There's eye-contact, eye-flicks, breath, timing...lots that physics doesn't begin to discuss. Not that I intend to get all foo-foo on yo' ass, just that they're not physics' thing
Not quite true, you could still use physics to describe the movements of the uke under these conditions, just not to accurately describe the cause of the movement unless you go very outre and make analogies between viscosity and intention etc. etc.
Basically, if there's a measurable effect and you don't mind too much what you use as your units of measurement, yes you probably could develop an equation to cover breath, certainly timing et al.