Surface Films Compacted by Moving Water: Demarcation Lines Reveal Film Edges

Science  02 Oct 1970:
Vol. 170, Issue 3953, pp. 61-64
DOI: 10.1126/science.170.3953.61


When water flows under the edge of a surface film the large viscous shear stress at the edge prevents the film from spreading and raises a ridge on the water surface. Near the top of its downstream flank the ridge has an abrupt change in curvature that we see as a line on the water.