Vector Rotation About Arbitrary Axis

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    Axis Rotation Vector
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Discussion Overview

The discussion centers on the mathematical representation of vector rotation about an arbitrary axis, specifically focusing on the transformation of a vector \( v_{\perp} \) as described in a referenced document. Participants explore the expression \( T(v_{\perp}) = \cos(\theta) v_{\perp} + \sin(\theta) w \) and seek clarification on its derivation and implications.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant requests clarification on how the transformation \( T(v_{\perp}) \) is derived as \( \cos(\theta) v_{\perp} + \sin(\theta) w \).
  • Another participant expresses confusion about the graphical representation, noting that the figure appears as an ellipse rather than a circle.
  • A participant questions the rationale behind expressing the vector as a sum of \( \cos(\theta)v_{\perp} \) and \( \sin(\theta)w \), suggesting it resembles vector addition.
  • Further clarification is sought on whether the question pertains to the correctness of the expression or its utility.
  • One participant explains that the transformation involves rotating vectors in a plane perpendicular to the rotation axis, where \( v_{\perp} \) and \( w \) are perpendicular unit vectors, thus justifying the relation.
  • Several participants express gratitude for the explanations, indicating a resolution of their confusion.

Areas of Agreement / Disagreement

There appears to be some agreement on the understanding of vector addition and transformations, but initial confusion exists regarding the graphical representation and the derivation of the expression. The discussion does not reach a consensus on the clarity of the initial explanation.

Contextual Notes

Participants express varying levels of understanding regarding vector addition and transformations, indicating potential gaps in foundational knowledge or assumptions about the graphical representation.

MD Aminuzzaman
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I am new to this forum. I was reading this document :
http://math.kennesaw.edu/~plaval/math4490/rotgen.pdf

Here the author says that from this figure
http://i.stack.imgur.com/KBw9l.png

that we can express $v_{\perp}$ like this :
$$T (v_{\perp}) = \cos(\theta) v_{\perp} + \sin(\theta) w$$

I don't understand this part. Can anybody explain how $$T(v_{\perp}) $$ is $$\cos(\theta) v_{\perp} + \sin(\theta) w$$?
 
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Any Help?
 
Isn't this obvious from the figure? I see no problem at all.

Although what should be a circle looks like an ellipse in the figure I see on my computer. Could be something wrong with the graphics the author used. Anyway, if you also see an ellipse, think of it as a circle!
 
Why we are experessing the Vector as addition of cos(θ)v⊥ and sin(θ)w ? Is it the result of 2 vector addition like Vab = Va + Vb?
 
Is your question why it is correct to do this, or what is the use of doing this?
 
why it is correct to do this ?
 
Don't you know how to add vectors geometrically, with the parallellgram law?

Here we are studying a linear tranformation which rotates every vector in the plane perpendicular to the rotation axis by the angle ##\theta## about that axis. Then ##v_\perp## is mapped to ##T(v_\perp)## in the figure. And ##v_\perp## and ##w## are perpendicular unit vectors in this plane, so we obtain the relation stated.
 
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Thanks now i understood. Sorry sometimes i am dumb and gets confused with simpler things.
 
MD Aminuzzaman said:
Thanks now i understood. Sorry sometimes i am dumb and gets confused with simpler things.
No problem, you're very welcome! We all get confused sometimes.
 

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