DISK (MATHEMATICS)

A disk is the region bounded by a circle. An 'open disk' is the interior of the disk excluding the bounding circle, while a 'closed disk' (see closed set) is the open disk together with the bounding circle.

In geometry, a 'disk' (also spelt 'disc') is the region in a plane bounded by a circle.
A disk is said to be ''closed'' or ''open'' according to whether or not it contains the circle that constitutes its boundary. In Cartesian coordinates, the open disk of center (a, b) and radius ''R'' is given by the formula
:D={(x, y)in {mathbb R^2}: (x-a)^2+(y-b)^2 < R^2}
while the closed disk of the same center and radius is given by
:overline{ D }={(x, y)in {mathbb R^2}: (x-a)^2+(y-b)^2 le R^2}
The area of a closed or open disk of radius ''R'' is π''R''2 (see π).
The ''ball'' is the disk generalised to metric spaces. However, sometimes "disk" is used to mean "ball".
In theoretical physics a disk is a rigid body which is capable of participating in collisions in a two-dimensional gas. Usually the disk is considered rigid so that collisions are deemed elastic.

Contents
See also

See also



★ Unit disk, a disk with radius one

★ annulus (mathematics)

★ Disk algebra

This article provided by Wikipedia. To edit the contents of this article, click here for original source.

psst.. try this: add to faves
©2009 TripAtlas.com