# Polar Kinematics

1. Oct 31, 2006

### sherlockjones

If we have a position vector $$\vec{r} = x\vec{i} + y\vec{j}$$ why is the polar form of the equation $$r = r\vec{r}$$? Don't we need two parameters to define a postition? And $$r$$ is the magnitude of $$\vec{r}$$?

Thanks

2. Oct 31, 2006

### geoffjb

The two parameters are $r$ and $\theta$.

http://mathworld.wolfram.com/PolarCoordinates.html