Definition:Osculating Circle

Definition
Let $I \subseteq \R$ be an open subset of real numbers.

Let $\gamma : I \to \R^2$ be a curve defined by a real function which is twice differentiable.

Let $P$ be a point on $\gamma$.

Let $\kappa_P$ be the curvature of $\gamma$ at $P$.

Suppose $C$ is a circle such that:


 * $P \in C$


 * the tangent to $\gamma$ at $P$ is also a tangent to $C$ at $P$


 * the radius of $C$ at $P$ is equal to $\ds \frac 1 {\kappa_P}$


 * the center of $C$ is on the inner (concave) side of $\gamma$.

Then $C$ is called the osculating circle of $\gamma$ at $P$.

Also see

 * Definition:Radius of Curvature