This document discusses hydrostatic forces on plane and curved surfaces. It explains that the total force on a vertical plane surface is the sum of the forces due to pressure at different depths. The force is equal to pressure times area. For curved surfaces, the horizontal and vertical force components must be calculated separately, then combined into a resultant force. The center of pressure is also introduced, which is the point where the total hydrostatic force can be considered to act. Examples are provided to calculate hydrostatic forces on different surfaces.