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A space curve; the vectors T, N, B; and the osculating plane spanned by T and N. In differential geometry, the Frenet–Serret formulas describe the kinematic properties of a particle moving along a differentiable curve in three-dimensional Euclidean space, or the geometric properties of the curve itself irrespective of any motion.
T is the unit tangent, P the unit normal, and B the unit binormal. A Frenet frame is a moving reference frame of n orthonormal vectors e i (t) which are used to describe a curve locally at each point γ(t). It is the main tool in the differential geometric treatment of curves because it is far easier and more natural to describe local ...
By analyzing the class of curves which lie on such a surface, and the degree to which the surfaces force them to curve in ℝ 3, one can associate to each point of the surface two numbers, called the principal curvatures. Their average is called the mean curvature of the surface, and their product is called the Gaussian curvature.
The normal curvature, k n, is the curvature of the curve projected onto the plane containing the curve's tangent T and the surface normal u; the geodesic curvature, k g, is the curvature of the curve projected onto the surface's tangent plane; and the geodesic torsion (or relative torsion), τ r, measures the rate of change of the surface ...
The curvature is taken to be positive if the curve turns in the same direction as the surface's chosen normal, and otherwise negative. The directions in the normal plane where the curvature takes its maximum and minimum values are always perpendicular, if k 1 does not equal k 2, a result of Euler (1760), and are called principal directions.
Animation of the torsion and the corresponding rotation of the binormal vector. Let r be a space curve parametrized by arc length s and with the unit tangent vector T.If the curvature κ of r at a certain point is not zero then the principal normal vector and the binormal vector at that point are the unit vectors
A polygon and its two normal vectors A normal to a surface at a point is the same as a normal to the tangent plane to the surface at the same point. In geometry, a normal is an object (e.g. a line, ray, or vector) that is perpendicular to a given object.
Assume that this surface is regular, meaning that the vectors r u and r v are linearly independent. Complete this to a basis { r u , r v , n }, by selecting a unit vector n normal to the surface. It is possible to express the second partial derivatives of r (vectors of R 3 {\displaystyle \mathbb {R^{3}} } ) with the Christoffel symbols and the ...