шестая степень скорости

Максимальный вес тела, увлекаемого потоком жидкости, пропорционален шестой степени скорости потока.

"In 1757, the German hydrologist Albert Brahms empirically observed that the submerged weight of objects that may be carried away by a river is proportional to the sixth power of the river flow speed.[7] This formulation is also sometimes called Airy's law.[8] Thus, if the speed of flow is doubled, the flow would dislodge objects with 64 times as much submerged weight."

-- http://en.wikipedia.org/wiki/River