11th
More on Stress from Wikipedia
Ok, I think stress is “the intensity of internal forces” in a body. So maybe in my current example, the external forces are gravity pulling all of the fluid down the inclined plane, and some friction acting on the bottom “layer” of the fluid, the part that’s in contact with the plane. The internal forces are the…friction, right? between different “particles” of the fluid. Though we’re supposed to be thinking of it as a continuum, so there are no particles.
But now I’m reading that “these internal forces are produced between the particles in the body as a reaction to external forces,” so maybe stress is actually the particles pushing against each other in a Newton’s laws kind of way. Geddes’s, Annie’s and my brief physics class did a problem once about pushing on a box that was in contact with second box. Maybe stress is like the continuum equivalent of the force box 2 was exerting on box 1 in that problem.
