In geometry, an intrinsic equation of a curve is an equation that defines the curve using a relation between the curve's intrinsic properties, that is, properties that do not depend on the location and possibly the orientation of the curve. Therefore an intrinsic equation defines the shape of the curve without specifying its position relative to an arbitrarily defined coordinate system.
The intrinsic quantities used most often are arc length, tangential angle, curvature or radius of curvature, and, for 3-dimensional curves, torsion . Specifically:
- The natural equation is the curve given by its curvature and torsion.
- The Whewell equation is obtained as a relation between arc length and tangential angle.
- The Cesàro equation is obtained as a relation between arc length and curvature.
The equation of a circle (including a line) for example is given by the equation where is the arc length and the curvature.
These coordinates greatly simpilfy some physical problem. For elastic rods for example, the potential energy is given by
where is the bending modulus . Moreover, as, elasticity of rods can be given a simple variational form.
Famous quotes containing the words intrinsic and/or equation:
“The permanence of all books is fixed by no effort friendly or hostile, but by their own specific gravity, or the intrinsic importance of their contents to the constant mind of man.”
—Ralph Waldo Emerson (1803–1882)
“Jail sentences have many functions, but one is surely to send a message about what our society abhors and what it values. This week, the equation was twofold: female infidelity twice as bad as male abuse, the life of a woman half as valuable as that of a man. The killing of the woman taken in adultery has a long history and survives today in many cultures. One of those is our own.”
—Anna Quindlen (b. 1952)