Divergence measures local net outflow. For the radial field , the outward flux through a radius- circle equals its area times the constant divergence, two.散度度量局部净流出量。径向场 穿过半径为 的圆周的向外通量，等于圆面积乘以恒定散度二。
Particles separate as they follow the radial field. The gold circle is a fixed boundary: outward velocity there has magnitude , so integrating around its circumference gives .粒子沿径向场运动时彼此远离。金色圆是固定边界，其上向外速度大小为 ，沿圆周积分即得 。