主矩在各坐标轴上的投影为 M0=[m(F小=∑m,(F) MO=∑m(F小=∑mF O=∑{m(F=∑mF) 主矩的大小和方向余弦为 M=VEm2(F)+区m,(F)+区m( cosa-2m(F) cOS B M ∑m,(h)cos=Md m(F主矩在各坐标轴上的投影为 矩在各坐标轴上的投影为 [ ] [ ] [ ]   = ∑ = ∑ = ∑ = ∑ = ∑ = ∑ M m ( ) m ( ) M m ( ) m ( ) M m ( ) m ( ) Oz O z z Oy O y y Ox O x x F F F F F F 主矩的大小和方向余弦为 矩的大小和方向余弦为 [ ] ( ) [ ( )] [ ] ( ) 2 2 2 MO = ∑mx F + ∑my F + ∑mz F O z O y O x M m M m M m ( ) cos ( ) cos ( ) cos F F ∑ F ′ = ∑ ′ = ∑ α′ = β γ