Feeling through a film

Touch a liquid surface with a sharp needle and pull it gently – the force you exert is essentially determined by the surface tension of the liquid. This classical capillary phenomenon was revisited in a recent paper, published in Physical Review Letters, when a thin elastic film floats on the liquid surface. The presence of a film increases the force that is needed to poke the interface, as might be expected. Surprisingly, however, it is not the 3POKING newmechanical properties of the film that stiffen the interface, but rather the interplay between surface tension, hydrostatic pressure and the finite size of the sheet. This universal, material-independent response, is attributed to a novel geometrical concept that the authors call “asymptotic isometry”: Continue reading “Feeling through a film”