Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Liquid Sculptures
[original media no longer available] Water sculptures–a marriage of liquids, photography, and timing–are spectacular form of fluid dynamics as art. Artist Markus Reugels is a master of the form. This video captures the life and death of such water sculptures at 2,000 fps, beginning with the fall of the initial blue droplet. The droplet’s impact…
Cornstarch Physics
Oobleck, a non-Newtonian fluid made up of water and cornstarch, is a perennial Internet favorite for its ability to dance and the fact that one can run across a pool of it. It’s typically described as a shear-thickening fluid and only exhibits solid-like behavior under impact. Strictly speaking, oobleck is a suspension of solid grains…
How Erosion Shapes a Flow
Erosion creates all manner of strange shapes as wind and water cut away at solids. But why does the interaction of the fluid and solid result in the geometries we observe? Above is a collage from an experiment in which a soft clay sphere was immersed in a water tunnel. After 70 minutes, the sphere had…
How Fast Do Holes Grow?
Taylor and Culick predicted a constant velocity for the rim of an opening hole in a soap film of uniform thickness. Unfortunately, it is difficult to experimentally produce a soap film of uniform thickness. It is much easier to create films of uniform thickness with liquid crystals in their smectic-A phase, in which the molecules…
Floating Water Bridges
Water bridges that seem to float on air are an electrohydrodynamic phenomenon. By filling two beakers with extremely pure deionized water and applying a large voltage across them, flow is induced from one beaker to the other, as seen in the first few seconds of the video above. This flow is stable enough that the…
The Vortex Under a Falling Drop
We take for granted that drops which impact a solid surface will splash, but, in fact, drops only splash when the surrounding air pressure is high enough. When the air pressure is low enough, drops simply impact and spread, regardless of the fluid, drop height, or surface roughness. Why this is and what role the…
Marangoni Flows
Differences in surface tension cause fluid motion through the Marangoni effect. Because an area with higher surface tension pulls more strongly on nearby liquid than an area of low surface tension, fluid will flow toward areas of higher surface tension. Here surfactants, shown in white, are constantly injected onto a layer of water dyed blue.…
Mixing Flows
Turbulence is an excellent mixer. Here two fluorescent dyes are injected into a turbulent water jet. Flow is from the bottom of the image toward the top. The dyes are quickly mixed into the background fluid by momentum convection, their concentration decreasing with increased distance from the source. Large-scale structures like the eddies visible in…
Fluid Sculptures From Bursting Bubbles
A bubble initiated near a free surface–like the air-water interface here–can generate some spectacular dynamics. Beginning at the far left, the expanding subsurface bubble causes a dome at the surface that sharpens into a spike. By Frame 3, the bubble is collapsing but overshoots and rebounds, which introduces the tiny instability in Frame 4 that…
Explosive Boiling
A superheated liquid can reach temperatures higher than its boiling point without actually boiling – similar to how liquids can be supercooled below their freezing point without solidifying. The photo sequence above shows how explosive the boiling of a superheated water droplet submersed in sunflower oil can be. Image (a) in the lower left shows…