1. The problem statement, all variables and given/known data Considering a unsteady, incompressible flow past a sphere placed in a channel. The sphere is offset somewhat from the center of the flow to destabilize what otherwise would be steady-state symmetrical flow. Calculate the tangencial rotational force at the sphere. 2. Relevant equations 3. The attempt at a solution My attempt is to make use of the Stoke's friction law for rotational motion of a sphere: [tex] F=-8 \pi \eta_0 a^3 \Omega [/tex] with [tex] \eta_0 [/tex] the viscosity, [tex] a [/tex] sphere radius, [tex] \Omega [/tex] sphere velocity. But this is the total force and I have to calculate only the tangencial.