Final answer:
When a fluid is flowing at a slow and constant rate within a long tube having a uniform diameter, the nature of the flow is laminar.
Step-by-step explanation:
When a fluid is flowing at a slow and constant rate within a long tube having a uniform diameter, the nature of the flow is laminar. In laminar flow, the fluid moves in smooth, parallel layers, with the velocity highest at the center and decreasing near the walls of the tube due to viscosity and friction. The flow rate remains constant along the tube, as the same amount of fluid must flow past any point in a given time to ensure continuity of flow.