结合小球与均质自由杆的完全弹性碰撞、完全非弹性碰撞以及一般非弹性碰撞结果，指出球、杆碰撞问题中杆的瞬心的存在，证明了该瞬心位置的唯一性.并从力学原理上对瞬心做出解释.

Combining with the complete elastic collision，completely inelastic collision and general inelastic collision results of the ball and the homogeneous free rod，we point out the existence of the instantaneous center of the rod in the collision of the ball and the rod and prove the uniqueness of the instantaneous position.The instantaneous center used in the principle of mechanics is explained，too.