Folding of viscous sheets and filaments

We consider the nonlinear folding behavior of a viscous filament or a sheet under the influence of an external force such as gravity. Everyday example s of this phenomenon are provided by the periodic folding of a sheet of hon ey as it impinges on toast, or the folding of a stream of shampoo as it fal ls on one's hand. To understand the evolution of a fold, we formulate and s olve a free-boundary problem for the phenomenon, give scaling laws for the size of the folds and the frequency with which they are laid out, and verif y these experimentally.