ROTATING RIGID RODS OR INCOMPRESSIBLE FLUIDS - HOW TO DETERMINE THE STRESS

When a fluid fills up a rotating box, the pressure inside the fluid is easily obtained by solving a closed set of equations. However, if the fluid is incompressible, the mass conservation equation is trivially satisfied and the pressure remains undetermined. After a preliminary a nalysis of the similar problem of a rotating rigid rod, this paradox i s removed by giving the fluid a small value of the compressibility chi and taking chi --> 0 at the end of the calculation. (C) 1998 American Association of Physics Teachers.