Deborah number

The Deborah number is a dimensionless number which characterizes how "fluid" a material is. Even solids "flow" if they are observed long enough; the origin of the name is the line "The mountains flowed before the Lord" in a song by prophetess Deborah recorded in the Bible.

Formally, the Deborah number is defined as the ratio of the polymer characteristic relaxation time (lambda) and the flow characteristic time. The smaller the Deborah number, the more fluid the material.