Tag: science

This Is Your Brain
The human brain, like an egg, consists of soft matter bathed in a fluid and encased in a hard shell. To better understand how our brains respond to sudden accelerations, researchers looked at how egg yolks behave. In a purely translational impact (Image 1), the egg yolk deforms very little. But rotational motions (Images 2 and 3) cause major effects because of the imbalance between pressure forces outside the yolk’s membrane and the centrifugal forces within it. Rotational deceleration was particularly potent (Image 3).
The researchers’ findings are consistent with concussion research, which has shown that impacts with rotational acceleration/deceleration inside the skull are the most damaging. Based on the yolk’s deformation, such impacts likely stretch neurons and disturb their delicate network. (Image credit: cracked egg – K. Nielsen, others – J. Lang et al.; research credit: J. Lang et al.; via Physics World; submitted by Kam-Yung Soh)
February 16, 2021
Strings of Swirls
Von Karman vortex streets are the rows of alternating vortices shed off isolated objects interrupting a flow. Here, the volcanic peaks of Cabo Verde disrupt an atmospheric flow accustomed to an empty ocean. In a steady wind, air wraps around the volcanoes and detaches first on one side, creating a vortex, then from the other side, making a vortex of the opposite rotation. Although these structures are always present, we only see them when they stir up the cloud layer, leaving these strings of swirls for hundreds of kilometers behind the islands. (Image credit: L. Dauphin/NASA; via NASA Earth Observatory)
February 15, 2021
Viscoplastic Drop Impact
There are many materials that don’t behave exactly as a fluid or a solid, instead displaying characteristics of both. In this video, we see drops of hair gel falling into water. The gel is viscoplastic – showing some of the viscous behavior of a fluid and some of the plastic behavior (the inability to change back to its initial shape) of a solid.
On impact, the gel deforms due to the forces on it, but the final shape does not depend solely on the amount of force; instead, it’s the rate at which the forces are applied that determines the final shape. By tuning the impact speed and the gel stiffness, it’s possible to make many final capsule shapes, something that could be useful in applications like drug manufacturing. (Image and video credit: M. Jalaal et al.)
February 12, 2021
Flexible Wings Aid Butterfly Flight
Butterflies are some of the oddest flyers of the insect world, given the large size of their wings relative to their bodies. That could be a recipe for inefficient flight, but a new study shows that butterflies’ large flexible wings actually help them take off quickly.
When lifting their wings, butterflies use an unusual clapping motion, with the leading edges of their wings coming together before the rest of the wings. This motion helps cup and direct air, creating most of the butterfly’s thrust, according to the researchers. The wings’ flexibility is key to this. Using artificial wings — both stiff and flexible — researchers found that the flexible wings generated 22% more useful impulse and were 28% more efficient. For a tiny flyer with frequent take-offs, that’s an enormous savings! (Image, video, and research credit: L. Johansson and P. Henningsson; via BBC; submitted by Kam-Yung Soh)
February 11, 2021
Chasing Tornadoes
Tornadoes are some of the most powerful storms on Earth. Their difficult-to-predict nature means that we still have a relatively scant understanding of exactly how they form. We know the conditions that promote their development — warm, moist rising air, wind shear, and rotation — but how and when those translate into a dangerous funnel cloud is harder to pin down. In this video, we hear from one of National Geographic’s storm researchers, Anton Seimon, who chases these storms in search of answers. (Image and video credit: National Geographic)
February 10, 2021
Inside Drying Wood
Wood must dry before it can be used in most applications, but with its complex internal structure exactly how wood dries out has been unclear. New experiments combining MRI and x-ray imaging reveal a process quite different than expected.
Inside hardwoods like poplar — the species studied here — wood contains both solid structures and pores where water can gather. The pores do not form a fully interconnected network, so capillary action alone is unable to carry water through the pores and out to a surface where it can evaporate.
Instead, researchers found that water evaporating at the surface came from so-called “bound water” in the wood’s solid structures. As the bound water evaporated, it caused water in the wood pores to diffuse into the solid walls, becoming bound and continuing to feed the evaporation. (Image and research credit: H. Penvern et al.; via APS Physics)
February 9, 2021
“Chocolate Lullaby”
In this music video for the song “Chocolate Lullaby,” the Macro Room team feature all kinds of fluid dynamical phenomena. It begins with pouring viscous fluids, which, like honey or cake batter, fold and stack before they spread. From there things get significantly less viscous and more turbulent. There’s some neat coalescence, billowing streams colliding, and some gorgeous turbulence. Enjoy! (Image and video credit: Macro Room)
February 8, 2021
Interview: Fountain Pen Physics
It’s not much of a secret that I love fountain pens. Recently, I got to combine two of my passions by explaining fountain pen physics on the Stationery Orbit podcast. Check out my episode here. (Image credit: N. Sharp)
February 7, 2021
Permeable Pavement
Controlling storm water is a major challenge in urban environments, where many surfaces are impermeable. In a city, rain cannot simply soak into the ground and filter into the water table. One potential solution is permeable pavement, which uses the same ingredients as its common counterpart minus the sand that usually packs into gaps between the gravel. Without the sand, the final pavement allows water to soak through, as seen above. In practice, the water sinks into a porous reservoir beneath the pavement that helps store and regulate the water’s discharge into the soil.
Unfortunately, this solution has its limitations. Permeable pavement is not as strong as the regular variety, so it doesn’t work for highly trafficked areas like roadways. It’s also not well-suited to colder areas, where freezing and thawing may disrupt its operation. But it is another tool in engineers’ toolboxes when it comes to keeping urban environments in harmony with nature’s needs. (Image and video credit: Practical Engineering)
February 5, 2021
Cutting Coronavirus Risk in Cars
Even in a pandemic, it’s sometimes necessary to share a car with someone outside one’s bubble. When that’s the case, it’s important to know how to limit risks of coronavirus exposure. For this study, researchers used computational fluid dynamics to simulate flow around and inside a Prius-like four-door sedan with a driver and a single passenger located in the rear passenger-side seat. Assuming the air conditioner was on and the car was moving at 50 miles per hour, the researchers found that the baseline flow of air inside the car moves from the back of the cabin toward the front. With the windows closed, the simulation suggested that 8-10% of the aerosol particles exhaled by one passenger could reach the other.
Opening the car’s windows increases the ventilation and reduces exposure risk. The best configuration the researchers found opened two windows: the front passenger-side window and the rear driver-side window. By opening the window opposite each person, the airflow in the car creates a sort of curtain between the two that reduces aerosol exposure to only 0.2-2% of what’s exhaled by the other occupant. (Image credit: rideshare – V. Xok, CFD – V. Mathai et al.; research credit: V. Mathai et al.; via NYTimes; submitted by Kam-Yung Soh)
February 4, 2021