PositionⅤ ector(位矢) P(x,y,z, t) For a cartesian system: r=xi+vi+zk Motion function(运动方程) F=()==x(t)i+y(t)j+z(0)kPosition Vector(位矢) r xi yj zk = + + r r t x t i y t j z t k = ( ) = = ( ) + ( ) + ( ) For a Cartesian system: Motion Function ( 运动方程): P (x,y,z,t ) i k j x y z (t0 ) r(t) (t ) z x y