I find that Gozo Shioda Sensei's explanation of Ki works best for me - the Mastery of Uke's Balance!
This then makes it composed of time (timing), position vector (distance/position), momentum/energy, force (from Uke & Tori/Sh'te/Nage), and mind (conciousness)!
There is obviously a lot more to Ki, but this is all I can piece together.