Thought for the month

“There is nothing noble in being superior to some other man. The true nobility is in being superior to your previous self.” Probably W.L. Sheldon, US lecturer on ethics (1858 – 1907) rather than Ernest Hemingway.

Thursday, 5 December 2013

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.

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