2
$\begingroup$

I have two vectors in spherical coordinates, both originating at the origin and both with the same magnitude equal to one. One is vertical: {1,0,0} and the other undefined: {Ms,Mt,Mp}. The other one can be anywhere depending on an energy equation. I need to know the angle between them. So I take the dot product:

$ (1,0,0) \cdot (Ms,Mt,Mp) = Ms+0+0=Ms= \left| 1\right| \left| \text{Ms}\right| \cos (\omega )$

Therefore $~~~~\cos (\omega ) = 1 ~~~~~~~~$ and $ ~~~~ \omega = ArcCos[1]$

But, it doesn't make sense that no matter the direction of the vector the angle is constant.

Where did I go wrong?

$\endgroup$
  • $\begingroup$ In spherical coordinates, how do you get $(1,0,0) \cdot (Ms,Mt,Mp) = Ms+0+0$? The pairwise multiplication of coordinates is a formula that works in Cartesian coordinates, but the two coordinate systems are very different. Also, if both vectors have magnitude $1$ then $Ms=1$, doesn't it? $\endgroup$ – David K Feb 14 '16 at 0:26
  • $\begingroup$ Ms does equal 1. $\endgroup$ – Joseph Feb 14 '16 at 0:27
  • $\begingroup$ I'm looking at dot products and not seeing the adjustment for spherical coordinates. $\endgroup$ – Joseph Feb 14 '16 at 0:36
  • $\begingroup$ There's no "adjustment". It just doesn't work that way at all. $\endgroup$ – David K Feb 14 '16 at 1:08
  • $\begingroup$ So my only recourse is to convert to cartesian coordinates, take the dot product, and convert back to spherical coordinates? The integrating Jacobian or the like will not suffice in a vector dot product? $\endgroup$ – Joseph Feb 14 '16 at 18:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.