Let $\gamma\colon \mathbb{R}\to\mathbb{R}^3$ be a unit-speed curve, and let $t(s),n(s),b(s)$ be the corresponding Frenet frame.
- What is the rotation vector $w$ for the Frenet frame? (better if expressed as a linear combination of $t$, $n$, and $b$)
- Show that $\dot{t} \times \ddot{t} = \kappa^2w$