Tag: fluid dynamics

Squishy Actuators
Hard materials don’t always work well in robotics. Here, researchers build soft actuators that can bend, curl, and tighten in order to manipulate objects. They begin by injecting liquid elastomer into a tube (Image 1), followed by a bubble of air. Buoyancy makes the air bubble rise within the tube, creating an asymmetric cross-section where the solidified elastomer has a thin shell along one side and a thicker wall along the other (Image 2). When high-pressure air is pumped into the soft tubes, their asymmetric cross-section makes them bend and twist (Image 3). The team found that they can tune the elastomer tubes to form complex shapes good for gripping and flexing — perfect for a soft robot! (Video and image credit: T. Jones et al.; research credit: T. Jones et al.)
May 5, 2022
Re-Entry For X-Wings
Fans of sci-fi and fantasy have a long-standing tradition of exploring the physics and/or practicality of creations in their fandom, and Star Wars fans are no exception. Here engineers ask whether Luke Skywalker’s X-wing fighter could survive the descent through Dagobah’s atmosphere as he searched for Master Yoda. Their results are based on a numerical simulation, with some assumptions about the spacecraft’s descent path and design as well as the planet’s atmosphere. Fans of the Jedi will be glad to hear that the X-wing can survive its supersonic descent intact, delivering the last Jedi safely to his mentor. (Image credit: Y. Ling et al.)
May 4, 2022
Ant Bridge
As red ants scout their way to food, the terrain can sometimes get in the way. Here a leading scout has made their body into a bridge that their fellows can use to cross the watery gap. Take a close look at the water’s surface and you’ll see that the meniscus curves up to meet the rocks. That’s a clue that this image is really very small! For water on Earth, that curvature only occurs at lengths below a couple of millimeters, where surface tension has the power to overcome gravity’s efforts to flatten the surface. The ants’ bridge is only possible because the red ant is small enough and light enough for surface tension to support it. Learn more about the amazing interactions of ants and water in some of my previous posts. (Image credit: Chin Leong Teo; via Colossal)
May 3, 2022
Box Closing Physics
My fellow board game aficionados (and anyone else who regularly opens and closes lidded boxes) have probably noticed the way a lid drops slowly onto its box once aligned. The weight of the lid pressurizes air inside the box, driving a flow through the narrow gap between the walls of the box and the lid. Researchers found that the time it takes for a box to slide closed is closely related to the size and shape of the gap between the walls. Despite gaps of less than 1 millimeter, air moving out of the box typically flows at about 1 meter per second!
With their mathematical model of the flow from a closing box, the group was also able to determine the optimal shape for a fast-closing box, something that may be of interest to manufacturers as well as fans of board games. (Image credit: N. Sharp; research credit: J. de Ruiter et al.; via APS Physics)
May 2, 2022
“ColorLover”
“ColorLover,” a short film by artist Rus Khasanov, is a delightful liquid rainbow. The video’s ingredients seem to be ink, paint, oil, and a bit of superhydrophobic coating primed to reveal a heart. I love that latter touch; it’s a cool way to use regular materials in a way that some might assume involved digital effects! (Video credit: R. Khasanov)
April 29, 2022
Explaining the Roaming Rocks
For nearly a century, the long meandering tracks etched into Death Valley’s Racetrack Playa remained a mystery. Clearly, some force was pushing the heavy rocks there and leaving behind these grooves. But with the remoteness of the location, it took investigators years to catch the rocks in action and solve the puzzle. For those who haven’t watched the video yet, I’ll refrain from revealing the answer here (though you can find it in previous FYFD entries)! I’ll just say that it requires all the right conditions to come together. (Image and video credit: Physics Girl; for related research see here)
April 28, 2022
Making Yeast-Free Pizza
Yeast is a key ingredient in many pizza doughs; as the yeast ferment sugars in the dough, they produce carbon dioxide which bubbles into the dough, creating the light and airy texture necessary for a good crust. It’s a slow process, though, often requiring several hours for the dough to rise. Recently, researchers studied an alternative pizza-making method that generates bubbles in the dough via pressurization — with no yeast required.
The new technique is similar to the process used to carbonate sodas. The team mixed flour, water, and salt and placed the dough in an autoclave, which allowed them to control both temperature and pressure during baking. They dissolved gas into the dough at high pressure and then carefully released the pressure during baking, allowing the bubbles to grow. They used rheological measurements to compare the characteristics of yeasted and yeast-free doughs at various stages in the leavening and baking processes.
Now that they have the methodology down, they’ve purchased a food-grade autoclave and are looking forward to taste testing their yeast-free creations — none more so than their team member who has a yeast allergy! Since the pressures required for their method are quite mild, they hope it’s a technique that restaurants will take on. (Image credit: B. Huff; research credit: P. Avallone et al.)
April 27, 2022
Teaching Diffusion With Eggs
Many cultures around the world marinate hard-boiled eggs — like pickled eggs in Europe or tea- and soy-infused eggs from Asia. These delicacies offer a fun (and tasty) way to demonstrate the concept of diffusion, the tendency of a substance to move from areas of high concentration to low concentration via random molecular motion.
Simply steep peeled, hard-boiled eggs in your sauce (or food dye) of choice. Remove an egg every so often and slice it in half to see how far the sauce traveled. You can also play with the temperature to accelerate the diffusion. The longer an egg steeps and the hotter its surroundings, the further into the egg white the sauce will diffuse! (Image credit: Wordridden; research credit: C. Emeigh et al.)
April 26, 2022
Dispelling Ice
In winter weather, delays pile up at airports when planes need de-icing. Our current process involves spraying thousands of gallons of chemicals on planes, but these chemicals are easily removed by shear stress and dissolution, meaning that by the time a plane takes off, there is little to no de-icing agent remaining on the plane. Instead, those chemicals become run-off.
Researchers looking to change that have developed a family of anti-icing coatings — including creams, sprays, and gels — that are easy to use and apply, non-toxic, and much longer lasting than conventional methods. Ice slides easily off their gel coatings, which remain optically transparent even under freezing conditions — and ice can take 25 times longer to form on the gels compared to current anti-icing tech.
The team envisions using their coatings on much more than airplanes. Imagine traffic lights that can’t be obscured by ice or snow, a windshield on your car that never freezes over, or even an anti-icing spray that could protect crops from a sudden freeze! (Image, video, research, and submission credit: R. Chatterjee et al.; see also)

April 25, 2022
“Reverent”
Today, enjoy this moody black-and-white short film of storm timelapses. Photographer Mike Olbinski is a master of this subject. I never tire of watching his towering convective supercell thunderstorms or his picturesque microbursts. The lightning-lit clouds in the latter half of the film are particularly spectacular (assuming you do not have sensitivities to flashing lights). And there are a few haboobs and a tornado in there for good measure, too. (Image and video credit: M. Olbinski)
April 22, 2022