FYFD

Tag: surface tension

  • Sea Foam

    Sea Foam

    Photographer Lloyd Meudell captures surrealistic images of breaking sea foam.

    Interestingly, the sea foam is essentially a three-phase fluid made up of air, water, and sand. Yet despite the surrealism of its forms, the foam bears strong resemblance to other flows. The shapes the foam forms are reminiscent of vibrated non-Newtonian fluids like paint or oobleck. Momentum deforms the foam into sheets and ligaments smoothed and held together by surface tension until droplets snap free. You can find more of Meudell’s work at his site. (Image credits: L. Meudell; via freakingmindblowing; submitted by molecular-freedom)

  • Get Your Own Space Coffee Cup

    Get Your Own Space Coffee Cup

    A few weeks ago, we reported on the espresso machine NASA and the ESA sent to astronauts aboard ISS. The Capillary Beverage Experiment, known colloquially as the “Space Coffee Cup”, is an accompanying project that aims to use our understanding of fluid behavior in microgravity to design an open cup that simulates earthbound drinking experiences. As you can see above, astronauts are already enjoying drinks with it. The cup’s special shape is optimized so that surface tension can replace the role gravity plays in drinking on Earth. Where we pour drinks on Earth, the cup wicks liquid to the spout using surface-tension-driven capillary action. Right now there are only a handful of 3D printed cups on-orbit and here on Earth, but the company that designed them wants to manufacture glass versions for use here on the ground. So if you’d like your own space coffee cup, be sure to check out their Kickstarter campaign! (Video credit: IRPI LLC; image credit: NASA/IRPI LLC; Kickstarter project link)

    ETA: To those who have been asking, that’s European astronaut Samantha Cristoforetti, who is (clearly) a Star Trek fan. I believe she’s doing a tribute to Captain Janeway’s coffee. (Black.)

  • Featured Video Play Icon

    Acoustic Levitation

    Destin from Smarter Every Day has a great new video exploring acoustic levitation. With carefully placed speakers, you can create a standing wave with sound that’s capable of levitating lightweight objects against the force of gravity. Around 4:00, Destin demonstrates this with colored water droplets, which is where the real fireworks start. As he turns up the volume on the speakers, the big droplets explode. This happens when surface tension can no longer hold the drop together. But the high-speed footage offers other clues about what’s going on. Notice how the drops flatten out as the sound volume increases. If you look back to the standing wave animation at 1:33, you’ll notice that just to either side of the nodes (the spots that don’t move), the wave is still oscillating back and forth a little bit. As you increase the sound volume, that standing wave gets stretched to a larger amplitude, which means that those little oscillations just to either side of the node get stronger (and steeper), too. This change in acoustic pressure squishes the drops into pancakes as the fluid tries to stay right at the node. Eventually the droplet is just too flattened for surface tension to keep it together and it bursts into smaller droplets. (Video credit: Smarter Every Day; submitted by Matthew P.)

  • Featured Video Play Icon

    Make Your Own Dancing Droplets

    As a follow-up to last week’s “dancing droplet” post, here’s a video that describes how to recreate the experiment yourself at home. The droplet motion is driven by the two-component structure of the droplets, where differing evaporation rates and surface tension values between the two fluids in the drop cause the attractions and chasing behavior you see. To demonstrate this at home, you’ll need glass, fire (for sterilization), tweezers, a pipette, water, and food coloring. Looks like a fun way to spend a weekend afternoon! (Video credit: M. Prakash et al.; via io9)

  • Rowing Water Striders

    Rowing Water Striders

    Water strider insects are light enough that their weight can be supported by surface tension. For some time, they were thought to propel themselves by using their long middle legs to generate capillary waves–ripples– that pushed them forward, but juvenile water striders are too small for this technique to work. Instead researchers found that water striders move by using their middle legs like oars. The leg motion creates vortices about 4 mm below the water surface, and this water moving backward propels the insect forward. In the photos above, the scientists visualized the flow by sprinkling thymol blue on the water and letting the striders move freely. You can learn more about the work here or in this Science Friday episode. (Photo credits: J. Bush et al.)

  • Dancing Droplets

    Dancing Droplets

    What makes drops of food coloring able to dance, chase, sort themselves, or align with one another? This unexpected behavior is a consequence of food coloring consisting of two mixed liquids: water and propylene glycol. Both have their own surface tension properties and evaporation rates, which ultimately drives the behavior you see in the animations above. Both long-range and short-range interactions are observed. The former are due to vapor from each droplet adsorbing onto the glass around the droplet, thereby changing the local surface tension and causing nearby drops to feel an attractive force. The short-range effects are also surface-tension-driven. Droplets with lower surface tension will naturally try to flow toward areas of higher surface tension, which causes them to “chase” dissimilar adjacent drops. You can learn more about the research in the videos linked below (especially the last two), or you can read about the work in this article or the original research paper. (Image credit: N. Cira et al., source videos 1, 2, 3, 4; GIFs via freshphotons; submitted by entropy-perturbation)

  • Manipulating Fluids

    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)

  • Featured Video Play Icon

    Raindrops on Sand

    Here is a high-speed look at the impact of a raindrop on a sandy beach. In this case, a water droplet is falling on a bed of uniform glass beads, but the situation is effectively the same. Depending on the speed of the drop at impact, many types of craters are possible. The higher the impact velocity, the greater the momentum of the drop at impact and the more likely the drop is to tear apart when surface tension can no longer hold it together. Interestingly, there is remarkable similarity between the shape and behavior of these liquid drop impacts and those of a catastrophic asteroid impact. (Video credit: R. Zhao et al.)

  • Piazza del Popolo

    Piazza del Popolo

    The lions of the fountain in Rome’s Piazza del Popolo eject a turbulent sheet of water. Random fluctuations in the water sheet cause holes to form. Driven by surface tension, these holes grow and merge, leaving behind ligaments of water which quickly break up into a spray of unevenly-sized drops. (Image credit: E. Villermaux)

  • Coalescence in Microgravity

    Click through to see.

    Microgravity is a wonderful playground for fluid dynamics. Here astronaut Reid Wiseman demonstrates the interplay of forces involved in coalescence. When smaller droplets hit with insufficient force, they bounce off the water sphere. But if they hit hard enough to overcome surface tension, they coalesce with the sphere. I think the space station needs a high-speed video camera; I’d like to see this behavior at a few thousand frames per second! (Video credit: R. Wiseman/NASA)