Definition:Radius

Disambiguation

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Radius may refer to:

• Geometry:
  • Radius of a Circle: a straight line segment whose endpoints are the center and the circumference of the circle.
  • Radius of a Sphere: a straight line segment whose endpoints are the center and the surface of the sphere.

• Radius of Regular Polygon:
  • Long Radius
  • Short Radius

• Analytic Geometry:
  • The radial coordinate of a point $P$ in a system of polar coordinates is also known as the radius of $P$.
  • Radius of Curvature|: the reciprocal of the absolute value of its curvature
  • Radius Vector

• Topology and Metric Spaces:
  • Radius of an $\epsilon$-Ball: In the open $\epsilon$-ball $B_\epsilon \left({x}\right)$ of the point $x$, the value $\epsilon$ is its radius.

• Analysis:
  • Radius of Convergence: The distance from the endpoints to the midpoint of the interval on which a power series is convergent.

• Graph Theory:
  • Radius of graph

• Mechanics:
  • Radius of gyration

Linguistic Note

The plural of radius is radii, pronounced ray-dee-eye.

This irregular plural form stems from the Latin origin of the word radius, meaning ray.

The ugly incorrect form radiuses can apparently be found, but rarely in a mathematical context.

The adjectival form radial usually means directed along a radius.

Internationalization

Radius is translated:

In French:

rayon

Also see

• Definition:Diameter
• Definition:Circumference