$4\mathrm{.}1\mathrm{.}6$ WP $($SS$)$ Video A flow can be visualized by plotting the

velocity field as velocity vectors at representative locations in the flow

as shown in Video V$4\mathrm{.}2$ and Fig. E$4\mathrm{.}1.$ Consider the velocity field given

in polar coordinates by $v_r=-\frac{10}{r},$ and $v_{}=\frac{10}{r}.$ This flow approxi$-$

mates a fluid swirling into a sink as shown in Fig. P$4\mathrm{.}1\mathrm{.}6.$ Plot the velo$-$

city field at locations given by $r=1,2,$ and $3$ with $=0,30,60,$ and $90.$