In happier news closer to home, Corwin successfully passed his green stripe exam in his tae-kwon do class. The exam consisted of several parts -- demonstrating command of the moves, sparring, and applying the moves to break a board. In this case, he was required to use an axe kick to do so. In his orange belt exam last year, he had some trouble -- he had to repeat the attempt many times. On this occasion, he got it in two tries.
This may still be too early to introduce him to McNair and Feld's work (expanded on by other people) on "The Physics of Karate". But in fact, it looks like he has gotten a good intuitive grasp of the basic requirement -- hit hard and fast.