Streamline flow means each liquid element passing through a point travels along the same path and with the same velocity as the preceding element. A streamline is the path whose tangent at any point gives the direction of flow there.

• Two streamlines cannot cross because the fluid cannot have two velocity directions at one point at the same instant.
• Greater crowding of streamlines indicates greater velocity.
• The trap is to treat a streamline as a physical tube wall instead of a velocity-direction curve.

Laminar flow is the layered flow of a liquid in which adjacent layers move with different velocities but do not mix with one another. The OCR uses laminar flow synonymously with streamlined flow and places it below critical velocity.

• It occurs at relatively low velocities.
• Different layers can move with different speeds while still remaining orderly.
• Students often think 'different velocities' automatically means turbulence, but layered non-mixing motion is still laminar.

Turbulent flow begins when the liquid velocity exceeds the critical velocity and the motion becomes disordered. In this regime, path and velocity change continuously and eddies are formed.

• Most of the external energy maintaining the flow is spent in producing eddies.
• Only a small part of the supplied energy remains available for forward motion.
• The trap is to define turbulence only by 'fast flow'; the irregularity and eddy formation are the real indicators.