# Use this form of radius vector

1. Sep 1, 2004

### xz5x

(vector) F = r^4 r(vector)
Find me rotor of F

Rotor of vector F must be 0, but I don't know how . You can't use this form of radius vector: xi+yj+zk (i, j, k are vectors), just leave r.
Thank you!!!

Last edited: Sep 1, 2004
2. Sep 1, 2004

3. Sep 2, 2004

### xz5x

Thank you..but I didn't find the wright answer there

4. Sep 2, 2004

### Feynman

What do you need by this question ?
let be must claire

5. Sep 2, 2004

### xz5x

This is what I need:
nabla x F
F = r^4 r (bold are vectors)..(r is radius vector)
The result of this is 0, but I don't know how...

6. Sep 2, 2004

### Tide

Well, if you can't or won't work with spherical coordinates then do it by brute force using the definition of curl. Just remember that the unit vector $\hat r$ is not a constant with respect to position!

7. Sep 3, 2004

### xz5x

Tide, I really don't know what to do with spherical coordinates. Maybe you can show me.
But, I found another way..Here it is:

nabla x r^4r =
= r^4rotr - r x grad r^4
= 0 - r x dr^4/dr r/r
= - r x dr^4/dr r/r
= - dr^4/dr 1/r rxr
= 0

btw. bold are vectors; curl=rot; nablaxnablaf=0; rot r=0; rxr=0

Can somebody tell me is this correct???