This fraud number plays a very important role, particularly if we look at the motion of a ship inverter or any some other body. The fraud number plays a very significant role and more important are the problems as to assure to the dams channels and spillways. This fraud number plays a very important role because here the surface elevation plays significant role rather than and the gravitational flows the significant role. Then, even if there is the viscous force, this is what fraud number importance. Now, another number of this type is what we call the Reynolds number.