Physics on a Bar Stool

Hi, Matt:

When my boyfriend drinks beer out of a glass, he puts a paper coaster or the like on top of the glass to cover the opening. He says it keeps his beer colder longer. I never thought of glass or paper as an insulator, but a lot of things don't always make sense to me, especially after a couple of beers. What do ya think?

-- Tipsy in San Diego

Hi, Tipsy. Your boyfriend Dipsy has things a little confused. Paper (in layers) does make pretty good insulation, but he'd have to wrap his beer in an entire issue of the Reader to have it work very well. Once it's poured, his beer is constantly gaining heat on all surfaces, the glass and the beer, until the funky bar air and the beer are the same temperature. The cold isn't escaping from the top. My guess is, Dipsy got this trick from his dad. But I'll bet Dad did it because he thought it kept the beer from going flat. This old, old bar trick might keep your beer a little fizzier if you abandon it to shoot some pool (beer gas escapes until the beer and the air above it are equally saturated), but after the first three or four, who can tell the difference anyway? Bars are pretty much like the real world, just with more drunks and fewer physicists.