let a(t) be a regular curve which lies on the unit sphere in R^3
a(t) . a(t) = 1 for all t
i want to show that the geodesic torsion Tg(t) vanishes for such a curve.
i can use the fact that a(t) can be interpreted as a unit normal N(t) to the surface along he curve.
can anyone help me with this question? thanks