FYFD

Month: November 2019

  • Featured Video Play Icon

    Inside Tears of Wine

    Pour wine or liquor into a glass, give it swirl, and you can watch as droplets form and dance on the walls. This well-known phenomena, often called “tears” or “legs” in wine, results from an interplay of surface tension and evaporation. Despite its common occurrence, researchers are still discovering interesting subtleties in the physics, as seen in new research on the subject.  

    Dianna walks you through the phenomenon step-by-step in this video. The key piece of physics is the Marangoni effect, the tendency of regions with high surface tension to pull flow from areas with lower surface tension. In the wine glass, evaporation creates this surface tension gradient by removing alcohol more quickly from the meniscus than the bulk. That sets up the gradient that lets the wine climb the glass. By preventing or delaying that evaporation, we can see other neat effects, too, like shock fronts that travel through the film. (Video credit: Physics Girl; research credit: Y. Dukler et al.)

  • Shearing Grains

    Shearing Grains

    Granular materials, like beads and sand, demonstrate both solid and fluid-like behaviors, which makes them difficult to study. Traditionally, one method for studying how fluids respond to deformation places the fluid in a ring-shaped cell with a rotating outer wall. That creates a uniform shear, as indicated by the red arrows above. For granular materials, though, this classic set-up usually breaks the grains up into two separate regions, one that behaves solidly and the other that behaves fluidly.

    To get past that issue and study grains under truly uniform shear, researchers built a new version of the classic apparatus. In this new ring-shaped cell, the outer wall moves but so do independent concentric rings beneath the grains. This allows researchers to see how grains move under uniform shear (left) and what kinds of forces develop between jammed grains in the system (right). (Image and research credit: Y. Zhao et al.; via APS Physics; submitted by Kam-Yung Soh)