Past exam of the mathematics course of the University of Cambridge / 2014 / ib / Paper 2 / 7B / iii

Here $u=v=x-y$. The streamlines are $x-y=\text{constant}$, straight lines parallel to $(1,1)$. The entire line $x=y$ is stationary. On the $x-y>0$ side the motion is northeast, and on the $x-y<0$ side it is southwest. In orthonormal coordinates $p=(x+y)/\sqrt{2}$, $q=(x-y)/\sqrt{2}$, the velocities are $\dot{p}=2q$, $\dot{q}=0$: this is simple shear flow. The right panel shows both moving families and the stationary line.