F2 is defined as the force exerted by pressure P2 on an area ΔA in the negative j direction, while F1 is the opposing force from pressure P1 acting on the same area in the positive j direction. The discussion emphasizes the relationship between force and pressure, highlighting that F1 and F2 are equal in magnitude but opposite in direction due to the equilibrium condition of the system. The scenario involves a plane in a water container, where gravitational force acts downward, necessitating an upward force to maintain balance. The participants suggest that a visual representation of the setup would aid in understanding the forces involved. Ultimately, the proof hinges on the fundamental equation relating force and pressure, F = PΔA.
