Dimensionless number

In dimensional analysis, a dimensionless number (or more precisely, a number with the dimensions of 1) is a pure number without any physical units; it does not change if one alters one's system of units of measurement, for example from English units to metric units. Such a number is typically defined as a product or ratio of quantities which do have units, in such a way that all units cancel.

Related Topics:
Dimensional analysis - Number - Physical unit - Metric unit - Product - Ratio - Quantities

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For example: "one out of every 10 apples I gather is rotten." The rotten-to-gathered ratio is (1 apple) / (10 apples) = 0.1, which is a dimensionless quantity.

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Dimensionless numbers are widely applied in the field of mechanical and chemical engineering.

Related Topics:
Mechanical - Chemical engineering

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The CIPM Consultative Committee for Units toyed with the idea of defining the unit of 1 as the 'uno', but the idea was dropped. http://www.bipm.fr/utils/common/pdf/CCU15.pdf http://www.bipm.fr/utils/common/pdf/CCU16.pdf http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15588029&query_hl=3

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http://www.iupac.org/publications/ci/2005/2703/bw1_dybkaer.html

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