Copyright Goodheart-Willcox Co., Inc. Chapter 14 Model Documentation, Analysis, and File Exchange 385 • Mass. A measure of the inertia of a solid. In other words, the more mass an object has, the more inertia it has. Note: Mass is not a unit of measurement of inertia. • Volume. The amount of 3D space the solid occupies. • Bounding box. The dimensions of a 3D box that fully encloses the solid. • Centroid. A point in 3D space that represents the geometric center of the mass. • Moments of inertia. A solid’s resistance when rotating about a given axis. • Products of inertia. A solid’s resistance when rotating about two axes at a time. • Radii of gyration. Similar to moments of inertia. Specifi ed as a radius about an axis. • Principal moments and X-Y-Z directions about centroid. The axes about which the moments of inertia are the highest and lowest. PROFESSIONAL TIP PROFESSIONAL TIP Advanced applications of solid model design and analysis are possible with Autodesk Inventor software. This product allows you to create parametric designs and assign a wide variety of physical materials to the solid model. Surface Continuity Analysis Surface continuity describes the type of transition formed between adjoining surfaces in a model. Surface continuity is discussed in Chapter 10. Depending on the type of model you are working with and manufacturing requirements, you may need to modify the curvature of the model to create a more smooth transition between surfaces. For example, if you are working with a surface model and continuity settings are available, you may need to adjust the settings to produce a more smooth contour. In AutoCAD, zebra analysis is used to graphically check for surface continuity. Zebra analysis is also referred to as zebra striping. The ANALYSISZEBRA command is used to conduct zebra analysis. When using this command, AutoCAD projects a map of zebra stripes onto the model. The fl ow of stripes from one surface to another is then checked to determine the surface continuity. Areas where the stripes line up indicate where the model has surface continuity. The purpose of zebra analysis is to simply check for the quality of continuity or fl ow between surfaces. It does not tell you how accurate the surface is or the quality of the surface constructed. However, good surface continuity is important in many modeling applications. You will typically want the model to have a smooth surface shape and avoid sharp changes in curvature. Figure 14-46. The MASSPROP command displays a list of solid properties in the AutoCAD Text Window.