Making use of the concept momentum current intensity, the motion of objects including the falling of skydivers in damping medium was analyzed. The mechanics system of Der Karlsruher Physikkurs was introduced, where momentum and velocity were regarded as the central physical quantities. According to the definition analogy between force and current, the force was regarded as the momentum current strength. Mechanical problems was solved according to the continuity equation of momentum. The speed of the object falling in the air was calculated using this method and the reason for the existence of a minimum velocity for the skydiver with horizontal velocity before reaching the first closing speed was qualitatively analyzed. The study shows that the mechanics system of Der Karlsruher Physikkurs is not only feasible, but also effective. This can make people understand physics at a new height.