vector is a non-zero vector pointing in one of the two directions; often, but not always, a normal vector has unit length. If a vector is an equivalence class of parallel, equal-length, and consistently directed displacements, which is how a mathematician might view the matter, then it makes no sense to speak of vectors penetrating anything. If a surface is not closed or not orientable (like a Möbius strip), then we cannot speak of inside or outside. We may draw pictures of vectors as physical arrows in space, but we should not confuse the picture with reality. --KSmrq^T 01:16, 22 May 2006 (UTC)

But how does this relate to an ellipsoidal surface? For instance, look at Figure 1.4 on the top of pg.8, here (PDF): Would that nearly horizontal ring connecting points A and B be the curvature of the "normal section"? If it is, what would the "ring" that connects the two points, cutting through the center of the ellipsoid (i.e., a "great circle"), , be the curvature of?: The "central section" or "subtended section"? Orthodromic section? ~Kaimbridge~13:14, 22 May 2006 (UTC)

[edit] Surface Normal Outward Normal Left and Right hand rules

Hi KSmrq Re: Article Surface Normal

The word "outward" was edited out of the caption of the image with the advice to stay away from that adjective. However S. P. Timoshenko, recognized as the father of Engineering Elasticity, in his book Theory of Elasticity uses the symbol "N" to represent "outward normal to the surface of a body" The images in the book showing normals are exactly identical to the image in the article.

If an outward normal is to be recognized, shouldn't an inward normal be also recognized? The inward normal vector represents a pressure

If one of the two normals is determined by the Right-hand rule, isn't the other normal, in the opposite direction, uniquely determined by the Left-hand rule?

If you do not mind would you kindly respond Subhash 01:04, 17 June 2006 (UTC)

Retrieved from "http://en.wikipedia.org/wiki/User:Subhash15/Trial2"

I am happy to respond.

The title of the book refers to the "surface of a body", which a mathematician might paraphrase as the boundary of a solid in 3D. Such a solid has a well-defined inside and outside, so the terms "outward" and "inward" can have meaning for the surface. However, mathematicians deal with many surfaces that are not boundaries of solids, including some for which it is demonstrably impossible to distinguish or define "outward" and "inward". A mundane example is a triangle in space; which side is which? But the triangle still has two sides, which is not always so. For example, the famous Möbius strip, a cylindrical strip with a half twist, has only one side. An engineer would never encounter such a surface as the boundary of a solid, but mathematicians encounter them often. Elsewhere in engineering the mathematician's view is needed, so please don't be mislead by one special case.

I am responding here because I do not monitor the talk page of the surface normal article, but in future you should conduct such discussions where all interested parties can see, learn, and participate, on the article talk page. --KSmrq^T 04:28, 17 June 2006 (UTC)

(the section up to here copied from User talk:KSmrq by Oleg Alexandrov (talk) at 07:58, 17 June 2006 (UTC))

I totally agree with KSmrq here. Oleg Alexandrov (talk) 07:58, 17 June 2006 (UTC)