Abstract: Methods and apparatus for non-invasive, simultaneous determination of density and a shear resistance relating variable of a non-gaseous, free flowing material are presented. In one example, the non-gaseous free flowing material is disposed within a vessel at a known or constant level. According to this example, the method and apparatus utilizes an adjustable mathematical model to determine the density and a shear resistance relating variable based on measurements of the system comprising the filling material, the vessel wall and the dynamic measuring instrument interacting with the wall.