2.自然坐标系 e,(t) =v2= △e. dt e(t+△t) d a= d(ve) dt dt dv de e+ dt dr △e=e(t+△t)-e(t)2. 自然坐标系 t t d d e t s evv rrr == t ev t v a d )(d d d t r r r == )()(tt t tetteer r r =Δ + Δ − o P1 P2 Δθ Δθ )(t ter )(t + Δtter t e r Δs Δ t e ve t v d d d d t t r r +=