(4)作用在刚体上力偶的功 a(b×c)=b·(c×a) A=VB+ VAB vB+ OXrAB dW= Fa'dr1+ Fb'dr2 LAB B F(drdr B FA(vA-vB)dt =FA(0×PAB)dt O 0(rAB×FAdt -(omdt =+md0 55 (4)作用在刚体上力偶的功 dW = FA·dr1 + FB·dr2 = FA·(dr1-dr2) = FA·(vA-vB)dt = FA·(   rAB)dt =  ·(rAB FA)dt = (·m) dt =±md a·(bc) = b· (c  a) vA = vB + vAB = vB + rAB O r2 r1 A B FA rAB FB d