# Dimension

Pronunciation: /dɪˈmɛn.ʃən/ Explain

A dimension is an extension in a particular direction. A line has one dimension, since it extends in only one direction. A two dimensional space has two dimensions. An x-y graph is two dimensional. The x-axis defines one dimension and the y-axis defines another.

A dimension is not necessarily length. A dimension may also be temperature, time, mass, electrical current and others. For example, an equation may relate time and temperature: p = 2.5t where p represents temperature and t represents time. In this equation, one dimension is time and the other dimension is temperature. Albert Einstein's special theory of relativity deals with four dimensions: three dimensions are lengths making up a space, and one dimension is time. See also Dimensional Analysis.

### Dimensionless

An object is said to be dimensionless if it has no dimensions. The only object in most geometries that is dimensionless is a point.

Dimensions
Number
Dimensions
ManipulativeDescription
0-D
A point has no dimensions.
1-D
1 dimensional
A line has one dimension.
2-D
2 dimensional
A two-variable Cartesian coordinate system has two dimensions.
2-D
2 dimensional
A rectangle has two dimensions (length and width).
3-D
3 dimensional
A three-variable Cartesian coordinate system has three dimensions.
3-D
3 dimensional
A sphere has three dimensions (length, width, and height).
4-D
4 dimensional
Euclidean space/time has four dimensions (length, width, height, and time).
Table 1: Dimensions
1. McAdams, David E.. All Math Words Dictionary, dimension. 2nd Classroom edition 20150108-4799968. pg 61. Life is a Story Problem LLC. January 8, 2015. Buy the book

• McAdams, David E.. Space. allmathwords.org. Life is a Story Problem LLC. 3/12/2009. https://www.allmathwords.org/en/s/space.html.
• Euclid of Alexandria. Elements. Clark University. 9/6/2018. https://mathcs.clarku.edu/~djoyce/elements/elements.html.

McAdams, David E. Dimension. 4/19/2019. All Math Words Encyclopedia. Life is a Story Problem LLC. https://www.allmathwords.org/en/d/dimension.html.

### Revision History

4/19/2019: Updated equations and expressions to the new format (McAdams, David E.)
1/5/2019: Added vocabulary links, corrected order of dimensions in table. Corrected size of Geogebra Apps. (McAdams, David E.)
12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)