As a child, I always loved watching rain on the windows as I rode in the car. Hemispherical droplets got stretched by the wind flowing over them. But they never stretched smoothly; instead they seemed to shiver and shake unevenly. A recent study looks at a similar situation: drops of glycerin forced to slide along a horizontal surface under the force of the wind. Like the drops on my parents’ car, the glycerin gets stretched out into an elongated oval. Surface waves develop atop the drop and move downstream. The drops, the authors observe, move a bit like a crawling caterpillar, pilling up and smoothing out as they move. (Image credit: rain – A. Alves, experiment – A. Chahine et al.; research credit: A. Chahine et al.; via APS Physics)
