Moving fluid carries energy simply by moving, and there are two customary ways to quote it. Both describe the identical physical fact; they differ only in the currency.

The first is dynamic pressure: $q = \tfrac{1}{2}\rho v^{2}$ — read aloud q equals one-half rho v squared. $q$ is the dynamic pressure in pascals, $\rho$ is the fluid's density in kg/m³, and $v$ is the flow velocity in m/s. Push the units through: kg/m³ times m²/s² leaves kg/(m·s²), and that is a pascal exactly. It is the kinetic energy of the flow per unit VOLUME, and it is what a pitot tube feels when it brings the flow to a standstill against its nose.

The second is velocity head: $h_v = \dfrac{v^{2}}{2g}$ — h-v equals v squared over two g, with $h_v$ in metres, $v$ in m/s and $g$ at 9.81 m/s². Run the unit check again: m²/s² divided by m/s² leaves metres, every second cancelling. And notice the density has vanished. Velocity head is the same for water, oil or brine at the same speed — which is precisely why pump and duct people work in head and leave pressure to the gauges.

The habit worth building here is the unit check itself, and the doctrine that goes with it: units guide, they do not confess. If the units refuse to cancel into the answer's units, the rearrangement is wrong and there is no appeal. Units that DO work out never prove you right — plenty of wrong expressions have tidy units. The check runs one way only. And one last observation to keep in your pocket: both relations carry $v^{2}$, so doubling the velocity quadruples both. That single fact is why oversized pumps and undersized pipes are expensive in a way that surprises people.