https://www.google.ca/search?q=stre...m=isch&q=stress+tensor&imgrc=xK8-tGSPxXha7M%3 This is a simple question. -why stress is defined on 3 surfaces only instead of the entire 6 surfaces? I believe 3 surfaces are enough to explain the stress of a small cube. At static equilibrium, the opposite surfaces will experience the same stress but with the opposite direction. Is this right?