Seven waterspouts align as lava from the Hawaiian volcano Kilauea pours into the ocean in this striking photo from photographer Bruce Omori. Like many waterspouts–and their landbound cousins dust devils–these vortices are driven by variations in temperature and moisture content. Near the ocean surface, air and water vapor heated by the lava create a warm, moist layer beneath cooler, dry air. As the warm air rises, other air is drawn in by the low pressure left behind. Any residual vorticity in the incoming air gets magnified by conservation of angular momentum, like a spinning ice skater pulling her arms in. This creates the vortices, which are made visible by entrained steam and/or moisture condensing from the rising air. (Photo credit: B. Omori, via HPOTD; submitted by jshoer)
Tag: physics
Top 10 FYFD Posts of 2014
It’s only fitting to take a moment to look back at 2014 as we step into the New Year. It was a big year in many respects – we hit 1000 posts and broke 200,000 followers; I started producing FYFD videos on our YouTube channel; and, on a personal note, I finished up my PhD. But since we’re all about the science around here, I will give you, without further ado, the top 10 FYFD posts of 2014:
1. Bioluminescent crustaceans use light for defense
2. What happens when you step on lava
3. Flapping flight deconstructed
4. Wingtip vortices demonstrated
5. Saturn’s auroras
6. Raindrops’ impact on sand
7. Water spheres in microgravity
8. The surreal undulatus asperatus cloud
9. Inside a plunging breaker
10. A simply DIY Marangoni effect demoI can’t help but notice that 9 out of the 10 posts feature animated GIFs. Oh, Tumblr, you rascals. Happy New Year! (Image credits: BBC; A. Rivest; E. Lutz; Nat. Geo/BBC2; ESA/Hubble; R. Zhao et al.; D. Petit; A. Schueth; B. Kueny and J. Florence; Flow Visualization at UC Boulder)
A Toast!
When you lift a glass of champagne or sparkling wine at midnight tonight, your nose and mouth will be greeted by a plethora of aromas, flavors, and sensations propagated by the tiny bubbles in the drink. Carbon dioxide dissolved in the wine gathers in a stream of tiny bubbles that rise at the center of the glass. (The bubbles form at the center because champagne glasses are often etched in a ring there to provide nucleation points where the bubbles can grow.) This stream of rising bubbles generates vortical motion in the glass that helps carry the carbon dioxide to the surface, where it is released when the bubbles burst. In the tall, thin champagne flute these vortices mix the entire contents of the glass, but, in a wider coupe, the vortices are confined to the center, leaving a stiller region along the glass’s edges. For those who find that a freshly poured flute of champagne stings their noses–a side effect of the high gaseous carbon dioxide concentration just after decanting–the wider coupe lowers the concentration at the glass’s lip and may provide a more pleasant experience for toasting the new year. (Image credit: F. Beaumont et al.)
Grow Your Own Snowflakes
If your Christmas holiday was a little too green (like mine was), Science Friday has just the activity for you – grow your own snowflakes! With a few materials you probably already have and some dry ice from the store, you can grow and observe ice crystals at home. Although these crystals form from water vapor instead of water droplets like proper snowflakes, they do exhibit different structures depending on temperature and humidity, just the way natural snowflakes do. (Video credit: Science Friday/F. Lichtman)
Manipulating Fluids
Combining water-repelling superhydrophobic surfaces with water-loving hydrophilic surfaces allows scientists and engineers to manipulate common fluids. Here a hydrophilic track surrounded by a superhydrophobic background collects and distributes drops of dyed water. The wetting characteristics of the surface combined with surface tension in the liquid drives the flow. No pumping or power input is necessary. This kind of manipulation of droplets can be especially useful in biomedical applications where fast-acting, low-cost devices could be used to diagnose diseases or measure blood glucose levels. (Image credit: A. Ghosh et al., via NSF; see also source video)
Splashy Heroines
In his latest work, photographer Jaroslav Wieczorkiewicz used splashing liquids to create fantastical superheroine costumes. The splashes are all real, composited together in post-production from hundreds of individual splashes. He uses cold whole milk as his base liquid, sometimes supplementing with dye or paint for color. There’s also a behind-the-scenes video showing how the pictures are made, but, fair warning, it’s in German with some English subtitles and does contain nudity (link). (Image credits: J. Wieczorkiewicz; via Gizmodo)
Growing Snowflakes
It’s easy to miss the beauty of a snowflake if you don’t take a close look. These tiny crystals form when water freezes onto a dust particle or other nucleation site, and they grow as water vapor freezes on to the nucleus. The structured appearance of a snowflake comes from the bonds formed between water molecules, but the exact type and shape of crystal formed–not all snowflakes are six-sided!–depends on the local temperature and humidity during freezing. This microscopic timelapse video by Vyacheslav Ivanov lets you watch the process in action. (Video credit: V. Ivanov; via io9)
Viscous Droplet Impacts
Viscosity can have a notable effect on droplet impacts. This poster demonstrates with snapshots from three droplet impacts. The blue drops are dyed water, and the red ones are a more viscous water-glycerol mixture. When the two water droplets impact, a skirt forms between them, then spreads outward into a sheet with a thicker, uneven rim before retracting. The second row shows a water droplet impacting a water-glycerol droplet. The less viscous water droplet deforms faster, wrapping around and mixing into the other drop before rebounding in a jet. The last row switches the impacts, with the more viscous drop falling onto the water. As in the previous case, the water deforms faster than the water-glycerol. The two mix during spreading and rebound slower. In the last timestep shown, the droplet is still contracting, but it does rebound as a jet thereafter. (Image credit: T. Fanning et al.)
“Marco Polo” Theme
Netflix’s new original series “Marco Polo” has a distinctive and fluidsy title sequence. The artistic team at the Mill created the effect by painting images in water atop dense paper before introducing Japanese sumi-ink. Using high-speed photography, they filmed the diffusion of the ink into the water as it reveals the larger picture. There’s a great behind-the-scenes break down and video over at their blog. (Video credit: The Mill, submitted by jshoer)
Propagating Flames
Like many flows, flames can be unstable and undergo a transition from orderly laminar flow to chaotic turbulent flow. The timelapse image above shows the propagation of a flame front travelling downward. Each blue line represents the forwardmost position of the flame at a specific time. The flame is essentially two-dimensional, held between two glass plates separated by a 5-mm gap. The V-like points in the flame front are called cusps, and if you look closely, you can see cusps forming and even merging as the flame moves downward. Also notice how the flame front is more uniform near the top of the image, but, by the bottom, it has split into many more cusps. This is one of the indications that the flame is unstable. Check out the full poster-version of the image in the Gallery of Fluid Motion. (Photo credit: C. Almarcha et al., original poster)
