S Ar 0 r(计+△) 瞬时速度: r(t+△)-r(t)_dr 4->0∠tM0 △t dt dz≈ = x dt dt tui=vx+vy+vzh 注意:△s≠|△,ds=dF AF|≠△r,dF≠dr 1212 z v x v y v z t z y t y x t x v x y z = ˆ + ˆ + ˆ = ˆ + ˆ + ˆ d d d d d d t r v t 0 lim → = 瞬时速度: r s 0 r(t+t) r(t) t r t r t t r t t d d = + − = → ( ) ( ) lim 0 注意: s r , r r, dr dr d s dr =