The product of the two "principal" forms of this quantity is equal to its (*) Gaussian form.
One version of this value is given as the quotient of the determinants of the two fundamental forms. The derivative of the unit tangent vector is equal to this quantity times the unit normal vector. By the Theorema Egregium, this value is invariant under local isometry. The product of the two "principal" forms of this quantity is equal to its (*) Gaussian form. This quantity and torsion are the two scalars present in the Frenet-Serret formulas. This value for a circle is given as one over its radius. For 10 points, name this mathematical quantity intuitively defined as how unstraight a line is.
One version of this value is given as the quotient of the determinants of the two fundamental forms.
curvature