Stout Proof Of Falling Bubbles
California - Scientists have shown that the bubbles in a pint of Guinness really do move down instead of up.
To mark St Patrick's Day, a team of Scottish and US researchers has produced video evidence to show the bubbles being dragged to the bottom of the glass. An earlier study concluded that the phenomenon may only have been an optical illusion. Close examination reveals that as the pint settles, bubbles touching the walls of the glass experience drag that prevents them floating up.
Bubbles in the centre of the glass, however, are free to rise. A circular flow is created, causing bubbles at the the edge to be pushed downwards on the inside surface of the glass. Eventually more and more bubbles find their way to the head of the beer until the cycle loses momentum. The effect occurs in any liquid, say the scientists, but the contrast between the dark stout and its creamy bubbles makes it easier to spot in Guinness.
The relatively small nitrogen bubbles in Guinness are also more easily pushed around and less able to dissolve than the carbon dioxide bubbles in soft drinks. The Scottish scientists worked in collaboration with colleagues led by Professor Dick Zare at the University of Stanford in California. They are the first to successfully capture the tiny, elusive bubbles on film, using a high-speed digital camera with a zoom lens in a chemistry laboratory. As well as settling pub debates, the video could help improve scientists' understanding of fluid dynamics in a wide range of areas, including industry, medicine and oceanography.
California - Scientists have shown that the bubbles in a pint of Guinness really do move down instead of up.
To mark St Patrick's Day, a team of Scottish and US researchers has produced video evidence to show the bubbles being dragged to the bottom of the glass. An earlier study concluded that the phenomenon may only have been an optical illusion. Close examination reveals that as the pint settles, bubbles touching the walls of the glass experience drag that prevents them floating up.
Bubbles in the centre of the glass, however, are free to rise. A circular flow is created, causing bubbles at the the edge to be pushed downwards on the inside surface of the glass. Eventually more and more bubbles find their way to the head of the beer until the cycle loses momentum. The effect occurs in any liquid, say the scientists, but the contrast between the dark stout and its creamy bubbles makes it easier to spot in Guinness.
The relatively small nitrogen bubbles in Guinness are also more easily pushed around and less able to dissolve than the carbon dioxide bubbles in soft drinks. The Scottish scientists worked in collaboration with colleagues led by Professor Dick Zare at the University of Stanford in California. They are the first to successfully capture the tiny, elusive bubbles on film, using a high-speed digital camera with a zoom lens in a chemistry laboratory. As well as settling pub debates, the video could help improve scientists' understanding of fluid dynamics in a wide range of areas, including industry, medicine and oceanography.
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