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Category: Phenomena

PyeongChang 2018: Bobsleigh
In bobsleigh, two- and four-person teams compete across four runs down an ice track. The shortest cumulative time wins, and since typical runs are separated by hundredths of a second, teams look for any advantage that helps them shave time. The size, weight, and components of a sled are restricted by federation rules; for example, teams cannot use vortex generators to improve their aerodynamics. Instead bobsledders work with companies like BMW, McLaren, and Ferrari to engineer their sleds. Both computational fluid dynamics and wind tunnel tests with the actual team in the sled are used to make each sled as aerodynamic as possible. (Image credit: IOC, Gillette World Sports, source)
February 20, 2018
PyeongChang 2018: Snow-Making
These days artificial snow-making is a standard practice for ski resorts, allowing them to jump-start the early part of the season. Snow guns continuously spray a mixture of cold water and particulates 5 or more meters in the air to generate artificial snow. The tiny droplet size helps the water freeze faster and the particles provide nucleation sites for snow crystals to form. As with natural snow, the shape and consistency of the snow depends on humidity and temperature conditions. Pyeongchang is generally cold and dry, so even the artificial snow there tends to be similar to snow in the Colorado Rockies. Recreational skiers tend to look down on artificial snow, but Olympic course designers actually prefer it. With artificial snow, they can control every aspect of an alpine course. For them, natural snowfall is a disruption that puts their design at risk. (Video credit: Reactions/American Chemical Society)
February 19, 2018
PyeongChang 2018: Speedskating
Four years ago in Sochi, Under Armour’s suits for the U.S. speedskating team took a lot of flak after the team failed to medal. The company defended the physics and engineering of their suits, and an internal audit of the speedskating program ultimately placed blame on flaws in their training regimen, unfamiliarity with the new suits, and overconfidence.
This time around Under Armour has taken a more hands-on approach with the team, helping with training regimens in addition to providing suits. Under Armour spent hundreds of hours testing the suits in Specialized’s wind tunnel, including testing many fabrics before settling on the slightly rough H1 fabric used in patches on the skater’s arms and legs. Like the previous suit’s dimpled design, the roughness of the fabric promotes turbulent flow near it. Because turbulent flow follows curved contours better than laminar flow does, air stays attached to the athlete for longer, thereby reducing their drag. The suit is also designed with asymmetric seams that help the athlete stay low and comfortable in the sport’s frequent left turns.
U.S. speedskaters have been competing in a version of the suits since last winter, ensuring that athletes are familiar with the equipment this time around. Whether the new suits and training program will pay off remains to be seen. After their disastrous experience in Sochi, both the team and the company are shy about setting expectations. (Image credits: D. Maloney/Wired; US Speedskating)
February 16, 2018
PyeongChang 2018: Skeleton
Skeleton, the sliding event in which athletes race down an ice track head first, is a fast-paced and punishing sport. Skeleton racers can reach speeds of 125 kph (~80 mph) during their descents. This is a little slower than the feet-first luge, in part because the skeleton sled runs on circular bars rather than sharp runners.
Body positioning is key in the sport. It’s the athlete’s primary method of steering, and it controls how much drag slows them down. But skeleton runs are brutally taxing; athletes pull 4 or 5g in the turns – more than astronauts experience during a launch! All that jostling means athletes cannot stand more than about 3 trips down the track in a day. To practice positioning without the bone-jarring descent, athletes can work in a wind tunnel. While the wind tunnel provides the aerodynamic equivalent of their usual speed, athletes focus on holding their bodies in the most streamlined position. Some wind tunnels are even able to provide screens that let the athletes see their drag values in real-time, letting them adjust to learn what works best for them. (Image credit: N. Pisarenko/AP, Bromley Sports)
February 15, 2018
PyeongChang 2018: Ski Jumping
No winter sport is more aerodynamically demanding than ski jumping. A jump consists of four parts: the in-run, take-off, flight, and landing. The in-run is where an athlete gains her speed, and to keep drag from slowing her down, she descends in a streamlined tuck that minimizes frontal area. The biggest aerodynamic challenge comes during flight, when the jumper wants to maximize lift while minimizing drag. The athlete spreads her skis in a V-shape and flattens her body, using her hands to adjust her flight. Flying the farthest requires careful management of forces while in the air. Wind plays a major role as well, with headwinds helping athletes fly farther. To compensate, scoring includes a wind factor calculated based on conditions for each jump. (Image credit: B. Pieper, Reuters/K. Pfaffenbach, PyeongChang 2018)
February 14, 2018
Crevasses
Glacial ice is constantly flowing but at speeds we don’t notice by eye. That doesn’t mean there aren’t signs, though! Crevasses, narrow fractures in the ice that may be tens of meters deep, are a sign of those flows. Crevasses form in areas where the ice is under high stress. That could be a spot where the ice is flowing down a steeper incline or a place where multiple ice flows merge. Researchers can even use ice-penetrating radar to locate buried crevasses deep inside the ice. These are remnants of past flow conditions and provide hints at how the ice flows have changed over time. Crevasses are also a path for meltwater to penetrate deep into the ice, which can change slip conditions at the base of the glacier and increase both flow and melt rates. (Image credit: NASA/Digital Mapping Survey; via NASA Earth Observatory)
February 8, 2018
The Drinking Bird
At first glance, the drinking bird is a simple desk toy, but the physics and engineering behind the device is clever enough to have challenged many great minds. In this video, Bill Hammack dissects the drinking bird, revealing the heat engine beneath the felt and feathers. The bird’s drinking is driven by thermodynamics and the relative pressures of fluids in its head and body. When the beak is wetted, fluid wicks up the felted head and slowly evaporates, thereby cooling the vapor inside the head. Some of that vapor condenses, lowering the vapor pressure in the head and allowing liquid to rise from the body. When enough fluid reaches the head, the bird tips forward. This allows vapor to rise up the liquid column into the head, equalizing the pressure between the two ends. The bird sits up with a freshly wetted head and starts the cycle over. Check out the full video for more detail, including a look at what other methods can drive the bird, including bourbon and light bulbs. (Video and image credit: B. Hammack; via J. Ouellette)
February 5, 2018
The Lava Lamps That Secure the Internet
A wall of lava lamps in a San Francisco office currently helps keep about 10% of the Internet’s traffic secure. Internet security company Cloudflare uses a video feed of the lava lamps as one of the inputs to the algorithms they use to generate large random numbers for encryption. The concept dates back to a 1996 patent for a product called LavaRand. The idea is that using a chaotic, unpredictable source as a seed for random number generators makes it much harder for an adversary to crack your encryption.
With lava lamps, a lot of that chaos comes from the fluid dynamics involved – without perfect knowledge of thousands of variables, it would be impossible to simulate the lava lamp wall and get the same outcome as the real one – but there’s also randomness that comes from the measurement. People walking by, shifts in lighting, and random fluctuations of individual pixels all help make the video feed unpredictable. For those interested in the details of how Cloudflare uses their lava lamps, the company explains things for both technical and non-technical readers. You can also check out Tom Scott’s video for a good overview. (Image and video credit: T. Scott; submitted by Jean H.)
January 18, 2018
Seeing the Wake
Hot exhaust gases churn in the wake of this climbing B-1B Lancer. The high temperature of the exhaust changes the density and, thus, the refractive index of the gases relative to the atmosphere. Light traveling through the exhaust gets distorted, making the highly turbulent flow visible to the human eye. Note how the four individual engine exhaust plumes quickly combine into one indistinguishable wake. This is typical for turbulence; it’s hard to track where any given fluctuations originally came from. The airplane’s wingtip vortices are just visible as well, if you look closely. (Image credit: T. Rogoway; submitted by Mark S.)
January 15, 2018
Pilot-Wave Hydrodynamics: Resources
This is the final post in a collaborative series with FYP on pilot-wave hydrodynamics. Previous posts: 1) Introduction; 2) Chladni patterns; 3) Faraday instability; 4) Walking droplets; 5) Droplet lattices; 6) Quantum double-slit experiments; 7) Hydro single- and double-slit experiments; 8) Quantum tunneling; 9) Hydrodynamic tunneling; 10) de Broglie’s pilot-wave theory
Thanks for joining us this week as we explored nearly two centuries’ worth of scientific discoveries around vibration, fluid dynamics, and quantum mechanics. For those who’d like to learn more about these and related topics, we’ve compiled some helpful resources below.
Other Videos, Articles, and Resources by Topic
Chladni Patterns
- ANSYS, “Chladni Plates”
- Brusspup, “Amazing Resonance Experiment!”
- Kenichi Kanazawa, “Color Sound”
- Microfluidic Chladni patterns
- Nigel Stanford, “Cymatics”
- Peter Remco, “Chladni patterns in a violin plate”
- Steve Mould, “Random couscous snaps into beautiful patterns”
Faraday Instability
- FYFD, Alligators and water dancing
- FYFD, Liquid crystals vibrating on a tuning fork
- Gallery of Fluid Motion, “The Tibetan singing bowl”
- Nigel Stanford, “Cymatics”
- Slow Mo Guys, “Chinese spouting bowl in slow motion.”
Quantum Mechanics
- Workgroup Bohmian Mechanics Channel
Pilot-wave Hydrodynamics
- Dual Walkers, learn about the physics from the researchers themselves
- Gallery of Fluid Motion, “The pilot-wave dynamics of walking droplets.”
- Gallery of Fluid Motion, “Shedding light on pilot-wave phenomena.”
- The Lutetium Project, “Never-ending bouncing droplets.”
- The Lutetium Project, “Dual walkers: drops and waves.”
- Through the Wormhole, Interview with Y. Couder
- Wired, “Have we been interpreting quantum mechanics wrong this whole time?”
- Veritasium, “Is this what quantum mechanics looks like?”
Selected (Academic) Bibliography by Topic
Articles marked with an asterisk (*) are recommended for their approachability and/or broad overview of the subject.
Chladni Patterns
- (*) M. Faraday, “On a peculiar class of acoustical figures; and on certain forms assumed by groups of particles upon vibrating elastic surfaces,” 1831.
- Lord Rayleigh, “On the circulation of air observed in Kundt’s tubes, and on some allied acoustical problems,” 1884.
- H. van Gerner et al., “Air-induced inverse Chladni pattern,” 2011.
Faraday Instability
- (*) M. Faraday, “On a peculiar class of acoustical figures; and on certain forms assumed by groups of particles upon vibrating elastic surfaces,” 1831.
Pilot-wave Hydrodynamics
- Y. Couder and E. Fort, “Single-particle diffraction and interference at a macroscopic scale,” 2006.
- A. Eddi et al., “Unpredictable tunnel of a classical wave-particle association,” 2009.
- (*) Y. Couder et al., “Walking droplets: A form of wave-particle duality at macroscopic scale?”, 2010.
- J. Molacek and J. Bush, “Droplets bouncing on a vibrating bath,” 2013.
- J. Molacek and J. Bush, “Droplets walking on a vibrating bath: toward a hydrodynamic pilot-wave theory,” 2013.
- D. Harris et al., “Wave-like statistics from pilot-wave dynamics in a circular corral,” 2013.
- O. Wind-Willassen et al., “Exotic states of bouncing and walking droplets,” 2013.
- (*) J. Bush, “Pilot-wave hydrodynamics,” 2015.
- D. Harris et al., “Visualization of hydrodynamic pilot-wave phenomena,” 2016.
(Image credit: A. Labuda and J. Belina)
January 12, 2018

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