After over 30 years of studying Judo with some Karate, Tae-Kwan-Do, and Aikido thrown in from time to time, I have finally come to conclude that I have never seen a decent technical description of the physical principles surrounding the very specialized and effective techniques that martial arts have evolved over the centuries to protect people from injury when falling. Many practitioners are quite expert in the practice, and can teach the techniques quite effectively, but traditionally do not speak in any real detail on the scientific aspects. Frankly, I have found that this is a good thing, as the technical descriptions, even to MIT undergrads, have little impact on student improvement. But the study of different refinements and variations across different martial arts could be instructive. So I guess I'll write it myself and invite comment.In the interest of reaching the broadest possible audience, I will restrict this discourse to fundamental physical principles without any real mathematics, though possible later posts might go into specific numerical examples. In order to understand this discussion, readers should be, or make themselves, familiar with the basic physics surrounding velocity, acceleration, linear and angular momentum (and conservation thereof), ...
