Shovel-nosed snakes and sandfish lizards both swim through granular materials like sand. Researchers at Georgia Tech used x-rays to observe their subsurface motions. Despite their different shapes, the long, slender snake and the shorter, wider lizard both move under the sand by projecting traveling waves along their bodies. The snake’s long, skinny body allows it to have more bends along its length, which increases its transport efficiency because it allows the snake to move mostly through the tunnel created by its head’s passage. In contrast, the sandfish’s motions fluidize the sand around it, enabling it to swim. Although the snake is faster, both animals have optimized their motions for fast, low-energy transit according to their body type. (Video credit: Georgia Tech; research credit: S. Sharpe et al.; via io9)
Tag: biology
Filter-Feeding
Sponges are filter-feeding marine animals that rely on water flow to obtain their nutrients and remove waste. By injecting non-toxic fluorescein dye at their base, one can visualize the flow they induce in the water. Only seconds after the dye is introduced, the sponges have pumped it in, through, and out. Different parts of the sponge filter particles of various sizes for food. Oxygen and carbon dioxide are transported, respectively, into and out of cells via diffusion. In this way, the sponge’s pumping fulfills digestive, respiratory, and excretory functions. (Image credit: Jonathan Bird’s Blue World, source video; submitted by Jason C)
Colonial Life
Hydroids are small underwater animals that often live in colonies made up of individual polyps. The colony is interconnected through the gastrovascular system, which is responsible for both digestion and respiration. In the images above, a single polyp in the colony has been fed food dyed with a fluorescent tracer. The polyp serves as a circulating pump and, as the food is digested and the tracer released, more and more of the colony becomes visible. Watch the full video and read more about the experiment. (Video credit and submission: L. Buss Lab)
The Physics of Sneezing
Sneezing can be a major factor in the spread of some illnesses. Not only does sneezing spew out a cloud of tiny pathogen-bearing droplets, but it also releases a warm, moist jet of air. Flows like this that combine both liquid and gas phases are called multiphase flows, and they can be a challenge to study because of the interactions between the phases. For example, the buoyancy of the air jet helps keep smaller droplets aloft, allowing them to travel further or even get picked up and spread by environmental systems. Researchers hope that studying the fluid dynamics and mathematics of these turbulent multiphase clouds will help predict and control the spread of pathogens. Check out the Bourouiba research group for more. (Video credit: Science Friday)
Bioluminescence
In the dark of the ocean, some animals have evolved to use bioluminescence as a defense. In the animation above, an ostracod, one of the tiny crustaceans seen flitting near the top of the tank, has just been swallowed by a cardinal fish. When threatened, the ostracod ejects two chemicals, luciferin and luciferase, which, when combined, emit light. Because the glow would draw undesirable attention to the cardinal fish, it spits out the ostracod and the glowing liquid and flees. Check out the full video clip over at BBC News. Other crustaceans, including several species of shrimp, also spit out bioluminescent fluids defensively. (Image credit: BBC, source video; via @amyleerobinson)
The Churning of Corals
Corals may appear static, but near the surface the tiny hair-like cilia of these polyps are churning the water. Although it has been known for some time that corals have cilia, scientists had previously assumed they only moved water parallel to the coral’s surface. Instead recent flow visualizations show that the cilia’s movements generate larger-scale vortical flows near the coral that can help draw fresh nutrients in as well as flush waste away. This means that, instead of being reliant on currents and tides, corals can exert some control on their environment in order to get what they need. This insight into coral cilia may shed some light on the micro- and macroscopic flows generated by other cilia, like those in our lungs. For a similar example of seemingly-passive organisms generating their own flows, check out how mushrooms create air currents to spread their spores. (Image credits: O. Shapiro et al. and MIT News; source video; h/t to Katie B)
Seahorse Hunting
Those who have observed the languid pace of seahorses or seadragons swimming might think these fish only hunt slow prey. In fact, the tiny crustaceans on which they feed are extremely quick, capable of velocities over 500 body lengths per second. Instead of speed, the seahorse relies on stealth to capture its prey, as shown in the holographic video above. Seahorses use a pivot method to feed, simultaneously shifting their snouts up and sucking water in to catch their target. But this method of feeding only works for distances of about 1 mm. To get that close in the first place, the seahorse must approach its prey without alerting it. Researchers found that both the seahorse’s head shape and its natural posture create a hydrodynamic quiet zone just off the seahorse’s snout, directly in its strike zone. Fluid velocity and deformation rates in this region are significantly lower than those around the rest of the seahorse’s face when it moves, allowing the fish to sneak up on its prey. These adaptations are remarkably effective, too; the researchers observed that the seahorses were able to position themselves within 1mm of their prey without alerting them 84% of the time. (Video credit: B. Gemmell et al.; via Discover)
Sharkskin Fluid Dynamics
Sharks have evolved some incredible fluid dynamical abilities. Instead of scales, their skin is covered in microscopic structures called denticles. To give you a sense of size, each denticle in the black and white image above is about 100 microns across. Denticles are asymmetric and overlap one another, creating a preferential flow direction along the shark. When water tries to move opposite the preferred direction, the denticles will bristle, like in the animation above. The bristled denticles form an obstacle for the reversed flow without any effort on the shark’s part. Since local flow reversal is an early sign of separation, researchers theorize that this bristling tendency prevents flow along the shark’s skin from separating. Keeping flow attached, especially along the shark’s tail, is vital not only to the shark’s agility but to keeping its drag low. Researchers have even begun 3D printing artificial shark skin to try and harness the animal’s hydrodynamic prowess. For much more shark-themed science, be sure to check out this week’s “Several Consecutive Calendar Days Dedicated to Predatory Cartilaginous Fishes” video series by SciShow, It’s Okay to be Smart, The Brain Scoop, Smarter Every Day, and Minute Physics. (Image credits: J. Oeffner and G. Lauder; A. Lang et al.; original video; jidanchaomian)
Why Do Joints Pop?
Joint popping is one of those things some people revel in and others detest. What you may not have realized, though, is that fluid dynamics are responsible for the sound. Joints contain a non-Newtonian liquid called synovial fluid to lubricate them. When you manipulate the joint to stretch it, pressure in the fluid drops and gases dissolved in the synovial fluid are released, forming a cavitation bubble. The creation and collapse of this bubble are what cause the audible popping. (Video credit: SciShow)
Catching Prey
Over at Smarter Every Day, Destin has a new video, this time about how fish eat, which involves some pretty awesome physics. Instead of accelerating their entire body to close the distance to prey, fish thrust their jaws forward. As they do, they open their mouth, expanding the volume there and lowering the pressure. This causes water to flow into their mouth, pulling the prey with it. But the water has momentum, which would push the fish backward. To prevent this, the fish then opens its gills, allowing the water to rush back out while trapping the prey in its mouth. Be sure to check out Destin’s video so that you can see the process in high-speed. (Video credit: Smarter Every Day)
