Why Guinness bubbles fall

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The Independent Online

It is more than just a load of old Blarney: the bubbles in a pint of Guinness move down, instead of up, contrary to the laws of physics. And scientists have come up with the proof to mark St Patrick's Day.

It is more than just a load of old Blarney: the bubbles in a pint of Guinness move down, instead of up, contrary to the laws of physics. And scientists have come up with the proof to mark St Patrick's Day.

A team of Scottish and US researchers produced, for the first time, video evidence to show bubbles being dragged to the bottom of the glass.

An earlier study concluded that the phenomenon may only have been an optical illusion. But close examination revealed that, as the pint settles, bubbles touching the glass experience drag that prevents them floating up. Bubbles in the centre are free to rise. A circular flow is created, causing bubbles at the edge to be pushed downwards on the glass.

The effect occurs in any liquid, the scientists said, but the contrast between the dark stout and its creamy bubbles makes it easier to spot in Guinness.

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