A basic model for the amount of energy required to lift an object a certain distance is given by E=Wh. Here, W is the gravitational force calculated by the object's weight, and h is the height to which the object must be lifted. A 20m high structure (as depicted in the following GeoGebra applet) is to be constructed from the ground up (i.e., built piece-by-piece, laying one small slab upon another). The structure is entirely solid, meaning that there are no gaps or hollow regions inside the structure. The black arcs serve as the corner boundaries of the structure and are formed from circles of radius 20. Specifically, the exterior walls of the structure run straight horizontally between the arcs at any given height. The arcs cross at the top of the structure and run perpendicular to each other. Selecting the "Reveal Cross Section" removes two of the exterior walls so that the horizontal cross-section can be viewed at any particular height. Notice that at any height, the cross-section is a square, and D gives the distance from the center of the area to one of the arcs