What are the small bubbles that form in a glass of water?

Ever found yourself wondering why there is always the odd bubble floating around the glass, even though you poured still water?

By Robert Matthews

Asked by: Bob Bullock, Swansea

Water contains dissolved air, molecules of which accumulate around tiny imperfections on the glass. This process of “nucleation” continues until a bubble forms, breaks free and rises to the surface. Dropping something light but crinkly like a lemon pip into fizzy water can trigger repeated cycles of nucleation and bubble formation, making it rise and fall repeatedly.

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