Underwater Cave Narrows: Continuity & Bernoulli Flow (2D)

This 2D companion strips the cave down to its cross-section and drives it with real fluid mechanics: a side panel lets you set the constriction ratio, inlet width, inlet flow speed, water density and viscosity, and the passage-width profile drawn on screen is the exact same function used to compute flow speed via continuity (A1v1=A2v2) and pressure via Bernoulli's equation at every point along the channel. Diver-tracer particles drift at the true local flow speed, visibly accelerating through the narrows while the live readout reports the speed-up factor, the pressure drop and the Reynolds number — the physics behind why a cave's narrowest passage is where currents turn dangerous.