THANKS! But then
1. what does stress tensor look like for a non-equilibrium fluid? (The texts usually don't emphasis on on what kind of fluid is the stress tensor defined, why is that so? also, this definition of tensor is used everywhere, on obviously non-equailibirum fluids...)
2. Is...
AlephZero, thanks for your explanation, but I'm still a bit confused..
1. Why does a point in fliud have to be *at equilibrium*? If every point in a fluid is at equilibrium, then no point will be accelerated, thus no change of motion for the fliud... what about a turbulent flow?
2. Instead of...
In fluid dynamics, always when some textbook talks about stress tensor, there is a figure like this:
http://www.fea-optimization.com/ETBX/hooke_help_files/stress.gif
it shows how stress tensor is defined based on a small cubic volume.
I kind of understand why the shear stress τxz should be...
-- i know there were threads about reduced density matrix in this forum, but I am reading "Density-functional theory of atoms and molecules" by Parr R., Yang W., their notation is quite confusing to me... their notation is the same as shown in this page...