Abstract: It is commonly considered that the mechanical properties of the slurry are different from that of ordinary Newtonian fluid, and can be described by that of Bingham fluid. Hence its shearing stress should be described by the formula of the shearing stress of Bingham fluid. But the author holds the contrary opinion and firmly believes that the slurry is a highly viscous fluid with very long relaxation time such as those of asphalt, glass, etc. In this article, we have discussed the mechanical properties of the slurry and the resistance of a sphere moving with uniform velocity in the slurry. In the process of discussion, we use Stokes solution of the viscous fluid passing around a sphere. When the sphere is in equilibrium under the action of gravitational force, the force of buoyancy and the resistance, we get the velocity of sedimentation. When the velocity of sedimentation is equal to zero, we get the relation between the yield stress of Bingham fluid and the diameter of the particles which will not sink. The theoretical results calculated are compared with the experimental data of Northwest Institute of Hydrotechnical Research and Institute of Hydraulic Research, Yellow River Conservancy Commission. They are congruous.

Key words: diffusion, symplectic mapping, asteroid