This book has been written as a viewing platform to take a brief look at a world of full-fledged fluid dynamics equipped with a boundary condition for vorticity at an interface between two phases, based on new findings; 1. An angular momentum of fluid in a conceptual volume V is given by using spatial distribution of vorticity newly defined as a rotation of momentum vector. 2. A normal component of vorticity is exactly transferred from one phase to the other due to the shear force working at an interface between two phases. 3. The transportation of tangential components of vorticity is perfectly shut off at an interface, creeping flow solutions for surrounding and inner fluids are obtained for a spherical fluid particle settling or ascending in a simple shear flow. 4., A "fluffy and slippery" solution of the Saffman's equation for the first order inner expansion is obtained.5. A sum of the creeping flow solution and the "fluffy and slippery" solution is confirmed to be physicallysound near the particle's surface. By using the sum, forces acting on particle's surface, a horizontal migration velocity of the particle and a lift coefficient have been obtained as explicit functions.