Posted at 7:21 AM on January 4, 2010
by Bob Collins
(0 Comments)
Filed under: Five by 8
Roofs and walls are both good examples of this. Wooden studs that make-up walls have one face close to the outside and one face close to the inside, usually with insulation in between. Roofs have a more complex structure built from rafters or wooden trusses shaped in the form of a triangle. The top parts are exposed to near-outdoor temperatures (the temperature of the vented attic space) and the bottom part is wrapped in insulation near the ceiling of the warm living space below. Parts of the structure therefore, are shrinking while others are staying essentially the same. The differential temperatures cause the wall or roof assemblies to distort in shape. In principle, these systems (walls and roofs) are designed and built so they stay in place and are connected to each other in a sturdy and relatively tight manner. While the connectors that provide this structural assembly vary (nails, screws, metal plates, etc.), they are designed to resist excessive movement while allowing for some expansion and contraction of the component parts. When components of a building shrink quickly, an extreme amount of stress is produced in the connections and joints.More science: Why does snow "crunch" when it's particularly cold? There's some debate about this, says Science Geek Girl. Are our shoes making the noise, or the snowflakes?
The mechanism behind all three is the same -- lubrication, good or bad. When snow does NOT crunch, then the grains / crystals in the snow are well lubricated. When snow DOES crunch, then lubrication is poor. The lubricant is of course water in all cases, coming from two sources, both of which are temperature-dependent:3) Over the weekend, I documented several poignant remembrances of Deborah Howell, the former Pioneer Press editor who was killed in New Zealand. The Washington Post, where she worked before her retirement a year ago, has a blog written by its obituary writers. Matt Schudel captured in one sentence, a most poignant moment:
Deborah's husband, C. Peter Magrath (pronounced McGraw), a three-time university president, courageously took my call because, as he said, Deborah told him he should never duck a reporter's questions.4) Pat downs, body screenings, and ABBA music played loud (to weed out the weak) are all part of new airport security rules for international flights to the U.S. Nate Silver of fivethirtyeight.com says it took him three hours to get from the airport door to his gate in Montreal over the weekend. That gave him plenty of time to do what he does best: Crunch the numbers on Violent Passenger Incidents (VPI):
I don't mean to be glib about the risk to the passengers on the jets themselves, but 12 out of every 13 innocent deaths on 9/11 were to people on the ground. And even if the deaths at the WTC and the Pentagon are included, the rate of deaths from Violent Passenger Incidents during the 2000s qualifies as relatively "normal", comparable to or slightly lower than the death rates in the 1940s through the 1980s. In fact, with the exception of the 1930s, when there wasn't really enough commercial air travel to provide for a sufficient sample size, and the 1990s, a decade which was a positive outlier in so many ways, the death rate from VPIs has been remarkably constant from decade to decade.Silver does not expect anything to change as a result of his research. "But let's at least analyze these trade-offs rationally, and not let the terrorists terrorize us any more than we must," he said. Good one.
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