A couple of you have asserted that there are things in aikido that cannot be explained by physics, or at least by physics as we currently understand it. Can anyone point to a specific instance of this? That, I think, would hit the proverbial nail on the head and make this thread into a single coherent conversation.
I apologize to those of you two whom I have not replied specifically. There are so many responses here that I'd be up all night if I tried to quote them all and reply point-by-point.
Personally I think it'd be a great exercise.
It's all too easy to chalk a lot of this stuff as being "too complex" therefore...etc (though I agree, there are parts, especially with regards to breath pressure, tissue elasticity etc that would be much more complex to model accurately)
But there are some aspects of say, "Jin" or "Kokyu force" that can be explained using simple physics, and contrasted against how say maybe someone typically uses a force.
Maybe a good place to start would be how a typical person handles a push, versus how someone else with skills handles a push.
Just to get the ball rolling, I'd say the human body is designed to handle vertical loads efficiently. It tends to be uneconomical when a horizontal load is brought into play.
So one question would be, how do you efficiently deal with an incoming horizontal force (assuming its coming from a person).