For , particles rotate counterclockwise without radial expansion. The out-of-plane curl is two, and its area integral equals the counterclockwise circulation around the boundary.对于 ，粒子逆时针旋转而不沿径向扩张。垂直平面方向的旋度为二，其面积分等于沿边界逆时针方向的环流。
All particles have the same angular speed; outer particles move faster along larger circles. No particle crosses the gold circle, so flux is zero even though circulation is nonzero.所有粒子角速度相同，外侧粒子沿更大的圆以更高线速度运动。没有粒子穿过金色圆，因此通量为零，但环流并不为零。