LESSON 3.2 · 2:46 · CHAPTER 3 · PATHS ON CURVED SURFACES

A fibre's angular momentum

Clairaut's relation is a conservation law. A bead coasting on a surface of revolution with no friction and no gravity keeps constant speed and constant angular momentum about the axis, so R sin α is constant: it follows a geodesic and turns at the same radius as a geodesic fibre. Friction lets R sin α drift; that drift is steering.