Unit Vectors and Spherical Coordinates

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SUMMARY

The discussion focuses on the derivation of the unit vector \(\hat{r}\) in spherical coordinates, specifically addressing the formula \(\hat{r} = \frac{\frac{d\mathbf{r}}{dr}}{|\frac{d\mathbf{r}}{dr}|}\). Participants clarify that this approach utilizes the derivatives of the position vector \(\mathbf{r}\) with respect to the spherical coordinates \(r\), \(\theta\), and \(\phi\). The conversation emphasizes the importance of understanding the geometric interpretation of these derivatives, as they relate to the surfaces formed by holding each coordinate constant. The use of graphical methods to visualize the surfaces and derive the unit vectors is also highlighted.

PREREQUISITES
  • Understanding of spherical coordinates and their representation.
  • Familiarity with vector calculus, particularly derivatives and unit vectors.
  • Knowledge of geometric interpretations of coordinate systems.
  • Basic proficiency in using mathematical notation and expressions.
NEXT STEPS
  • Study the derivation of unit vectors in spherical coordinates.
  • Learn about the geometric interpretation of partial derivatives in multivariable calculus.
  • Explore the application of cross products in vector calculus to find orthogonal vectors.
  • Investigate graphical methods for visualizing surfaces in three-dimensional space.
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Students and educators in mathematics, physics, and engineering, particularly those studying vector calculus and spherical coordinates.

jesuslovesu
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Homework Statement


\mathbf{r} = rsin(\theta)cos(\phi) \hat x + rsin(\theta)sin(\phi) \hat x + r cos(\theta) \hat z
I am kind of following the description of the process given at http://mathworld.wolfram.com/SphericalCoordinates.html

I want to find \hat r and I understand everything except:
Why is \hat r = \frac{\frac{d\mathbf{r}}{dr} }{|\frac{d\mathbf{r}}{dr}|} (why the derivatives)?

Normally if I were going to find the unit vector I would just say the unit vector u hat = u/|u|
 
Last edited:
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I'm not exactly sure what you're asking, but i have a feeling you want to find the base vectors in spherical. To do so, it might be easier to do so graphically. To find the vectors you need to look at the surfaces that are created when you hold each of r, theta, and phi constant, individually. So, when you hold r constant your surfaces are spheres. to find a unit vector that is normal to the surface, you just use the fact that x = rsin(phi)cos(theta), y = rsin(phi)sin(theta), z = r cos(phi), and then divide the vector by its length. When you hold theta constant you get a sheet that hangs from the z axis. when you hold phi constant you get cones. THe easiest way to find all of them is to find 2 and then do a cross product (in the appropriate order so your sign is correct) on them to find the third. hope this helps some
 
jesuslovesu said:

Homework Statement


\mathbf{r} = rsin(\theta)cos(\phi) \hat x + rsin(\theta)sin(\phi) \hat x + r cos(\theta) \hat z
I am kind of following the description of the process given at http://mathworld.wolfram.com/SphericalCoordinates.html

I want to find \hat r and I understand everything except:
Why is \hat r = \frac{\frac{d\mathbf{r}}{dr} }{|\frac{d\mathbf{r}}{dr}|} (why the derivatives)?

Normally if I were going to find the unit vector I would just say the unit vector u hat = u/|u|

They ARE using u/|u|. But the u's they are applying that to are the vectors pointing in the coordinate directions, the partials dR/dr, dR/dtheta and dR/dphi (where R is the vector r).
 

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