1. Sep 11, 2007

captain

what do radius vectors of particles really mean and how can they be at a different angle with velocity v.

2. Sep 11, 2007

bsmith2000

The radius vector $$\vec{r}$$ is the vector from some origin to the position of the particle at some time $$t$$. Typically, $$\vec{r}(t)$$ is the trajectory, so to speak of the particle, so the derivative with respect to time is the velocity: $$v_t = \frac{d\vec{r}}{dt}$$. Because the position is constantly changing, the velocity as well as the angle changes with respect to the origin.