= Quasi-static tether contraction
{title2=$E_{\rm rot}=L^2/(ml^2),\quad T=2L^2/(ml^3)$}
For two equal <point masses> $m$ joined by a light tether of length $l$, the central <moment of inertia> is $ml^2/2$. With conserved <angular momentum> $L$, the rotational <kinetic energy> is $L^2/(ml^2)$. Slow, smooth contraction gives $\dot E_{\rm rot}=-T\dot l$ with the displayed leading <tension>. The exact radial correction is $E_{\rm rad}=m\dot l^2/4$ and $T=2L^2/(ml^3)-m\ddot l/2$, so the total <work-energy theorem> remains exact for non-quasi-static schedules too.
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