2-21力系向一点简化 主矩M在三个坐标轴上的投影为 M0=∑M(Fl=∑M(F) Oy ∑ (26) 0z ∑M(F)2=∑M 主矩M。的大小和方向余弦分别为 M=y∑M(F+DMF+∑M(F cos(Mo,i)=∑M(F)/Mo (27) coMo,j)=∑M(F/M co(M,0)=∑M(F)/M

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