因ad=-.d=d(F·f)=d(r2)=dr 2r 2r 得W2=1-k(r-l k 即W, 12 2 子A 式中1=F1-1,O2=12-l 弹性力的功也与路径无关1 1 2 d d d( ) d( ) d 2 2 r r e r r r r r r r r r 因  =  =  = = 1 1 0 2 2 0 式中  = r −l , = r −l W k r l r r r ( )d 12 0 2 1 得 =  − − ( ) 2 2 2 2 12 =  1 − k 即 W 弹性力的功也与路径无关