1. Nov 14, 2011

### seshikanth

As we know grad F (F surface) is in normal direction. But we also have (grad F(r)) x r = F'(r) (r) x r = 0
this implies grad F is in direction of r i.e., radial direction. Radial and normal directions need not be same. Can any öne clarify THE DIRECTION OF GRAD VECTOR?

Last edited: Nov 14, 2011
2. Nov 15, 2011

### seshikanth

Gentle reminder

3. Nov 15, 2011

### HallsofIvy

In your second formula, you refer to "F(r)" so you are assuming that F depends only on r and so is spherically symmetric. The first formula does not assume that .

4. Nov 16, 2011

### seshikanth

Got it! Thanks!