Chapter 9 Linear Momentum and If no net external force acts on a system of particles, the total linear momentum of the system cannot change Discussion 1)守恒条件合外力为零F=∑F=0 当F<<F时,可略去外力的作用,近似地 认为系统动量守恒.例如在碰撞,打击,爆炸等问题中Chapter 9 Linear Momentum and Collisions If no net external force acts on a system of particles, the total linear momentum of the system cannot change. Discussion 1）守恒条件 合外力为零 当 时，可 略去外力的作用, 近似地 认为系统动量守恒 . 例如在碰撞, 打击, 爆炸等问题中. 0 ex ex =  = i F Fi   ex in F F   