Cauchy Stress Tensor for a fluid

[@yugzed2233]

Hi sir. I just want to clarify that when you said that t is invariant regardless of the position of the normal vector. So should it be t(n) = t(-n)? I can't seem to grasp why we need to add a negative, -t(n) = t(-n), when they should be equal?

[@leonardo.molinari69]

If you consider outer and inner volumes as 2 different entities, on a point on the boundary surface the force developed by the inner on the outer is opposite to the force developed by the outer on the inner. Intensity is obviously equal, but not the sign.