Further fluid dynamics

Last month we had whistling kettles, this month we have fluid dynamics giving new insights into the science behind foaming beer bottles. The experimental observations involve tapping the top of a newly opened beer bottle and then standing back as the suds foam out onto the floor. Apparently the sudden tap on the bottle’s mouth initiates compression and expansion waves causing bubbles to appear and quickly collapse. The cavitation-induced break-up of the larger bubbles creates clouds of very small "daughter bubbles," which grow and expand much faster than the larger mother-bubbles from which they split. The rapid expansion of these daughter bubbles gives the foam buoyancy.