We rarely consider just how complex the process is when we speak or sing. Sound waves produced in our larynx are shifted and amplified by the geometry of our throats, mouths, sinus cavities, tongues, and lips. This video provides a glimpse of that hidden complexity through a trained vocalist singing inside an MRI machine. He sings the same aria in four distinctly different vocal styles, and it’s incredible to watch all the changes his tongue, lips, and soft palette go through to produce those different sounds. (Image and video credit: T. Ross; via Flow Vis)
Rafts of sea ice follow swirling eddies in this satellite image of the Gulf of St. Lawrence. Just as with phytoplankton blooms and sediment, this thin sea ice can be moved by wind and currents to reveal hidden flow patterns. Experimentalists use many similar diagnostics that introduce bubbles, particles, smoke, and other tracers into flows to visualize motion that’s otherwise invisible. (Image credit: J. Stevens/NOAA/NASA; via NASA Earth Observatory)
When studying modern birds it quickly becomes apparent that they can either be good at swimming or at flying, but not at both. The characteristics that make wings good for flying are diametrically opposed to those that make for a good swimmer. So most species have chosen to invest in one strategy or the other. Penguin ancestors chose the swimming route tens of millions of years ago, in the aftermath of the extinction event that emptied our oceans of the large reptilian predators that had ruled them during the age of the dinosaurs. This video explores what we know about the fossil record of these birds, and it’s pretty incredible. Did you know there used to be 2-meter-tall penguins? (Image and video credit: PBS Eons)
Crisscrossing lines of wave clouds mark the wake of the Sandwich Islands in this satellite image. The tallest islands in the chain thrust rocky peaks more than 1000 meters above sea level, disrupting winds flowing across the ocean. Incoming air is forced up and over the mountain, which puts it at odds with the surrounding air at that height.
Due to differences in temperature and density, the disrupted air will continue to rise and sink periodically as it flows onward. At some heights it will cool enough to condense its water vapor into clouds, and at others, it will warm enough to lose any cloud cover. This is what creates the bands of clouds we see behind each individual island. (Image credit: L. Dauphin/NASA; via NASA Earth Observatory)
Tektites, like obsidian, are a naturally-occurring glass formed from molten rock. But tektites are often dumbbell or figure-8-shaped because they form in midair from spinning bits of fluid sent skyward after the crash of a meteor. In this video, Steve Mould takes us through the process and discusses some recent work by scientists who’ve created artificial tektites in the lab by levitating and spinning candle wax and other fluids. (Video and image credit: S. Mould; research credit: K. Baldwin et al.)
Anyone who’s used a can of compressed air to clean their computer or keyboard knows that the can quickly gets quite cold to the touch. This Minute Physics video explores some of the thermodynamics behind that process. Henry first identifies a few explanations that don’t quite line up with observations, before focusing in on the contents of the can: 1,1-difluoroethane. Inside the sealed can, this chemical sits in an equilibrium of part-liquid, part-vapor. But when pressure is released by opening the nozzle, the liquid boils, generating extra vapor and cooling whatever remains in the reservoir.
Although it’s not a good explanation for the compressed air can’s cooling, the cooling of an expanding gas is very important in applications like supersonic wind tunnels. That first equation you see at 0:36 in the video (for isentropic adiabatic expansion) is key to what happens in a nozzle with supersonic flow. As the flow accelerates to supersonic speeds, its temperature drops dramatically. When I was in graduate school, we actually had to preheat our hypersonic wind tunnel (in pretty much the same way you would preheat your oven at home) before we ran at Mach 6 because otherwise the temperature inside the test section would drop so low that the oxygen would liquefy out of the air! (Image and video credit: Minute Physics)
When glaciers form, they do so in layers, with clear blue ice sandwiched between sediment and air-bubble-filled white ice. Because each of these layers absorbs sunlight differently, they don’t melt evenly. The spikes and ridges seen in this ice formed because of this differential melting between layers. The blue ice is particularly good at absorbing visible wavelengths of light, and so erodes more easily than the other layers.
Although the results look somewhat similar to the penitente ice seen at high altitudes, the formation mechanisms are a little different. Penitentes rely heavily on sublimation — where their ice and snow change directly into a gas — rather than the melting seen here. That said, both eroded forms depend strongly on how different layers within them absorb and scatter sunlight. (Image credit: J. Van Gundy; via EPOD; submitted by Kam-Yung Soh)
Although we typically describe hydrophobic surfaces as “water-repelling,” we could just as easily focus on the fact that they’re “air-attracting.” This video from The Action Lab demonstrates that property nicely with a hydrophobic-coated “boat” that’s effectively unsinkable, thanks to its ability to trap air pockets.
Even punching holes through the boat doesn’t sink it because its surface is so chemically and physically attractive to air that the bubble won’t budge. In fact, as the video demonstrates, the only effective way to remove the hydrophobicity is to remove the air bubble by using a vacuum chamber. But even then, the effect only lasts until air is reintroduced to the boat. (Image and video credit: The Action Lab)
P.S. – No, this is not an April Fool’s joke, just actual science! – Nicole
Joe Hanson over at “It’s Okay to Be Smart” has a great video on the random walk photons have to make to escape the core of the sun and other stars. Because the high-energy photons born in the star’s core have to bounce their way out rather than flying in a straight line, those photons can spend thousands of years escaping the sun. After that, the eight-and-a-half minute trip to Earth is nothing.
But there’s a key element missing in this explanation: convection! That radiative random walk photons do doesn’t last all the way from the core of the sun to its surface. From a depth of about 200,000 km onward, the dominant mode of transport in the sun is convection, actual fluid motion that carries heat and light much faster than simple molecular diffusion, or Brownian motion, does. That’s why the surface of the sun shines with convection cells similar to the ones you’ll see in your skillet when heating a layer of oil.
Fluid motion beyond molecular diffusion is also a big part of the other flows Joe describes in the video. If you had to wait on Brownian motion in order to smell your morning coffee, it would be cold long before you knew it was there! (Video and image credit: It’s Okay to Be Smart; sun surface image credit: Big Bear Solar Observatory/NJIT)
Growing up, my summer nights often featured a chorus of crickets and bull frogs. Even now, the sound of those chirps reminds me of home. So how do crickets make their calls? As this video shows, it’s a matter of scraping the hard edge of one wing along a tiny series of spines, similar to the teeth of a comb, that sit on the other wing.
How fast the cricket’s wings move affects how frequently the chirps are heard. Being cold-blooded, the insects’ speed is affected by the external temperature, which is why you can count cricket chirps to estimate the temperature. Essentially, the chemical reactions necessary to regulate wing movement are temperature-dependent, so colder crickets produce slower chirps. (Video and image credit: Deep Look)
