A two-dimensional perspective projection of a sphere

A sphere (from Greek σφαῖρα-sphaira, "globe, ball") is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point. This distance r is known as the radius of the sphere. The maximum straight distance through the sphere is known as the diameter of the sphere. It passes through the center and is thus twice the radius.

In 3 dimensions, the volume inside a sphere (that is, the volume of a ball) is given by the formula

where r is the radius of the sphere and π is the constant pi. (Our solved example in mathguru.com uses this concept)

http://en.wikipedia.org/wiki/Sphere

The above explanation is copied from Wikipedia, the free encyclopedia and is remixed as allowed under the Creative Commons Attribution- ShareAlike 3.0 Unported License.