1. The problem statement, all variables and given/known data I'm having a little trouble understanding how to derive the hydrostatic equations for fluid mechanics! My professor showed the derivation with respect to y in class, and it kind of made sense to me. Now I'm trying to see if I can derive the equation with respect to z and x. I think part of my issue is that I don't fully understand the forces that are acting on the fluid particle. I know there are two surface forces and one body force for the y derivation. My professor mentioned that there is only a body force for the y and z directions, but didn't mention x. He said the body force in this case is gravity, which I understand why this force would be on the particle in the z direction, but why the y direction or x direction? How is gravity affecting the particle from the y direction or x direction? Maybe the body force acting in the y direction isn't gravity? If its not what could it be and why is there no body force in the x direction? I'm not sure if I drew the forces correctly in the figure 2 for the z direction. I'm also not sure about how to draw the forces for the x direction, would that case just be two surface forces in the x direction? One coming from the front of the box towards the particle and the other coming from the back of the box towards the particle? The summation of forces part I understand no problem. If y'all could help me figure out how to get to that point I think I'll be good! From picture I attached: SF1 = (p-(∂p/∂y)(dy/2))dxdz SF2 = (p+(∂p/∂y)(dy/2))dxdz SF3 = (p-(∂p/∂z)(dz/2))dxdy SF4 = (p-(∂p/∂z)(dz/2))dxdy BodyForceInZ = (ρdxdydz)bf-z I hope my picture isn't too confusing, thanks for any help!!