# Time-evolution of a vector

1. Dec 27, 2009

### Niles

Hi all

Say I have a time-dependent vector v. Lets say that I find

$$\frac{d}{dt}\br{v} = \br{q}\times v \perp \br{v},$$

where q is a vector. Am I allowed to conclude that the vector v rotates around q as time evolves?

2. Dec 27, 2009

### Niles

Oh, I realized it now. It becomes clear when you make a drawing that the vector v really does rotate (precess) around q as time evolves.

Thanks.