The equation below represents a steady-state laminar flow of a fluid through a horizontal tube:
\[ \mu\,\frac{1}{r}\frac{d}{dr}\left(r\frac{dv_z}{dr}\right) - \frac{dP}{dz} = 0 \]
Figure: a horizontal cylindrical tube of radius R with fluid flowing along the z-axis; the radial coordinate r is measured outward from the tube's central axis and the axial coordinate z runs along the length of the tube.Here \(P\) is fluid pressure, \(\mu\) is dynamic viscosity, \((r, z)\) are the coordinates of a cylindrical polar system, and \(v_z\) is the axial velocity in the z-direction.
Which one of the following statements related to the above case is NOT correct?