tregor even if the temperature is constant, you will still have rho = omega*length let me try one more time rho = omega*length lenght = length area = length^2 so R = (omega*length)*(length)/(length^2) = omega we still get R = omega which is correct regardless of rho being constant it still works. In the original post you eliminated rho and lumped it as a constant. can't do that.