Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Microjets and Needle-Free Injection
Some people don’t mind needles, and others absolutely detest them. But to replace needles with needle-free injections, we have to understand how high-speed microjets pass through skin. Given skin’s opacity, that’s tough, so researchers are instead using droplets as a model. If we can understand the dynamics of a microjet passing through different kinds of…
Whiffling Geese
This wild photograph shows a goose flying upside down with its head turned 180 degrees in a behavior known as whiffling. In this orientation, the bird’s typical lift characteristics are reversed, but as you can see in the video below, this doesn’t exactly make them fall out of the sky. I suspect the geese compensate…
Sea Sponge Hydrodynamics
The Venus’s flower basket is a sea sponge that lives at depths of 100-1000 meters. Its intricate latticework skeleton has long fascinated engineers for its structural mechanics, but a new study shows that the sponge’s shape benefits it hydrodynamically as well. The sea sponge’s skeleton is predominantly cylindrical, with tiny gaps that allow water to…
Hovering Hawk
Birds have a level of control in flight that would make any engineer jealous. This 2021 Audubon Photography Award winning video by Bill Bryant shows off the skills of a red-tailed hawk. On this occasion, the hawk is using strong winds coming off the Rocky Mountains to hover in place. Notice how active his wings…
Fish Versus Bird
You’ve seen birds catch fish, but have you ever seen a fish that catches birds? In this video, giant trevally fish hunt fledgling terns — including those in flight! To do so, the fish must correctly assess the bird’s speed and trajectory across the water interface, a feat reminiscent of the archer fish’s aim. They…
Leidenfrost Without the Heat
Leidenfrost drops slide almost frictionlessly on a layer of their own vapor, generated by extremely hot surfaces nearby. But in this experiment researchers recreated many of the classic behaviors of a levitating Leidenfrost drop without the added heat. Instead, they supersaturated water droplets with carbon dioxide to create “fizzy droplets” that slide and self-propel along…
Shattering With Resonance
Resonance is a phenomenon that is both familiar and somewhat mysterious. It takes place when a system is excited near its natural frequency. In this case, we’re seeing a mechanical resonance that’s driven by sound waves near the glass’s natural frequency. Once excited, the glass vibrates by flexing side-to-side along one axis and then again…
The Froghopper’s Incredible Suction
The tiny froghopper feeds on the sap in xylem, a feat that requires overcoming more than a megapascal of negative pressure. Plants, as you may recall, transport water and nutrients from their roots to their leaves through negative pressure, essentially pulling on the water as if it were a rope. So drinking that sap is…
“Starlit”
In “Starlit” filmmaker Roman De Giuli explores a universe in a fish tank. The planets and asteroids we see are droplets of paint and ink floating in a transparent, gel-like medium. I particularly like the sequences where paint stretches, beads up, and breaks into a string of droplets! (Image and video credit: R. De Giuli)
Fun From the Beach
Here’s a neat bit of fluid dynamics derived from a day at the beach! Our experiment begins with well-mixed (and likely compacted) sand grains and sea water in a bottle. When flipped, the sand layer sits at the top of the bottle with the water layer beneath. Very quickly new layers establish themselves in the…