Cone - Definition and Overview

A cone is a basic geometrical shape: see cone (geometry). Several things have also been called "cones" on account of their shape:

• A volcanic cone is a mountain formed by material ejected from a volcanic vent.
• In relativity, the light cone of an event consists of all spacetime events that can interact with it.
• The scaly fruit-like reproductive bodies of certain plants, especially conifers and cycads, are called cones: see conifer cones.
• In vertebrate anatomy, a cone cell is a type of light-sensitive cell found along with rods in the retina of the eye.
• In ceramics manufacture, a pyrometric cone is a conical or pyramidal mineral stick that is used to gauge the temperature of an oven.
• An ice cream cone is a container for ice cream, shaped like an inverted cone open at its top. It is often made of edible pastry.
• A traffic cone is a brightly colored cone-shaped plastic object commonly used as a temporary traffic barrier or warning sign.
• In basketball, a cone is a player who is so slow and unskilled, that can be dribbled as if he was a traffic cone.

The word cone and its derivatives also have several specialized meanings in mathematics:

• In geometry, cone is often used informally for conical surface, usually a right circular one.
• Also in geometry, the cone of an arbitrary set <math>X<math> means the union of all line segments connecting a fixed point to points of <math>X<math>. For exmple, this coning operation will turn a triangle into a tetrahedron.
• In topology, too, coning may be applied to a topological space, e.g. to define the barycentric subdivision of a cell complex; see cone (topology).
• In linear algebra, the convex cone of a set of vectors consists of all linear combinations of those vectors with non-negative coefficients.
• In graph theory, a cone graph is a graph with a universal vertex (a vertex that is connected to all others vertices).
• In descriptive geometry, "conical projection" is another name for the perspective projection.
• In cartography, however, a conical projection maps the spherical surface of the Earth to a conical surface, that is then unrolled onto a plane.
• A conic section is any curve obtained by cutting the surface of a cone (more precisely, a conical surface) by an arbitrary plane.