When a butterfly emerges from its chrysalis, it flaps its wings to help pump fluids through its body, essentially inflating its new adult form. You get a glimpse of that process here in this Ant Lab video, along with some spectacular slow motion footage of butterflies taking off. I’m always amazed to see how much butterfly wings flex with each wing beat! Even more impressive is the strength of the insect’s lift; as seen here, a butterfly is strong enough to take off while supporting both itself and a mated insect. (Image and video credit: Ant Lab/A. Smith)
Tag: science
Stopping The Drop
When a droplet falls on a mesh surface, some of the liquid can burst through the holes (top row). But subsequent drops have a harder time penetrating the prewetted mesh. After a few drops have impacted (rows 2-3), the wetted mesh can completely suppress penetration (rows 4-5). The authors found that the taller drops sitting atop the mesh were better at stopping penetration from an incoming drop. (Image and research credit: L. Xu et al.)
Streaks of Sea Ice
As summer approaches in the Southern Ocean, sea ice melts, but the process is not purely one-way. Temperatures in some locations are cold enough for some limited new freezing. The result is a mix of ice conditions like those seen here. The oldest, thickest ice is part of the ice shelf in the image’s lower right. Normally, younger sea ice would nestle against this shelf, but strong winds have blown that ice north-eastward.
In the open waters between, delicate frazil ice — tiny needle-like crystals — forms. The wind, coupled with the wave motion, drives the frazil ice together to form streaks of nilas, which eventually accumulate into a layer along the older, broken, windswept ice. (Image credit: J. Stevens/USGS; via NASA Earth Observatory)
Sounds of Champagne
Lean in to a glass of champagne and you’ll hear a soft chorus of sound as the bubbles pop. Recently, researchers determined the specific mechanism in the process that’s responsible for that audible sound.
Bubbles pop when the thin film of liquid separating them from the atmosphere drains away. The moment the film opens corresponds to the start of the sound, as overpressurized air inside the bubble has a chance to escape. The researchers found that the bubble behaves like a open-ended Helmholtz resonator, and by the time the sound emission ends, the bubble’s collapse has barely begun. (Image credit: L. Lyshøj; research credit: M. Poujol et al.)
Beijing 2022: Sliding on Snow
Skiing and snowboarding events rely on the peculiar physics of sliding on snow. According to classical lubrication theory, that sliding shouldn’t be nearly as low in friction as what we observe. The key here is that snow is soft and porous; it’s compressible, but it can also trap air (or water) in the pores between flakes. Because the passage of a skier or snowboarder is so fast, the air doesn’t have the time to slip out of the pores. Instead, it gets pressurized, providing lift that keeps the slider’s friction low. In the end, it isn’t the snow holding the slider up, it’s the air trapped in the snow beneath them! (Image credit: skier in powder – J. Andersson, snowboarder – Visit Almaty, halfpipe – P. T’Kindt; research credit: Z. Zhu et al.)
Beijing 2022: Ice’s Slideability
As scientists continue to unravel the peculiarities of ice, they’ve found that ice’s friction depends both on the object sliding on it and the ice’s hardness. At extremely low temperatures, water molecules at the ice’s surface are held rigidly by the hard ice, resulting in high friction. At intermediate temperatures, however, water molecules at the surface were more mobile — especially with a quick-moving slider going by — so the friction decreased.
But as the ice approached its melting point, the friction behavior shifted again. As the ice softened, sliding objects could begin to plough into the ice, dramatically increasing contact and friction. When ploughing begins depends on temperature, slider shape, contact pressure, slider speed, and ice hardness.
Beyond the lab, researchers found that weather plays a role in slideability, too, since humidity and air temperature can affect the thickness of the liquid-layer at the ice’s surface. (Image credit: SHVETS Productions; research credit: R. Liefferink et al.; via APS Physics; submitted by Kam-Yung Soh)
Beijing 2022: Monobob
Bobsleigh, as a discipline, has been dominated in recent years by teams seeking every aerodynamic advantage to shave hundredths of a second off their runs. So it’s fascinating that the newest event in the discipline — the women-only monobob — cuts away that secretive part of the sport by permitting sleds from only one manufacturer. Every athlete competes in an identical sled. Not only that, they swap sleds between runs based on their times! So the fastest athlete from the first run will switch sleds with whomever had the slowest time.
The event’s rules refocus the competition on athletic performance and skill rather than incentivizing countries who can afford to spend more money on wind tunnel testing and F1 design companies. That’s a great step toward leveling the playing field. I can’t wait to watch! (Image credit: OIS)
Beijing 2022: Ski Jumping
In ski jumping, aerodynamics are paramount. Each jump consists of four segments: the in-run, take-off, flight, and landing. Of these, aerodynamics dominates in the in-run — where jumpers streamline themselves to minimize drag and maximize their take-off speed — and in flight. During flight, ski jumpers spread their skis in a V-shape and lift their arms to the sides to turn themselves into a glider. Their goal is to maximize their lift-to-drag ratio, so that the air keeps them aloft as long as possible. Because of the short flight time and high risk of taking jump after jump, many elite ski jumpers use wind tunnel time to practice and hone their flight positioning, as seen in the video below.
Weather also plays a significant role in ski jumping; it’s one of the few sports where a headwind is an advantage to athletes. To try to adjust for wind effects, scoring for the sport uses a wind factor. (Image credit: T. Trapani; video credit: NBC News)
Beijing 2022: Why Are Ice and Snow Slippery?
Although every Olympic winter sport relies on the slippery nature of snow and ice, exactly why those substances are so slippery has been an enduring mystery. Michael Faraday hypothesized in the nineteenth century that ice may have a thin, liquid-like layer at its surface, something that modern studies have repeatedly found.
One recent study used an entirely new instrument to probe the characteristics of this lubrication layer and found that it is only a few hundred nanometers thick. But the fluid in this layer is nothing like the water we’re used to. Instead it has a viscosity more akin to oil and its response to deformation is shear-thinning and viscoelastic, more like the complex fluids in our kitchens and bodies than pure, simple water. They found that using a hydrophobic probe modified the interfacial viscosity even further, which finally provides a hint at the mechanism behind waxing skis and skates.
Fortunately for us, we’ve found plenty of ways to employ and enjoy water’s slipperiness, even as the mystery of it slowly gives way to understanding. (Image credit: M. Fournier; research credit: L. Canale et al.; via Physics World; submitted by Kam-Yung Soh)
Luminous Fruits
Light shines through citrus and melon in this
photographicphotorealistic series of paintings from artist Dennis Wojtkiewicz. The strong illumination reveals the underlying structure of pith, pulp, and juice. The deformable pockets of fluid in the peel of citrus fruits are the source of some incredible microjets. When the peel bends, it compresses these tiny fluid-filled pockets, creating incredibly high pressures that eventually drive a burst of oil at g-forces comparable to those felt by a bullet fired from a gun. Learn more about citrus jets here and see more of Wojtkiewicz’s work and purchase prints here on his site. (Image credit: D. Wojtkiewicz; via Colossal)ETA: Thanks to A.J. for pointing out that Wojtkiewicz is, in fact, a painter (and not a photographer), making his work all the more astounding! We regret the error.
