.=drdt =-oRsin ati oR cos ati a=didt =-@2Rcos oti -@2Rsin wtj .2=-ORsin 2wi +oR cos 2aj a2 =-@'Rcos2wi -@2Rsin 2aj 两矢量相互垂直时应有 v.a=vacos0 =0 .a=(-oRsin ati +oRcos atj) .(-@2Rcosoti-@2Rsin otj) =0 .立La得证v dr dt    = R ti R tj   = − sin + cos a dv dt   = R ti R tj    cos  sin  2 2 = − − v R i R j t     =2 = − sin 2 + cos 2 a R i R j t     cos 2  sin 2 2 2 =2 = − − 两矢量相互垂直时应有 v a = vacos   = 0 v a ( Rsin ti Rcos tj)       = −  +  ( cos sin ) 2 2 R ti R tj    −  −  = 0 v a    ⊥ 得证