These are central examples in Riemannian geometry of manifolds with nonpositive sectional curvature. This results in a curved boundary with its curvature towards itself. These are the normal curvature, geodesic curvature and geodesic torsion. Its surface has zero Gaussian curvature everywhere. All these curves are roulettes with a circle rolled along another curve of uniform curvature. The curvature is the reciprocal of radius of curvature. The Gaussian curvature coincides with the sectional curvature of the surface. In most cases including the cases of constant curvature, the geometry is unique. The Riemann curvature tensor is a way to capture a measure of the intrinsic curvature. The reciprocal of the radius of curvature is called the curvature. A helix has constant non-zero curvature and torsion. Curvature and spheroidal shape of the earth is neglected. AAA is sufficient for congruence on a given curvature of surface. It produces rhizomelic short limbs, increased spinal curvature, and distortion of skull growth. A deeper analogy relates tidal forces with a property of surfaces called "curvature".