Fluid resistance In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) refers to forces acting opposite to the relative motion of any object moving with respect to a surrounding fluid. [Wikipedia: https://en.wikipedia.org/wiki/Drag_%28physics%29] Fluid Mechanics UCUM http://unitsofmeasure.org/ucum.html#para-44 ODM2 Units Type Controlled Vocabulary ODM2 Working Group A vocabulary for describing the type of the Unit or the more general quantity that the Unit represents.