= Right-angle two-rod resistance matrix
{title2=$\binom{F}{G}=\mathsf R\binom{U}{\Omega}$}
For two perpendicular rods of length $2L$ joined at one endpoint, the <slender-body force density> gives translation resistance $CL\operatorname{diag}(3,3,4)$, rotation resistance $CL^3\operatorname{diag}(8/3,8/3,16/3)$, and translation–rotation block $CL^2\begin{pmatrix}0&0&-2\\0&0&2\\2&-2&0\end{pmatrix}$. The opposite block is its transpose. Here $G$ is the <torque> about the joint and $F$ the <force> on the fluid. Integrating along each rod proves the entries and makes the <symmetry and positivity of a rigid-body resistance matrix> explicit.
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