Built on Facts

Here’s a new feature for this website that I’m going to try out.  One of the daunting things about studying physics is the profusion of textbooks.  Some are terrible, most are mediocre, and a shining few are really excellent.  I’m going to keep a list of those books which I’ve used in my classes and [...]

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Famously there are these exercises called Fermi problems, which are basically questions designed to be solved only by reference to approximation and dimensional analysis.  They aren’t even necessarily physics problems - the canonical example is “How many piano tuners are there in Chicago?”.  The reason why they’re interesting to try to solve is because it [...]

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You’re standing around minding your own business when suddenly a mile or two away, a rocket launches into the air. It curves upward in a lazy arc and begins its descent toward you. This rocket has several pounds of high explosive in its tip and so you’d prefer to find a way to [...]

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Next semester I’m taking the graduate classical mechanics class, and so I’m trying to spend a little time this summer brushing up on my old undergraduate mechanics. It’s been about three years since I’ve had to do much of it, and I’ve dug out my old books and am working on some problems. [...]

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For a little lagniappe to the regular daily post, here’s a few things things I thought were really cool.
The world’s largest air vortex cannon. How far away can you blow out a candle? Unless you have a jet engine handy, probably not this far.
Hrm. Carl over at Mass is working on some [...]

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The Boston Globe has a beautiful retrospective on some of the most visually stunning photographs the Cassini probe has taken from the vicinity of Saturn. All of them are beautiful and I highly recommend the link so you can see all the images. This image is of Dione, Saturn’s 4th largest moon. [...]

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For the last few hundred years, one of the most fundamental principles in physics has been that energy is conserved. You simply can’t get it from nowhere. Every experimentally tested physical theory from Newton’s laws to Maxwell’s equations and beyond is completely consistent with energy conservation. Noether’s theorem makes the possibility of [...]

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Last Friday I saw M. Night Shyamalan’s film The Happening. (Don’t worry, no real spoilers follow.) Science types will squirm during a few parts. There’s really very few physics issues to complain about, but the biologists and biochemists will blow a gasket. I wouldn’t worry about it too much - it’s [...]

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On this date in history was one of the earliest known dates in history.
There’s lots of things we can date with certainty. In the last few hundred years most dates can be pegged pretty accurately. December 7, 1941 was the date of the Pearl Harbor attack. Nicholas I of Russia was born [...]

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Earlier I was killing a little time today by reading about MOND. It’s an ad hoc attempt at a solution so the galaxy rotation problem. Essentially the outer portions of galaxies rotate a lot faster than they should given the their visible mass distribution. The obvious solution is that there’s mass which [...]

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