1. The problem statement, all variables and given/known data I have an empirically-derived equation for the shear stress of a fluid on a surface, given by the equation below. I am supposed to take the derivative of density with respect to distance, and I must use this equation to find an expression for density. Delta = Boundary layer thickness. Nu = Kinematic Viscosity u = Velocity Rho = Density 2. Relevant equations 3. The attempt at a solution I know the definition of shear stress for fluids (The second equation above). I've tried to equate it to the empirical formula, knowing that dynamic viscosity, mu, is just density*kinematic viscosity. The density variables cancel though. I can't have a tau term in the density expression, so I can't just algebraically manipulate the first equation to equal density.