A silly question about unit tangent and unit normal

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    Normal Tangent Unit
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Discussion Overview

The discussion revolves around the concepts of unit tangent and unit normal vectors in the context of vector calculus. Participants explore methods for determining the unit normal vector, particularly in relation to the unit tangent vector, and whether there are quicker methods than those typically presented in textbooks.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about finding the unit normal vector and questions if there is a quicker method than what is typically shown in textbooks.
  • Another participant asks about the dot product of the unit tangent and unit normal vectors.
  • A response indicates that the dot product of the unit tangent and unit normal vectors is zero, but notes that this alone does not provide enough information to determine the unit normal vector due to having two unknowns.
  • It is suggested that the length of the unit normal vector provides another equation to solve for the unknowns.
  • A method is proposed where one can visualize the tangent vector and rotate it 90 degrees to find the normal vector, leading to the conclusion that if the tangent vector is (a, b), the normal vector must be (-b, a).
  • A later reply acknowledges the proposed method and expresses gratitude for the clarification.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the quickest method for finding the unit normal vector, as there are multiple approaches discussed, including both algebraic and geometric methods.

Contextual Notes

The discussion includes assumptions about the properties of unit vectors and the relationships between them, which may not be explicitly stated. There are also unresolved aspects regarding the application of the proposed methods.

Who May Find This Useful

This discussion may be useful for students or individuals studying vector calculus, particularly those interested in the geometric interpretation of tangent and normal vectors.

athrun200
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I know how to obtain the unit tangent, it is very easy. But for the case of unit normal, I am confused.

Usually we need to know [itex]\vec{T'}(t)[/itex] and |[itex]\vec{T'}(t)[/itex]|
in order the find [itex]\vec{N}(t)[/itex].

However are there any quicker method to do it? Since I saw the textbook do it without step, it seems there is a quicker method.
 

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What's the dot product of T and N?
 
SteamKing said:
What's the dot product of T and N?
0

But it is not enough.
Since [itex]\vec{N}[/itex]=a[itex]\hat{i}[/itex]+b[itex]\hat{j}[/itex]
There are 2 unknows, a and b.

Dot product yields only one equation, this is not enough to get [itex]\vec{N}[/itex]
 
You said N was a unit normal. The length of N gives you another equation for a and b.

The "easy" way to get the answer is to draw a picture of the tangent vector, and rotate it through 90 degrees to get the normal vector. It should then be clear than if the tangent vector is (a, b), the normal vector must be (-b, a).
 
AlephZero said:
You said N was a unit normal. The length of N gives you another equation for a and b.

The "easy" way to get the answer is to draw a picture of the tangent vector, and rotate it through 90 degrees to get the normal vector. It should then be clear than if the tangent vector is (a, b), the normal vector must be (-b, a).

Oh! Thanks a lot!
 

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