普通物理学Ⅰ（H）7-Systems of Particles-14.pdf

Chapter 7 Systems of Particles 7-1 The motion of a complex object 2014-3-17 phypzq@zju.edu.cn 1 2014-3-17 1 Chapter 7 Systems of Particles qiugan 2014-3-17 phypzq@zju.edu.cn 2 2014-3-17 2 Chapter 7 Systems of Particles Two motions: 1. a translational motion of a special point that is called the center of mass. 2. a rotational motion about that point. Video—center of mass 2014-3-17 phypzq@zju.edu.cn 3 2014-3-17 3 Chapter 7 Systems of Particles 7-2 Two-particle systems Two parts: a system and its environment. External force: interactions between the system and its environment. Internal force: interactions between objects that are totally within the system. 2014-3-17 phypzq@zju.edu.cn 4 2014-3-17 4 Chapter 7 Systems of Particles The center of mass:   m r m r  1 1 2 2 r cm m m 1 2 Velocity of CM:   m v m v N  1 1 2 2 v    cm p m v