Abstract: The equations describing the flow of a viscoplastic fluid on a rotating disk are de-rived and are solved by perturbation technique and nurmerical computation respectivelyfor 2 cases. This makes it possible to calculate the thickness distribution of film. Twokinds of distribution of thickness have been found. For the viscoplastic fluid for whichboth viscosity and yield stress are independent of radial coordinate r, the thickness hdecreases with increasing r. For a Bingham fluid for which both viscosity and yieldstress are function of time and r. the thickness h increases with increasing r.

Key words: pendulum, multiple scale method, approximate potential, slowly varying parameter, flow on a rotating disk, viscoplastic fluid, thickness distributionof film