Curvature Vector

$\begin{displaymath} {\bf K}\equiv {d{\bf T}\over ds}, \end{displaymath}$

where ${\bf T}$ is the Tangent Vector defined by

$\begin{displaymath} {\bf T}\equiv {{d{\bf x}\over ds}\over \left\vert{d{\bf x}\over ds}\right\vert}. \end{displaymath}$