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Regarding a recent dispute, it is emphasized that the usual proofs of thesymmetry of the stress tensor of fluids based on the theorem of angularmomentum may not be valid because an internal force and its reaction may not bealong the line connecting the interacting fluid particles, even down to thelevel of molecules. Derivation according to the theorem of the motion ofcenter-of-mass indicates an additional term representing the total moment ofinternal forces. This moment of internal forces is the origin of thenonsymmetry of the stress tensor of fluids and is in general nonzero as long asshear stress exists. Examples are analyzed with special attention to themechanism of gas viscosity, indicating the reasonableness and correctness of anonsymmetrical stress tensor suggested in the literature, at least for gases.

General nonsymmetry of the stress tensor of fluids: Further considerations