Understanding Velocity in Polar Coordinates

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SUMMARY

The discussion centers on deriving the velocity equation of motion in polar coordinates, specifically addressing the representation of position as \(\vec{R} = R \hat{R}\) rather than \((\theta \hat{\theta} + R \hat{R})\). The key point is that \(\theta \hat{\theta}\) does not represent a displacement since it lacks units of length, making it incompatible for addition with \(R \hat{R}\). This distinction is crucial for understanding the differentiation between linear and angular velocity in polar coordinates.

PREREQUISITES
  • Understanding of polar coordinates and their components
  • Familiarity with vector notation and unit vectors
  • Basic knowledge of calculus, particularly differentiation
  • Concept of linear versus angular velocity
NEXT STEPS
  • Study the derivation of velocity in polar coordinates using calculus
  • Explore the relationship between linear and angular velocity in detail
  • Learn about the applications of polar coordinates in physics and engineering
  • Investigate the implications of unit vectors in different coordinate systems
USEFUL FOR

Students studying physics, particularly those focusing on mechanics and motion in polar coordinates, as well as educators seeking to clarify concepts related to velocity and displacement in non-Cartesian systems.

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Homework Statement



I don't understand why when we derive the velocity equation of motion in polar coordinates we start with position equal to R times R hat and not (theta times theta hat + R times R hat).

Homework Equations



none really..

The Attempt at a Solution



Is there an assumption I'm missing? or is it simply differentiating linear and angular velocity that is messing me up?
 
Last edited:
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It's because your position is given by

[tex]\vec{R} = \begin{pmatrix} x \\ y \end{pmatrix} = \begin{pmatrix} R\cos\theta \\ R\sin\theta \end{pmatrix} = R\begin{pmatrix} \cos\theta \\ \sin\theta \end{pmatrix} = R \hat{R}[/tex]

Also, if you think about it, [tex]\theta \hat{\theta}[/tex] doesn't have units of length, so it's not a displacement and you can't add it to [tex]R\hat{R}[/tex].
 

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