Kerosene is pumped through a smooth tube with inside diameter \(D=30 \mathrm{~mm}\) at close to the critical Reynolds number. The flow is unstable and fluctuates between laminar and turbulent states, causing the pressure gradient to intermittently change from approximately \(-4.5 \mathrm{kPa} / \mathrm{m}\) to \(-11 \mathrm{kPa} / \mathrm{m}\). Which pressure gradient corresponds to laminar, and which to turbulent, flow? For each flow, compute the shear stress at the tube wall, and sketch the shear stress distributions.