变力的功dW=F·dF Fcos e W= F dr F cos edr 合力的功=分力的功的代数和O W=∑Fd=∑∫Fd=∑W F=Fi+Fj+Fk dr=dxi +dvi+dzk W=「Fdx+∫Fy+∫Fdz W=w++wd cos d B B A A W F r F r =  =    合力的功 = 分力的功的代数和 i i i d d i W F r F r W =  =  =      W F x F y F z = + + x y z d d d    W W W W = + + x y z F cos A r B dr r r o 变力的功 d d W F r =  d d d d r xi yj zk = + + F F i F j F k = + + x y z