附录Ⅰ 截面的几何性质 (Appendix Ⅰ Properties of plane areas) 1-1 截面的静矩和形心(The first moments of the area & centroid of an area) 1-4 转轴公式 (Rotation of axes) 1-2 极惯性矩 惯性矩 惯性积 (Polar moment of inertia Moment of inertia Product of inertia) 1-3平行移轴公式 (Parallel-Axis theorem)