Recent content by masshakar

I have a question about the Von Mises Stress Ellipse: http://upload.wikimedia.org/wikipedia/commons/4/48/Tresca_stress_2D.png I understand that this equation if a component is subject to more than just an axial stress, the effect must be account for. I also understand that the ellipse is...

Why is it that forces (for changes in pressure across a fluid) on the control volume are generally considered compressive? Even in the derivation of the Navier-Stokes equation, it is assumed that forces from fluid pressure will be compressive? Why?