Ockham's razor and modeling Particle(质点) A point with no shape and size ,but has mass Translational movement(平动) Each point of the body has the same trail in the motion Reference Frames(参照系)Particle（质点） Reference Frames（参照系） Translational movement（平动） Ockham’s razor and modeling A point with no shape and size ,but has mass Each point of the body has the same trail in the motion