Beer bubble math

The rate of change of bubble volume. If this quantity is positive, the bubble will grow; if it’s negative, it will shrink.

A constant that depends on the temperature and the specific gas in the foam. (The foam on top of a glass of Guinness lasts unusually long because Guinness uses nitrogen in addition to carbon dioxide in its beer. K is smaller for nitrogen, so the bubbles change size more slowly.)

The sum of the lengths of the edges of the surfaces where the bubble intersects other bubbles. For an isolated bubble, E is 0; for a big bubble surrounded by many little bubbles, it is la

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