String length constraint
= String length constraint
{title2=$L(q_1,\ldots,q_n)=l$}
The <holonomic constraint> obtained by summing the straight and curved segment lengths of a taut <massless inextensible string> and setting the result equal to its fixed length $l$. <Differentiation> gives $\sum_i(\partial L/\partial q_i)\dot q_i=0$, a relation between the permitted <velocities>. A slack string does not impose this equality on endpoint separation.