连续性方程continuity equation： 连续性方程的基础是质量守恒定律。无论什么运动形式，其总质量是不变的。The continuity equation is based on the law of conservation of mass. Whatever form of motion, the total mass is constant. 气体在管内流动过程中，系统质量保持守恒。The mass of the system remains conserved as the gas flows in the tube.