Get a flu shot, sure. How about covering your damn mouth and nose when you sneeze? Yecch.
Monthly Archives: April 2009
What Goes Up Must Come Down
The PRL from the ArXiv paper I linked to in Follow the Bouncing Atom has been published.
Phys Rev Focus has a story on it
Fun with Integral spin
Built on Facts: Bose-Einstein Condensates, pt. 1
Part 2 and part 3
Some Pig
Bacon sandwich really does cure a hangover
I never needed to have a hangover as an excuse for a bacon sandwich. Bacon on toast is one way of undoing the damage of overcooked, super-crispy bacon (I prefer bacon that can’t be snapped in half like a dry twig)
Fun with Magnets
I’ve done several of these, including a version of the homopolar motor. The eddy current damping is fun, too — you can make nonmagnetic metals react to magnets by inducing current flow in them. Lenz’s law.
The UnReagan Effect
Putting UP a big wall. 6,000 km along the Sahara.
BLDG BLOG: SAND/STONE
Clarifying the biochemical process through which his project could be realized, Larsson explained in a series of emails that his “structure is made straight from the dunescape by flushing a particular bacteria through the loose sand… which causes a biological reaction whereby the sand turns into sandstone; the initial reactions are finished within 24 hours, though it would take about a week to saturate the sand enough to make the structure habitable.”
Coincidence? I Think Not!
(OK, I do, actually)
More Ideal Gas Demonstrations
A mole of an ideal gas takes up 22.4 L at STP. Burning a hydrocarbon makes lots of H20 and CO2; the latter is 1-for-1 with the oxygen in the air, but the water is 2-for-1. Plus the heating, which causes the expansion or pressure increase. But I’d like to see what happens after a little time has elapsed and the gases cool off and the water condenses. I suspect you need to hook the tire up to a compressor really soon — this is a trick to seat the tire on the rim.
Our Top Men Are Working on It
The Onion: NASA Embarks On Epic Delay
Top officials at the National Aeronautics and Space Administration unveiled plans this week for a comprehensive, multibillion-dollar delay—the agency’s most ambitious postponement of cosmic exploration ever.
The unprecedented delay has reportedly brought together the nation’s foremost aerospace engineers, whose combined efforts have already added 18 months of rescheduled meetings to the daring mission
No Grace Under Pressure
Atmospheric pressure is about 10 N/cm^2, but there are a whole lot of square centimeters on that tanker — the more familiar unit is N/m^2 (Pascals), where 1 atmosphere is 101325 Pa (or possibly even more familiar 14.7 psi).
Various sites showing this have claims about this happening after the tanker had been heated (from steam cleaning), and all the valves shut while it was still hot. One claims frozen (perhaps they mean liquid?) nitrogen being added. Plausible? Heating the tanker to 373K and then letting it cool to ambient should drop the pressure by 0.20 atmospheres. A tanker that’s 2 meters in radius and 10 m long has a surface area of 125.6 m^2, for a total force of 12.7 MegaNewtons. 20% of that is a lot. I don’t think the liquid nitrogen is strictly necessary, but would add to the effect.
The heat of vaporization of liquid nitrogen is 5.56 kJ/mol and its specific heat capacity of the gas is 29 J/mol-K. The volume of 125.6 m^3 means 5600 moles of an ideal gas, requiring 160 kJ/K to cool it down. Each liter of liquid nitrogen (29 moles) takes about 160 kJ to boil off, and then another .84 kJ per degree as the gas heats up from 77K. So ten liters of liquid nitrogen dumped into it will cool it about 20-25 degrees, depending on the starting point of the tanker. So that won’t hurt, but what’s probably more important is that the tanker was built to withstand some pressure difference and we see the catastrophic failure when its critical pressure difference is exceeded. Unlike the kind of test you can easily do with a can where you boil some water inside, seal it and watch it crumple as it cools, because it wasn’t designed to withstand and significant pressure difference.