The streamlines for an incompressible, inviscid, two$-$dimensional flow field are all concentric circles, and the velocity varies directly with the distance from the common center of the streamlines; that is:

$v_{}=Kr$

where $K$ is a constant. As we said in the class, this flow is a rotational flow. We also said that we cannot define a velocity potential for a rotation flow field. Prove this statement by showing that it is impossible to find a velocity potential for this flow.