Mathematics, Vector Calculus, Learning Mathematics, Math.
T is the unit vector in the direction of dR/dt, then dT/ds gives us a normal vector in the same plane as T, because ΔT is in the same plane as T for small values. Coming back to what κ is: dT/ds = |dT/ds| N In the 2D case, |dT/ds| equals |dθ/ds| because the length of the unit vector T is constant,