Velocity in plane polar coordinates

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SUMMARY

The discussion centers on the relationship between the magnitude of the change in the radial unit vector, Δer, and the change in angle, Δθ, in plane polar coordinates. It is established that the arc length spanned by Δθ is represented as δ = |er|Δθ, where |er| is the unit magnitude of the radial vector. Due to the small size of Δer, it is concluded that Δer is approximately equal to δ, leading to the assertion that Δer ≈ Δθ. This geometric interpretation clarifies the connection between angular displacement and radial displacement in polar coordinates.

PREREQUISITES
  • Understanding of plane polar coordinates
  • Basic geometry principles related to arc length
  • Familiarity with unit vectors
  • Knowledge of angular displacement concepts
NEXT STEPS
  • Study the derivation of arc length in polar coordinates
  • Explore the properties of unit vectors in vector calculus
  • Learn about the applications of polar coordinates in physics
  • Investigate the relationship between angular velocity and linear velocity
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Students and professionals in mathematics, physics, and engineering who are working with polar coordinates and seeking to deepen their understanding of velocity concepts in this coordinate system.

marcom
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Hi,
I have a problem with the following explanation of velocity in plane polar coordinates.
30sik39.jpg

I don't understand why the magnitude of Δer is approximately equal to Δθ.

Thanks
 
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You know from basic geometry that the arc of circumference spanned by ##\Delta \theta## is going to be ##\delta=|\hat{e}_r|\Delta\theta##. However, even if ##\Delta e_r## is actually straight, it is very very small and so it will be close in magnitude to the arc of length. Also since ##\hat{e}_r## has unit magnitude, you find ##\Delta e_r\simeq\delta=\Delta\theta##.
 
Thanks!
 

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