Theorem: The force on a submerged vertical plane area equals the product of the weight per unit volume, the submerged area, and the depth of the centroid of the area below the surface

F=wAy

What force must be withstood by a vertical dam 80ft long and 20ft deep? Ans. 500 tons What force must be withstood by a trapezoidal dam 100ft long at the top, 80ft long at the bottom, and 20ft deep? Ans. 17,333w