There is a point (p,q) on the graph of $f\left(x\right)=x^2$ and a point $\left(r,s\right)$  on the graph of $g\left(x\right)=\frac{-8}{x}$ , where   $p>0$ and $r>0$. If the line through $\left(p,q\right)$  and  $\left(r,s\right)$ is also tangent to both the curve at these points, respectively, then the value of $p-r$ is ____