Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Chocolate Fountain
Amidst your holiday celebrations, you may have encountered a chocolate fountain. In a recent paper, applied mathematicians have laid out the physics behind these delicious decorations, and it turns out they are an excellent introduction to many fluids concepts. Molten chocolate is a mildly shear-thinning, non-Newtonian fluid, meaning that it becomes less viscous when deformed.…
Freezing From Below
Watch closely as a droplet freezes on a cold surface, and you’ll observe something surprising. First, a freeze front will appear, traveling upward from the substrate. It curves slightly near the edges, leaving a liquid cap atop the frozen drop. But, as we’ve all discovered, water expands as it freezes. We can watch the drop…
Swimming in Microgravity
For years, I have wondered what a fish swimming in microgravity would look like. Finally, my curiosity has been rewarded. Here is a sphere of water in microgravity, complete with a fish. Personally, I am impressed that, despite the fish’s best efforts, the surface tension of the water is strong enough to keep it confined.…
Falling Ink
Photographer Linden Gledhill created these nebula-like composites from photos of ink diffusing in water. The work was inspired by Mark Stock’s “Spherical Rayleigh-Taylor Instabilities” series featured here last week. Like Stock’s computational art, the twisted fingers and vortex rings above form due to the denser ink falling through less dense water. The interface between the two…
Helicopter Tip Vortices
Airplanes and other fixed-wing aircraft produce wingtip vortices as a result of their finite length. Rotor blades, like those on helicopters, produce the effect as well. Both wings and rotors generate lift by trapping low-pressure air on their top surface and high-pressure air below. At their tips, though, the high-pressure air can sneak around the…
Inside a Popping Bubble
Popping a soap bubble is more complicated than what the eye can see. In high-speed video, we find that the action is very directional, with the soap bubble film pulling away from the point of rupture. As it does so, waves, like those in a flapping flag, appear along the surface and strings of fluid…
Numerical Rayleigh-Taylor
If you’ve ever dripped food coloring or ink into a glass of water, you’ve probably created a cascade of tiny vortex rings similar to the images above. This is the Rayleigh-Taylor instability, in which the heavier ink/food coloring falls under gravity into the less dense water. What’s shown above is a special case–one that no…
“Monsoon II”
Every child learns about the water cycle in school, but an academic description of the process often lacks nature’s grandeur. In “Monsoon II” photographer Mike Olbinski captures the majesty of cloud formation and rainfall in a way that rekindles awe for the scale of the process. It begins with bright clouds popping up, the result…
Collecting Water in the Desert
Desert-dwelling plants like cactuses have to be efficient collectors of water. Many types of cactus are particularly good at gathering water from fog that condenses on their spines. Droplets that form near a spine’s tip move slowly but inexorably toward the base of the spine so that the cactus can absorb them. The secret to…
The Tightrope Dancers
Boiling is a process most of us don’t pay much attention to. But it can be remarkably entertaining and beautiful. This award-winning video shows boiling on and around a heated wire immersed in oil. Depending on the diameter of the wire and the power used to heat it, the researchers observe several different regimes of…