Impact on Floating Membranes

We report on an experiment focusing on the wave dynamics triggered by the impact of a sphere on a floating elastic membrane. The thin rubber elastic sheet floats on a pool of water. After impact two distinct waves propagate. First a tensile wave propagates at the speed of sound in the elastic material. Behind the longitudinal wavefront the elastic membrane is stretched. A transverse wave, accompanied by fluid motion, propagates in the stretched region. The transverse wave presents a dispersion relation similar to capillary waves but the equivalent ``surface tension'' is the tension in the membrane, which results from the impact. We investigate the coupling between the two waves, documenting the variation of the ``surface tension'' with impact speed. The deceleration dynamics of the impactor and the instability of the membrane giving rise to wrinkles will also be discussed.