Tank drainage looks like a trivial problem until you actually try to size a valve or predict how long a batch process will take — and then you're suddenly staring down Torricelli's law, discharge coefficients, and the awkward fact that flow rate isn't constant because the head keeps dropping as the tank empties.

This video from Ahmed Khalid walks through the fluid mechanics of gravity-driven tank drainage: how the height of liquid above the outlet drives velocity (v = √(2gh)), why drain time scales with the square root of initial height rather than linearly, and how valve geometry and the discharge coefficient (Cd) modify the idealized picture. It's the kind of foundational chemical/mechanical engineering topic that shows up constantly in process design, stormwater management, and even hobbyist projects like homebrewing or aquaponics.

What makes it worth watching over a textbook derivation is the connection to practical variables engineers actually tune — outlet diameter, valve position, tank cross-section — and how each one shifts the drain-time curve. For a 487-subscriber channel, this is a genuine attempt at teaching applied fluid mechanics rather than an animation reel.

The rest of today's crop was mostly Shorts, hashtag spam, or generic "how a motor works" explainers. This one at least commits to a specific, quantitative problem.