Buckling instabilities can arise from competition between axial compression and bending in slender objects. These are not
restricted to solids, but also occur with fluids with free surfaces1–4, in geophysics5 and
in materials processing6
. Here we consider a
classic demonstration of fluid buckling7
.
When honey is poured from a sufficient
height, it approaches one’s toast as a thin
filament which whirls steadily around the
vertical forming a regular helical coil (illustrated with silicone oil in Fig. 1), a behaviour reminiscent of the coiling of a falling
flexible rope8
. We derive a scaling law that
predicts the coiling frequency in terms of
the filament radius and the flow rate.