Re: Is ki just good physics?
Musing on this, I realized that I actually have heard most about ki in my training from the first group I studied with. They were a Tomiki Aikido group under Merritt Stevens. Stevens Sensei (I don't know that he ever laid claim to the title of Shihan, tho he had the rank for it) taught aikido to LEO's across Ohio and the Midwest and was seriously badass; there was no tanking, fancy throws, or ribbons in his aikido.
Yet he and his students talked about using ki to make aikido waza work properly. I don't know that he had a deep theory of ki--if he did, I never heard him talk of it--but we would hear things like, "use your ki to nail his foot to the floor," or "send his ki right back at him," or "point your finger to direct your ki."
I think in the discussions here, we have some folks who are, perhaps, excessively spiritual and mystic in their use of ki--and we have others who, perhaps in reaction, are excessively material and unwilling to give any ground to the word or the concept.
But since I was introduced to the concept in a very grounded, practical way I've never worried about it or been embarrassed by it. It has always been just part of the landscape.