Definition:Curvature/Whewell Form

Definition
Let $C$ be a curve defined by a real function which is twice differentiable.

The curvature $k$ of $C$ at a point $P$ can be expressed in the form of a Whewell equation as:


 * $k = \dfrac {\mathrm d \psi} {\mathrm d s}$

where:
 * $\psi$ is the turning angle of $C$
 * $s$ is the arc length of $C$.

Also see

 * Equivalence of Definitions of Curvature