Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Supercritical
Supercritical fluids are neither a gas nor a liquid. The video above shows a tube of pressurized xenon, initially below its boiling point of approximately ~16 deg C. As the temperature is raised, you see the meniscus that marks the liquid xenon disappear. At this point, the xenon has transitioned into the supercritical state. It…
Swirling Pollen
This photo captures the chaotic mixing present in a simple puddle. Pine pollen strewn across the puddle’s surface acts as tracer particles, revealing some of the motion of the underlying water. As wind blows across the puddle, it moves the water through the formation of ripples and by shearing the surface. That deformation on the…
Pelican Surfing
Birds can be incredibly clever about using their surroundings to enhance their flight. Pelicans will even surf! As a line of waves rolls toward shore, it pushes a small updraft ahead of it – just like a line of mountains creates a windy updraft. Pelicans save energy by riding the updraft just like a surfer…
Fluorescein Ghosts
Fluorescein is a popular chemical for flow visualization, and, as this video from Shanks FX demonstrates, it’s not hard to extract from highlighters if you’d like to experiment with it yourself. Fluorescein can also be purchased in powder form, but it’s typically rendered into a dye before use. When dripped into water, it can leave…
Non-Newtonian Splashes
What happens when a stream of liquid falls through a screen? As the above video shows, water creates a beautiful flower-like burst of fluid when it hits a screen. Adding a little polymer to the water makes it non-Newtonian and more viscous. When hitting the screen, this slows it down but doesn’t prevent the fluid…
Reflecting in a Stream
Total internal reflection traps three lasers in a stream of falling water. When light tries to pass from the water – a material with a high refractive index – to the air – which has a lower index of fraction – it can only do so if its angle of incidence is smaller than the…
The Pythagorean Cup
According to legend, Pythagoras invented a cup to prevent his students from drinking too greedily. If they overfilled the cup, it would immediately drain out all the fluid. The trick works thanks to a U-shaped tube in the center of the cup. As long as the liquid level is below the highest point in the…
Shaking in the Wind
Sitting at a traffic stop on a windy day, you may have noticed the beam holding the traffic lights shaking steadily up and down. This phenomenon is called vortex-induced vibration. When the wind flows over the beam, it looks something like the flow animation shown above. Airflow follows the shape of the beam until near…
Fluid Fingers
Fluid phenomena can show up in unexpected places. The collage above shows patterns formed when an aluminum block is lifted during wet sanding, a polishing technique. The dendritic fingers are formed from oil and the slurry of sanded particles being polished away. They are an example of the Saffman-Taylor instability, which forms when less viscous…
Plesiosaur Swimming
Plesiosaurs are marine reptiles that thrived during the Jurassic period and went extinct some 66 million years ago. Since the first discoveries of plesiosaur fossils centuries ago, scientists have debated how the four-limbed creature would have swam. One approach to answering this question is to examine the efficiency of different strokes. Researchers have done this…