1) With respect to my inner ear feeling an acceleration. There most
certainly is a preferred reference frame; namely the rest frame of the
structures that hold the fluid. And if the fluid accelerates wrt those
structures, one feels the acceleration; or if you prefer the pressure of the
fluid against those structures, at this level the distinction is semantic.
2) I've never seen a force sensor yet that doesn't work by first measuring
acceleration. Let's imagine that last springs discussion has been brought
up all over again (the Marlow chronicle's :-))) ). Although, I'm still
game; with limited time however.