Mathematics, Vector Calculus, Learning Mathematics, Math.
is “normal” to both T and N. (Why we use the word “normal” for “orthogonal” I don’t know). dB/ds is how B changes with time and since B is a unit vector (because T and N are unit vectors), dB/ds is just the change in direction of B. And |dB/ds| is the magnitude of this change: dB/ds = d(T x N)/ds =