= Uniform material thinning under planar-sheet tension
{title2=$h=h_0(z_0)-\Delta(t),\quad\Delta(t)=\int_0^tF(s)\,ds/(4\mu)$}
For a thin planar <viscous sheet> with zero effective gravity and prescribed tensile force $F(t)$ per unit transverse width, <force balance> gives $4\mu h w_z=F(t)$. <Conservation of mass> gives $D_th=-hw_z=-F/(4\mu)$, proving uniform subtraction from the initial material thickness. The material map satisfies $dz/dz_0=h_0/[h_0-\Delta]$. Thus the same material thinning creates greater extension wherever the initial sheet is thinner.
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