(3)、内力的功 FA=-FB δW=FA·dF4+FB·da =F·d(4-) δW=FA·dFAB 刚体:d产4B=0 变形体:dTAB≠0d rAB 0 FA FB = − ( ) A A B F r r = d − A A B B W F r F r = d + d 刚体: 变形体: A AB W F r = d d rAB = 0 B A FA FB o A r B r AB r (3)、内力的功