The Calming Effect Of Oil On Surface Waves

THE CALMING EFFECT OF OIL ON SURFACE WAVES: MEASUREMENT OF THE EXTINCTION LENGTH BY LASER INTERFEROMETRY, Kimberly A. Cordray, William P. Griffin, Fred Behroozi*, University of Northern Iowa, Department of Physics, Cedar Falls, IA 50614, [email protected] The calming effect of olive oil on water has been observed since antiquity. Benjamin Franklin sparked interest in the phenomenon by making many experimental observations. Since his time, experimentalists have determined that oil forms a monomolecular layer on the water surface. It has also become generally understood that capillary waves play the major role in energy dissipation although the underlying mechanism is still poorly understood. One of the latest theories for the mechanism of the calming effect is that the capillary waves induce longitudinal, i.e. compressional, waves in the oil monolayer. The longitudinal waves produce sliding friction between the monolayer and the bulk water thus increasing the energy dissipation. This theory is in contrast to an older theory that the surface tension is the primary cause of energy dissipation. As an experimental verification of this theory, the attenuation of capillary waves on the surface of three fluids, two with a monolayer, were examined and compared to those of pure water. The experimental apparatus used a miniature laser interferometer, allowing noncontact measurements of the attenuation of capillary waves. The results show that the longitudinal waves are significantly more effective in damping compared to the surface tension alone, confirming the theoretical expectations of this mechanism.