Confirming Gauss Theorem with Cylindrical Co-ordinates

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Discussion Overview

The discussion revolves around confirming Gauss's theorem using cylindrical coordinates, exploring the necessary transformations and integration techniques compared to Cartesian coordinates. The scope includes theoretical aspects of vector calculus and the application of coordinate transformations.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant inquires about the process of confirming Gauss's theorem in cylindrical coordinates and whether it parallels the Cartesian approach.
  • Another participant notes that while the idea remains the same, the integration variables, limits, and infinitesimals must be adjusted appropriately when changing coordinate systems.
  • A third participant explains that Gauss's theorem, interpreted as the divergence theorem, is related to the Stokes theorem and can be proven using the Gibbs formulation of vector calculus. They emphasize the importance of changing the volume element according to the Jacobian of the coordinate transformation.
  • This participant further illustrates the necessity of adjusting the volume element when transitioning from Cartesian to cylindrical coordinates, highlighting that the basic unit of volume must be corrected by a factor related to the determinant of the transformation.
  • A later reply asks if there is a specific problem that necessitates applying Gauss's theorem in cylindrical coordinates, suggesting a more concrete discussion could follow.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the transformation of volume elements and the application of Gauss's theorem in cylindrical coordinates. There is no consensus on a specific method or example to apply the theorem.

Contextual Notes

Participants mention the Jacobian and determinants in relation to volume transformations, but there are unresolved details regarding the exact derivation and application of these concepts in the context of Gauss's theorem.

Who May Find This Useful

This discussion may be useful for students and practitioners interested in vector calculus, particularly those exploring coordinate transformations and their implications in theoretical physics and engineering.

SpY]
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How would you go about confirming the Gauss theorem using cylindrical co-ordinates? Could it be just like Cartesian co-ordinates, or what is the transformation?
 
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The idea is the same but your integration variables and limits and infinitesimals have to change appropriately (that is, for example, dxdydz does not just become say, [tex]drd\theta dz[/tex])
 
Gauss's theorem (if you mean the divergence theorem) is a special case of the Stokes theorem, of which there is a simple coordinate-independent proof.
However, you can prove it using the basic Gibbs formulation of vector calculus as well. The gist is the same as the poster states above; the volume element (dxdydz for 3-dimensional Euclidean space with the standard Cartesian coordinate system) changes when you change coordinate systems by the Jacobian of the coordinate transformation. Have you learned the Jacobian, or more generally, derivatives of multivariable vector-valued functions (which your coordinate transformation to cylidrical coordinates is) yet?
In case you have not, or do not see why you need to change the volume element, consider the basic 1 cubic unit of volume in 3-dimensional Euclidean space, which is just 1 x unit by 1 y unit by 1 z unit, analogous to the dxdydz. In analytic terms, the dx dy dz comes from limiting form of a cube with sides delta-x, delta-y and delta-z.
Consider that you want to find the volume of the same cube but you are using cylindrical coordinates. Now your fundamental unit cannot be simply delta-r*delta-theta*delta-z, as that forms an extruded sector when integrated over 1 unit of r, 1 unit of theta, and 1 unit of z, not a unit cube. You must correct this by a factor relating the change in volume between the coordinate systems, which is where the derivative comes in, and more fundamentally the determinant (determinants are fundamentally related to volume).
Your text should have an exact derivation.
 
SpY];2833397 said:
How would you go about confirming the Gauss theorem using cylindrical co-ordinates? Could it be just like Cartesian co-ordinates, or what is the transformation?

Do you have a specific problem where you have to apply this? In that case we could be more concrete...
 

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