Nonconservative gradients (not an oxymoron)

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Discussion Overview

The discussion revolves around the concept of nonconservative vector fields and their relationship to gradients of surfaces. Participants explore the implications of curl and gradient in a specific vector field, questioning the nature of these mathematical constructs and their interpretations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents a vector field defined as fx,fy = -y,x and claims that its curl is 2, suggesting that this indicates a counterclockwise rotation and a spiral surface.
  • Another participant questions the clarity of the initial explanation, specifically how the curl of a vector can be a number and how a gradient of a three-variable equation can be represented as a two-dimensional vector.
  • A later reply reiterates the initial claims but seeks clarification on the assertion that the surfaces are spirals, emphasizing the need for a clearer understanding of the relationship between the vector field and potential surfaces.
  • It is noted that the curl of the vector field is constant and non-zero, leading to the conclusion that the vector field cannot be a gradient of a scalar field, but surfaces orthogonal to the vector field do exist.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the vector field and its implications. There is no consensus on whether a nonconservative field can be considered a gradient of a surface, as some argue against this while others maintain their position.

Contextual Notes

There are unresolved questions regarding the definitions and interpretations of curl and gradient in this context, as well as the assumptions made about the nature of the surfaces related to the vector field.

okkvlt
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fx,fy=-y,x
curl(fx,fy)=2

its counterclockwise so the gradient is pointing ccw.
the gradient is the direction of max increase, so
then the surface z=f[x,y] whose gradient is -y,x is a spiral/screw whose z position goes up forever as x and y are traced out counterclockwise

so, a nonconservative field IS a gradient of a surface.
why was i lied to?
 
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I think you're going to need to write this out clearer. How can the curl of a vector be a number? How can the gradient of a three variable equation be a two dimensional vector?
 
Last edited:
okkvlt said:
fx,fy=-y,x
curl(fx,fy)=2

its counterclockwise so the gradient is pointing ccw.
the gradient is the direction of max increase, so
then the surface z=f[x,y] whose gradient is -y,x is a spiral/screw whose z position goes up forever as x and y are traced out counterclockwise

so, a nonconservative field IS a gradient of a surface.
why was i lied to?

Hello there! Okay, let's take it step by step and yes, please do be a little clearer so we can understand exactly what you're saying. I think what you're saying is that you're trying to find the surface whose gradient at each point is (-y,x,0)? How did you make these out to be spirals?


So let's see, you've got the vector field:

[tex]\vec{V} = (-y, x, 0)[/tex]

Ye? And you've calculated its curl, which is:

[tex]Curl \vec{V} = (0,0,2)[/tex]

so the field is 'rotating' counterclockwise viewed from above (the positive z axis). The curl of your vector field is constant in all of space, and non-zero. Because it is non-zero means that your vector field [tex]\vec{V} = (-y, x, 0)[/tex] cannot be a gradient, in other words, there is no scalar field whose gradient is [tex]\vec{V}[/tex]. That is, there are no surfaces whose gradient at each point is (-y, x, 0). But! this does not mean that there are no surfaces which are orthogonal at each point to [tex]\vec{V}[/tex]. In fact, in your case, these surfaces DO exist, because the vector field [tex]\vec{V}[/tex] is normal to its curl.
 
Just to help visualize, here is the curl of your vector field V, as viewed from above:

http://img31.imageshack.us/img31/4605/curl.gif
 
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