Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Drops on a Porous Surface
The splashing of a drop upon impact is a remarkably complicated phenomenon. Perhaps surprisingly, the air around the impacting drop plays a major role in determining which drops splash and which don’t. Lowering the air pressure, for example, stops a drop from splashing. The layer of air that gets trapped beneath the spreading edge of…
Phytoplankton Blooms
When the right nutrients come together in coastal waters, it can feed a phytoplankton bloom large enough to be visible to satellites. The phytoplankton themselves are microscopic organisms that are easily carried along by oceanic flows. In fluid dynamics terms, they are passive scalars or seed particles–additives that reveal the structure of the flow without…
Hummingbird Hovering
Hummingbirds have a unique way of flying among birds. By flapping in a figure-8 motion, they generate lift on both the upstroke and the downstroke, which enables them to fly forward, backward, and even hover for extended periods. Such mid-air acrobatics are necessary for a species that feeds on flower nectar. What is especially impressive…
The Dance of the Droplets
Milk and juice vibrating on a speaker can put on a veritable fireworks display of fluid dynamics. Vibrating a fluid can cause small standing waves, called Faraday waves, on the surface of the fluid. Add more energy and the instabilities grow nonlinearly, quickly leading to tiny ligaments and jets of liquid shooting upward. With sufficiently…
Cloud Formation
Clouds are so ubiquitous here on Earth that it’s easy to take them for granted. But there’s remarkable complexity in the mechanics of their formation. This great video from Minute Earth steps through the processes of evaporation and condensation that drive basic cloud formation. After evaporation, buoyancy lifts warm, moist air upward. That warm air…
Dead Water
Sailors have long known about the “dead water” phenomenon, which can bring ships to a near-standstill, but it was only within the last century that an explanation for the behavior was found. The underlying cause is a stratification of fluids of different densities. As seen in the video above, when a boat moves by exerting…
Why Joints Pop
Joints like our knuckles are lubricated with liquid called the synovial fluid. When manipulated, these joints can pop or crack audibly. For half a century, researchers have thought the cracking sound joints under tension make was the result of bubbles in the synovial fluid collapsing. But a new cine magnetic resonance imaging (MRI) study shows…
Espresso in Space
The International Space Station resupply mission launched yesterday included a long-awaited fluid dynamics experiment that offers astronauts a taste of home: the ISSpresso espresso machine. Built by two Italian companies, the specially-designed espresso maker contains a non-convectional heating system and high-pressure piping to safely enable proper brewing using real coffee while in microgravity. The machine…
Newtonian and Non-Newtonian Vortices
Not all vortex rings are created equal. Despite identical generation mechanisms and Reynolds numbers, the two vortex rings shown above behave very differently. The donut-shaped one, on the top left in green and in the middle row in blue, was formed in a Newtonian fluid, where viscous stress is linearly proportional to deformation. As one…
Growing Icicles
For those from colder climates, icicles are a familiar part of winter. They come in a multitude of shapes and sizes, many of which have been captured and cataloged in the Icicle Atlas project. The site contains images, videos, and measurements of more than 230 icicles grown in the lab over the course of four…