FYFD

Tag: solid mechanics

  • The Physics of Al Dente

    The Physics of Al Dente

    It’s a simple weeknight routine: toss a handful of spaghetti noodles in boiling water, wait a few minutes, and enjoy with the sauce of your choice. But there’s a surprising amount of physics in the humble strand of spaghetti, and a new model focuses on the way spaghetti sags and curls as it cooks.

    Spaghetti, like most pastas, is made of semolina flour mixed with water, extruded (in commercially produced spaghetti), and then dried. Once immersed in water, the rod of pasta begins to swell and soften as water works its way slowly inward. At the same time, it will lose some of its starches to the surrounding water. If the water is hot enough, the pasta undergoes an additional process, starch gelatinization, which is responsible for cooked pasta’s characteristic texture. That perfect al dente condition occurs right as the hydration front reaches the pasta’s core.

    As all of this happens, the initially straight spaghetti strand sags, settles, and curls. Researchers found that, even with a relatively simple model that assumes spaghetti doesn’t stick to the pot, they could capture shape change of individual spaghetti strands, suggesting it’s possible to identify perfectly cooked pasta by shape alone. (Image credit: Pixabay; research credit: N. Goldberg and O. O’Reilly; via Ars Technica)

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    Blooming Deposits

    Evaporate a droplet full of silica nanoparticles, and you’ll get beautiful, flower-like films. As the water evaporates, dry nanoparticles build up in a solid deposit. The evaporation creates a pressure gradient that pulls toward the center of the drop, forcing the deposit to bend. As stress builds in the deposit, cracks form petal-like segments. The number of cracks is indicative of how much of the drop was solid material; the higher the volume fraction of particles is, the fewer cracks form and the less the deposit bends. (Image, video, and research credit: P. Lilin et al.)

  • Inside Avalanches

    Inside Avalanches

    Avalanches have traditionally been difficult to model and predict because of their complex nature. In the case of a slab avalanche, the sort often triggered by a lone skier or hiker, there is a layer of dense, cohesive snow atop a layer of weaker, porous snow. The presence of the skier can destabilize that inner layer, causing a fracture known as an anticrack to propagate through the slab. Eventually, it collapses under the weight of the overlying snow and an avalanche occurs.

    What makes this so complicated is that the snow behaves as both a solid – during the initial fracturing – and as a fluid – during the flow of the avalanche. Researchers are making progress, though, using new models capable of simulating the full event (shown above) by leveraging techniques developed and used in computer animation for films. That’s right – the physics-based animation used in films like Frozen is helping researchers understand and predict actual avalanche physics! (Image and research credit: J. Gaume et al.; via Penn Engineering; submitted by Kam-Yung Soh)

  • Galapagos Week: Diving Birds

    Galapagos Week: Diving Birds

    One of my favorite things to do while we were sailing along the Galapagos was watching the blue-footed boobies hunt. Like the gannets shown above, boobies are plunge divers. They circle overhead until they spot their prey, then they fold their wings and dive headfirst into the water, impacting at speeds of more than 20 m/s (~45 mph). It’s absolutely incredible to watch. The physics involved are impressive, too, especially considering how badly a human would be injured diving at their speeds! 

    Fluid dynamically speaking, there are three important phases to the birds’ entry. The first is the impact phase, which lasts from initial contact until the bird’s head is underwater. In the second phase, an air cavity forms behind the head and around the neck as it enters the water. Finally, when the chest – the widest point of the bird – hits the water, the bird reaches the submerged phase. 

    Mechanically, the most interesting part is the air cavity phase. During this time, the bird’s head is slowing down due to high hydrodynamic drag from the water, but the rest of the bird is still moving fast. That means the bird’s slender neck experiences strong compressive forces, which would tend to make it buckle. Researchers at Virginia Tech examined this very problem and found that the birds’ sizing – its head shape, neck length, and so forth – combined with their typical diving speeds kept these birds well away from the conditions that would cause their necks to buckle. With the added stabilization from the birds’ neck muscles, they estimated that gannets and other plunge divers might be able to safely dive at speeds twice what would kill a human! Check out the BBC video below to see high-speed footage of gannets diving. (Image credits: G. Lecoeur; B. Chang et al.; research credits: B. Chang et al., pdf; video credit: BBC)

    Tomorrow will be the final day of Galapagos Week. Catch up on previous posts here.