Different conventions exist for the signs of normal and shear stresses in fluid dynamics. Understanding how stresses act in fluids is a key to understanding the entire subject of fluid dynamics, and if the stress sign convention is not clearly set out, the danger is that the student battles through the subject in constant confusion about signs. This paper explains the conventions used in some of the most popular textbooks, compares them, and discusses briefly the advantages and disadvantages of each convention and the ramifications for the Navier–Stokes equations.

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2023
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