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# Deborah number

The Deborah number is a dimensionless number, used in rheology to characterize how "fluid" a material is. Even some apparent solids "flow" if they are observed long enough; the origin of the name, coined by Prof. Markus Reiner, is the line "The mountains flowed before the Lord" in a song by prophetess Deborah recorded in the Bible (Judges 5:5).

### Additional recommended knowledge

Formally, the Deborah number is defined as the ratio of a relaxation time, characterizing the intrinsic fluidity of a material, and the characteristic time scale of an experiment (or a computer simulation) probing the response of the material. The smaller the Deborah number, the more fluid the material appears.

The equation is thus:

$De = \frac{t_\mathrm{c}}{t_\mathrm{p}}$

where tc refers to the relaxation time scale and tp refers to the time scale of observation.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Deborah_number". A list of authors is available in Wikipedia.
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