Inextensible filament
= Inextensible filament
{title2=$|\mathbf r_s|=1$}
= Inextensibility
{synonym}
An inextensible filament keeps the length of every material segment fixed. With material <arc length> $s$, its centerline obeys $|\mathbf r_s|=1$ and has <unit tangent vector> $\mathbf t=\mathbf r_s$. A <filament tension> acts as a <Lagrange multiplier> for this constraint.