Cylindrical coordinates: unit vectors and time derivatives

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SUMMARY

The discussion focuses on the time derivatives of unit vectors in cylindrical coordinates, specifically the rho hat unit vector, denoted as $$\hat{\rho}$$. Participants clarify that the time derivative of $$\hat{\rho}$$ is expressed as $$\dot{\hat{\rho}}=(-\sin{\phi}\hat{x}+\cos{\phi}\hat{y})\dot{\phi}$$, which directly relates to the unit vector $$\hat{\phi}$$. This relationship is established through the transformation of cylindrical coordinates to rectangular coordinates, confirming the correctness of the expressions provided. The insights shared help in understanding the simplification of these derivatives.

PREREQUISITES
  • Cylindrical coordinate system
  • Unit vectors in rectangular coordinates
  • Time derivatives in vector calculus
  • Basic trigonometric identities
NEXT STEPS
  • Study the derivation of unit vectors in cylindrical coordinates
  • Learn about vector calculus and time derivatives
  • Explore the relationship between cylindrical and rectangular coordinates
  • Investigate applications of cylindrical coordinates in physics
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Students and educators in physics and engineering, particularly those studying dynamics and vector calculus, will benefit from this discussion on cylindrical coordinates and their unit vectors.

Mason Smith
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Homework Statement


upload_2019-1-28_14-39-18.png


Homework Equations

The Attempt at a Solution


I have found expressions for the unit vectors for cylindrical coordinates in terms of unit vectors in rectangular coordinates.
upload_2019-1-28_14-40-20.png

I have also found the time derivatives of the unit vectors in cylindrical coordinates. However, I am having trouble seeing how it simplifies. For instance, I do not understand how to arrive at the following for the rho hat unit vector.
upload_2019-1-28_14-46-30.png

Can someone enlighten me, please?
 

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You say you have the time derivatives of the unit vectors. But, if the derivative of ##\hat{\rho}## is not that given, then you must have made a mistake.
 
Mason Smith said:

Homework Statement


View attachment 237940

Homework Equations

The Attempt at a Solution


I have found expressions for the unit vectors for cylindrical coordinates in terms of unit vectors in rectangular coordinates.
View attachment 237941
I have also found the time derivatives of the unit vectors in cylindrical coordinates. However, I am having trouble seeing how it simplifies. For instance, I do not understand how to arrive at the following for the rho hat unit vector.
View attachment 237943
Can someone enlighten me, please?
You have $$\dot{\hat{\rho}}=(-\sin{\phi}\hat{x}+\cos{\phi}\hat{y})\dot{\phi}$$But you already showed that $$\hat{\phi}=(-\sin{\phi}\hat{x}+\cos{\phi}\hat{y})$$
Do you see how it works out now?
 
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Chestermiller said:
You have $$\dot{\hat{\rho}}=(-\sin{\phi}\hat{x}+\cos{\phi}\hat{y})\dot{\phi}$$But you already showed that $$\hat{\phi}=(-\sin{\phi}\hat{x}+\cos{\phi}\hat{y})$$
Do you see how it works out now?
That makes perfect sense. Thank you so much for the insight, Chestermiller! :smile:
 

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