FYFD

Tag: science

  • Galapagos Week: Lava Flows

    Galapagos Week: Lava Flows

    The Galapagos islands are geologically similar to the Hawaiian islands; both are archipelagos that were born and continue to be formed by lava flows originating from a volcanic hot spot. Lava from this type of volcano is high in basalt content, which affects both its flow properties and the formations it creates. Geologists have actually borrowed words from the Hawaiian language to describe the two main kinds of lava formations seen in basaltic flows: pahoehoe and a’a.

    Pahoehoe formations tend to be relatively smooth and often leave behind a pattern of rope-like coils (below). In contrast, a’a lava features are sharp, rough, and challenging to traverse. Both flows are gravity-driven, and which features a given eruption forms depends on many factors. Many flows will even begin with a pahoehoe section that stretches for several kilometers before transitioning to an a’a structure. Researchers believe the transition occurs when the lava crystallizes enough to develop a yield-strength, meaning that it will behave like a solid until enough force is applied to make it flow again. Toothpaste, ointment, and mud are similar so-called yield stress fluids which will only flow after a critical force is applied.  (Image credits: lava flow – Epic Lava Tours, source; pahoehoe lava – J. Shoer)

    Galapagos Week continues tomorrow here on FYFD. Check out previous posts.

  • Galapagos Week: Pistol Shrimp

    Galapagos Week: Pistol Shrimp

    One of the most striking things about snorkeling in the Galapagos was how loud it was underwater. There were hardly any boats nearby, but every time my ears dipped below the surface, I could hear a constant cacophony of sound. Some it came from waves against the sand, some of it was the sound of parrotfish nibbling on coral, but a lot of it was likely the work of a culprit I couldn’t see hidden in the sand: the pistol shrimp.

    These small crustaceans hunt with an oversized claw capable of snapping shut at around 100 kph. When the two halves of the claw come together, they push out a high-speed jet of water. High velocity means low pressure – a low enough pressure, in fact, to drop nearby water below its vapor pressure, causing bubbles to form and expand. These cavitation bubbles collapse quickly under the hydrostatic pressure of the surrounding water, creating a distinctive pop that makes the pistol shrimp one of the loudest sea creatures around. (Image credit: BBC Earth Unplugged, source; research credit: M. Versluis et al.)

    All week we’re celebrating the Galapagos Islands here on FYFD. Check out previous posts in the series here.

  • Galapagos Week: Marine Iguanas

    Galapagos Week: Marine Iguanas

    One of the most unique inhabitants of the Galapagos Islands is the marine iguana. These reptiles live in colonies of thousands and subsist entirely on marine algae. Smaller iguanas are intertidal feeders, grazing on green and red algae when it is exposed near low tide. But the largest iguanas feed near midday by swimming out and diving to feed on richer pastures. 

    The iguanas are surprisingly good swimmers, even though marine iguanas exhibit little extra specialization for it compared to other iguana species. They swim both at the surface and underwater with an undulatory motion driven by their tails. The iguana also streamlines its body somewhat by tucking its legs along its sides. Although the marine iguana is a much slower and less efficient swimmer than a bony fish of equal size, swimming is still a good choice for getting around. The marine iguana expends only 75% as much energy per distance swimming as it does walking. The big challenge is staying warm in the cold Galapagos waters. Small iguanas are both less efficient swimmers and lose body heat faster. This is why you’ll only see the biggest iguanas feeding underwater. (Image credits: N. Sharp; research credit: K. Trillmich and F. Trillmich; J. Videler and B. Nolet; G. Bartholomew)

    This is the first post of Galapagos Week here on FYFD. Check back every day for new Galapagos-themed posts!

  • Galapagos Week: Introduction

    Galapagos Week: Introduction

    One hundred and eighty-two years ago today, the H.M.S. Beagle reached the Galapagos archipelago carrying, among others, naturalist Charles Darwin. The ship would spend the next month exploring the islands, and Darwin’s experiences during that time, and the specimens he collected, would ultimately lead him to propose the concept of evolution.

    I had the incredible opportunity to visit the Galapagos Islands last October, and, like so many before me, I was fascinated by the islands and their remarkable ecosystems. The Galapagos Islands are located at the equator, but they owe much of their rich biodiversity to sitting at the confluence of several ocean currents, both warm and cold. In particular, the cold Cromwell Current’s upwelling on the western side of the archipelago carries valuable nutrients up from the deep and helps support vibrant marine life from bioluminescent plankton to leaping mobula rays. (And, yes, I geeked out over both.)

    Over the next week, FYFD will be exploring some of the fluid dynamics of the Galapagos Islands and their denizens on land, sea, and air. Be sure to check back every day for a new post! (Image credit: N. Sharp and J. Shoer)

  • Farewell, Cassini!

    Farewell, Cassini!

  • Featured Video Play Icon

    Lift Over Wings

    One of the most vexing topics for fluid dynamicists and their audiences is the subject of how wings generate lift. As discussed in the video above, there are a number of common but flawed explanations for this. Perhaps the most common one argues that the shape of the wing requires air moving over the top to move farther in the same amount of time, therefore moving faster. The flaw here, as my advisor used to say, is that there is no Conservation of Who-You-Were-Sitting-Next-To-When-You-Started. Nothing requires that air moving over the top and bottom of a wing meet up again. In fact, the air moving over the top of the wing outpaces air moving underneath it.

    In the Sixty Symbols video, the conclusion presented is that any complete explanation requires use of three conservation principles: mass, momentum, and energy. In essence, though, this is like saying that airplanes fly because the Navier-Stokes equations say they do. It’s not a terribly satisfying answer to someone uninterested in the mathematics.

    Part of the reason that so many explanations exist – here’s one the video didn’t touch on using circulation – is that no one has presented a simple, intuitive, and complete explanation. This is not to say that we don’t understand lift on fixed wings – we do! It’s just tough to simplify without oversimplifying.

    Here’s the bottom line, though: the shape of the wing forces air moving around it to change direction and move downward. By Newton’s 3rd law (equal and opposite reactions), that means the air pushes the wing up, thereby creating lift. (Video credit: Sixty Symbols)

  • Elastic Bounces

    Elastic Bounces

    A rigid ball accelerated by a moving surface can only ever move as fast as the surface propelling it. But that’s not true for squishy objects like a water droplet. The composite image above shows the trajectory of a water droplet launched from a moving superhydrophobic surface. As the surface starts rising, it squishes the droplet like a pancake, triggering a deformation cycle where the droplet will squish and extend repeatedly. How quickly the drop changes shape depends on factors like its size and surface tension. The researchers found that a droplet’s launch was strongly affected by the ratio of the droplet’s shape-changing frequency and the frequency of the plate’s motion. When the drop’s shape changed three times faster than the surface’s motion, it would catapult off the surface with 250% of the kinetic energy of a rigid ball!

    Launching elastic balls works the exact same way as droplets, indicating that the phenomenon depends on the way the projectiles deform. The process is similar to jumping on a trampoline. If a trampolinist times her jump just right, she’ll get more energy from the trampoline and fly higher. The droplet does the same when its deformation is properly tuned to its catapult. (Image credit: C. Raufaste et al.; via APS Physics; submitted by Kam-Yung Soh)

  • Flying Fish Aerodynamics

    Flying Fish Aerodynamics

    Flying fish, strange as it sounds, have aerodynamic prowess comparable to hawks. The fish aren’t true fliers, but they do glide for hundreds of meters using their large pectoral and pelvic fins as wings. Wind tunnel research shows the fish have their maximum lift at an angle of attack around 30-35 degrees, matching their typical take-off angle (top). Their best gliding performance occurs when they’re roughly parallel to the water (middle). The researchers even found that the fish use ground effect to enhance their lift. Although their aerodynamics allow flying fish to get out of reach of their aquatic predators, the fish must be wary of flying too high, as this makes them a target for frigatebirds (bottom). These acrobatic seabirds can’t get wet, but they have some impressive aerodynamics of their own to help make up for it.  (Image credit: BBC Earth, source; research credit: H. Park and H. Choi; see also SciAm)

  • Sunset Vortices

    Sunset Vortices

    Often our atmosphere’s transparency masks the beautiful flows around us. This spectacular image shows a flight landing in Munich just after sunrise. Low-hanging clouds get sliced by the airplane’s passage and curl into its wake. The swirls are a result of the plane’s wingtip vortices, which wrap from the high-pressure underside of the wing toward the low-pressure upperside. The vortices stretch behind in the plane’s wake, creating turbulence that can be dangerous to following planes. In fact, these vortices are a major determining factor in the frequency of take-off and landing on a given runway. The larger a plane, the larger its wingtip vortices and the more time it takes for the turbulence of its passage to dissipate to a safe level for the next aircraft. (Image credit: T. Harsch; submitted by Larry S.)

  • Jupiter On Display

    Jupiter On Display

    The rich detail of Jupiter’s atmosphere is on full display in this enhanced-color image from the Juno spacecraft. (Full resolution version here – trust me, you want to click that link.) To the north, on the left side of the image, Jupiter’s Great Red Spot swirls. To the center and right, the cloud bands of Jupiter’s southern region are coming into view. The color enhancements really highlight eddies on the edge of these bands. These are examples of Kelvin-Helmholtz instabilities caused by shear between cloud bands moving at different speeds. Within the bands, smaller vortices spin. Some of these are anti-cyclones, high-pressure storm systems found all over the planet. Jupiter’s atmosphere still holds many mysteries for scientists, but I love how every gorgeous image Juno sends back shows fluid physics written larger than life across our solar system’s biggest planet. (Image credit: NASA/JPL-Caltech/SwRI/MSSS/G. Eichstädt /S. Doran; via Gizmodo)