If you look closely at a glass of freshly poured Guiness (or any beer--but it's easier to see in a dark ale), you'll notice that some of the bubbles are actually falling instead of rising. Explain how this is possible.

In Technology Review (10/1/1997), Steve Nadis wrote:

"Small particles suspended in a liquid are constantly buffeted by collisions with other molecules, causing them to jiggle erratically in a manner known as Brownian motion. The phenomenon - first observed by botanist Robert Brown in 1824 and later described theoretically by Albert Einstein - is ubiquitous in nature, an inevitable consequence of thermal energy in the environment...gravity will cause most particles to drift downhill. But owing to Brownian motion, some occasionally will go uphill." 

 

 

 

 

Edited on January 12, 2005, 2:20 pm

Posted by Penny on 2005-01-12 14:18:13