# Difference between revisions of "Torus"

DavidB4-bot (Talk | contribs) (→Topology: Spelling/Grammar Check & Cleanup) |
(Converted to math formulae) |
||

Line 2: | Line 2: | ||

A '''torus''' is the mathematical term for a tire-like shape created by rotating a [[circle]] around the [[x-axis]]. | A '''torus''' is the mathematical term for a tire-like shape created by rotating a [[circle]] around the [[x-axis]]. | ||

− | If the “inner [[radius]]” (the width of the doughnut hole) is R, and the radius of the circular cross-section is r, then, the [[surface area]] of the torus is | + | If the “inner [[radius]]” (the width of the doughnut hole) is <math>R</math>, and the radius of the circular cross-section is <math>r</math>, then, the [[surface area]] of the torus is |

− | :S = 4 | + | :<math>S = 4 \pi^2 (R+r)r</math> |

and the [[volume]] is | and the [[volume]] is | ||

− | :V = 2 | + | :<math>V = 2 \pi^2 (R+r)r^2</math> |

## Latest revision as of 14:16, 14 December 2016

A **torus** is the mathematical term for a tire-like shape created by rotating a circle around the x-axis.

If the “inner radius” (the width of the doughnut hole) is , and the radius of the circular cross-section is , then, the surface area of the torus is

and the volume is

## Topology

In topology, a **torus** can be defined as the cartesian product of 2 circles. It can be constructed from a rectangle by identifying its opposite edges under the quotient topology.

This means that the torus surface is connected in the same way as the points on a rectangle, where you can “wrap-around” from one side of the rectangle to the other. This was a common topology used in the playing field of older video games.

The genus of a one-fold torus is 1.

Unusually, it is possible to divide a torus into seven different colored areas such that each area borders the other six. This is not possible on a flat surface or a sphere, where the maximum number of areas that can all touch each other is four.^{[1]}