It is long known that the Japanese and Chinese share quite diverse views on the matter of existant forces such as ki and chi. These differences however are merely cultural divides very recent, and overdue from an occupation and since lingering resentment of one population on another. The fact is, Japanese and Chinese culture, for as long as the former has existed, shared an influx of ideologies. Japanese martial arts, primordially, were emulated from northern style arts. When I strike, the energy flows from the ground, through my body, out my arm to the target. I believe chi is just kinetic energy, expediantly conducted through our bodies. Our bones, hollow, create conduits to minimize this force naturally for structural integrity against stresses, and so in certain positions and alignments, kinetic energy can flow more condusively and cohesively. Chi is the feeling of this utilization. It is the degree of control over channeling kinetic energy through oneself to another. Ki however, is a force which operates by binding two beings, one over the other. While many think kiai is to simply shout, it's really describing the bond created between two individuals by the sheer power of their being. Everyone has felt the presence of a master when they step in the square with them. Some have such great control over this bond, they can manifest this bond physically between themself and their desired subject. A quick search online gives a contemporary example of a man who can ring a bell by shouting. If you learn how to make a bowl of water ripple with your kiai, you've got the idea. But sound, too, is a physical force, and kinetic energy. The difference is how it is utilized, with ki directing it manifestly externally, and chi doing so through internal contact. Though they are indeed different, they both utilize the same element to gain control over the situation in totality, and ensure survival. And that is that they manipulate kinetic energy. When one can strike a series of touching, separate boards, and only break the last board, I would fear that man's strike.