Tag: history

The Best of FYFD 2025
Happy 2026! This will be a big year for me. I’ll be finishing up and turning in the manuscript for my first book — which flows between cutting edge research, scientists’ stories, and the societal impacts of fluid physics. It’s a culmination of 15 years of FYFD, rendered into narrative. I’m so excited to share it with you when it’s published in 2027.
As always, though, we’ll kick off the year with a look back at some of FYFD’s most popular posts of 2025. (You can find previous editions, too, for 2024, 2023, 2022, 2021, 2020, 2019, 2018, 2017, 2016, 2015, and 2014.) Without further ado, here they are:
What a great bunch of topics! I’m especially happy to see so many research and research-adjacent posts were popular. And a couple of history-related posts; I don’t write those too often, but I love them for showing just how wide-ranging fluid physics can be.
Interested in keeping up with FYFD in 2026? There are lots of ways to follow along so that you don’t miss a post.
And if you enjoy FYFD, please remember that it’s a reader-supported website. I don’t run ads, and it’s been years since my last sponsored post. You can help support the site by becoming a patron, buying some merch, or simply by sharing on social media. And if you find yourself struggling to remember to check the website, remember you can get FYFD in your inbox every two weeks with our newsletter. Happy New Year!
(Image credits: droplet – F. Yu et al., starlings – K. Cooper, espresso – YouTube/skunkay, fountain – Primal Space, Uranus – NASA, turbulence – C. Amores and M. Graham, capsule – A. Álvarez and A. Lozano-Duran, melting ice – S. Bootsma et al., puquios – Wikimedia, cooling towers – BBC, solar wind – NASA/APL/NRL, Lake Baikal – K. Makeeva, sprite – NASA, roots – W. van Egmond, sunflowers – Deep Look)
1. I know what I did. ↩︎
Fediverse Reactions
January 1, 2026
Engineering the City of Venice
In 452, Roman refugees established what became the city of Venice across a series of low-lying marshy islands in a lagoon. With no solid ground available, Venice has needed clever engineering for its infrastructure, as discussed in this Primal Space video. That started with building the first piles — which still survive to this day — by driving long timbers down into harder clay levels. Because these wooden poles sit entirely below the water and are capped with stone foundations, they are preserved against rotting.
As Venice grew over the next thousand years, its citizens had other infrastructure problems to solve. When fresh water needs outstripped what could be delivered by boat from the mainland, Venetians redesigned the substructure of each square to capture, filter, and store rainwater. And to wash away waste, they designed tunnels that use gravity and the daily tides to flush out sewage. (Video and image credit: Primal Space)
September 9, 2024
Feynman’s Sprinkler Solved
In graduate school, my advisor introduced us to a particularly vexing fluid dynamical thought experiment known as the Feynman sprinkler. After observing an S-shaped sprinkler that rotated when water shot out its arms, physicist Richard Feynman wondered what would happen if the device were placed in a tank of water with the flow reversed. If the sprinkler was sucking in water, would it rotate and, if so, in what direction?
This seemingly simple question has confounded physicists ever since, in part because you can make believable arguments for multiple different results. Attempts to build the apparatus experimentally produced differing results, too — often due to variables that don’t appear in the thought experiment, like friction in the sprinkler’s bearing. But, at long last, a group posits they have the final answer to the problem.
They cleverly built their sprinkler so that it floats in its tank, with the addition or removal of water from the sprinkler controlled by a second siphon-connected tank. With no solid-solid contacts, the sprinkler can rotate with very little friction.
Flow visualization of the sprinkler in reverse (suction) mode. For image clarity, the device is held in place to prevent spinning. Notice how the jets coming into the hub glance off one another and form counter-rotating vortex pairs at an angle. This asymmetry is the source of the sprinkler’s rotation when allowed to move.
The team found that sucking water into the sprinkler does, indeed, reverse the sprinkler’s rotation, but it’s not a simple reversal of the forward sprinkler’s flow. To see why, check out the video above, which visualizes flow inside the sprinkler during suction. For clarity, the device is held fixed in place during flow visualization. Notice that the two arms of the sprinkler sit directly opposite one another in the hub. Thus, you’d expect their two jets to collide and form counter-rotating vortices along a vertical axis. But the vortex pairs are offset from the centerline.
This asymmetry takes place because the velocity profiles of flow across the hub inlets are skewed. Instead of the largest velocity occurring on the centerline of the inlet, each occurs slightly to one side. So when the jets collide, they do so off-center and impart a torque to the sprinkler. The reason for the skewed profiles at the inlets lies further upstream in the curved arms of the sprinkler. Centrifugal force from turning the corner leaves a mark on the flow, leading, ultimately, to the skewed velocity profiles, offset jets, and spinning sprinkler. (Image and research credit: K. Wang et al.; via APS Physics)
February 22, 2024
Remembering Rivers Past
Our landscapes have changed dramatically over the last 200 years of urban development, but traces of the land’s past still remain. Many streams and rivers that once ran on the surface persist in underground culverts. Bruce Willen’s “Ghost Rivers” installation highlights the path of one such waterway, Sumwalt Run, which flows across what is now the Remington and Charles Village neighborhoods of Baltimore. The project includes ten installations that describe the hidden water and its history as well as a wavy, blue line that marks its path. (Image credits: Public Mechanics and F. Hamilton, see alt text; installation: B. Willen; via Colossal)
February 9, 2024
The Best of FYFD 2023
A fresh year means a look back at what was popular last year on FYFD. Usually, I give a numeric list of the top 10 posts, but this year the analytics weren’t as clear. So, instead, I’m combining from a few different sources and presenting an unordered list of some of the site’s most popular content. Here you go:
I’m really pleased with the mix of topics this year; many of these topics are straight from research papers, and others are artists’ works. At least one is both. From swimming bacteria to star-birthing nebulas, fluid dynamics are everywhere!
If you enjoy FYFD, please remember that it’s a reader-supported website. I don’t run ads and it’s been years since my last sponsored post. You can help support the site by becoming a patron, making a one-time donation, buying some merch, or simply by sharing on social media. And if you find yourself struggling to remember to check the website, remember you can get FYFD in your inbox every two weeks with our newsletter. Happy New Year!
(Image credits: sphinx – S. Boury et al., ear model – S. Kim et al., maze – S. Mould, dandelion – S. Chaudhry, water tank – P. Ammon, e. coli – R. Ran et al., drop impact – R. Sharma et al., Leidenfrost – L. Gledhill, toilet – J. Crimaldi et al., engine sim – N. Wimer et al., rivers – D. Coe, fin – F. Weston, snake – P. Schmid, nebula – J. Drudis and C. Sasse, flames – C. Almarcha et al.)
January 1, 2024
Eroding the Sphinx
One theory suggests that the Great Sphinx of Giza formed — in part — naturally as a result of erosion, and ancient Egyptians added features to the bedrock formation. To test the plausibility of the theory, researchers made a miniature sphinx, consisting of a clay mound with a single, harder inclusion to represent the Sphinx’s head, and placed their construction in a water tunnel. As the water eroded away the clay, the head appeared, and flow around this harder-to-erode region formed some of the body and paws of the reclining Sphinx.
The experiment suggests that it is plausible for part of the Sphinx to have formed naturally, as a result of erosion. But plausibility is not proof, and given the lack of a contemporary inscription explaining the statue’s origin, the goals and methods of the people who built it around 2500 B.C.E. will remain a matter of archaeological debate. (Image credit: S. Boury et al.)
October 30, 2023
Deciphering Krakatau
In 1883, the eruption of Krakatau (also called Krakatoa) shook the world, sending shock waves and tsunamis ricocheting across the globe. Some of the smaller waves hit shorelines in the Atlantic and Pacific that were entire continents and ocean basins away from the original explosion. At the time, scientists were so perplexed by the phenomenon that they blamed coincidental earthquakes for the wave action.
Only when Tonga experienced a similarly devastating volcanic eruption earlier this year were scientists able to verify what they’d long suspected: these smaller tsunamis were not caused by solid material displacing water; instead they are the result of atmospheric pressure waves coupling to the ocean. Follow the full story over at Quanta. (Image credit: M. Barlow; via Quanta; submitted by Kam-Yung Soh)
May 9, 2022
Dead Water
In the days before motorized propulsion, sailors would sometimes find themselves slowed nearly to a stop by what they called ‘dead water‘. As discovered in laboratory experiments over a century ago by Vagn Walfrid Ekman, the dead water phenomenon occurs where a layer of fresh water exists over saltier water. The ship’s motion generates internal waves in the salty layer, which in turn causes substantial additional drag on the boat. In a related phenomenon, named for Ekman, the internal waves generated by a boat’s initial acceleration cause its speed to fluctuate.
While these phenomena have little effect on today’s shipping, they can be relevant for swimmers in areas like harbors and fjords where fresh water meets the sea. And their effects were undoubtedly substantial for much of history. There is even speculation that dead water might have caused the defeat of Mark Antony and Cleopatra’s superior navy at the hands of Octavian’s smaller ships in the Battle of Actium. (Image credit: M. Blum; research credit: J. Fourdrinoy et al.; via Hakai Magazine; submitted by Kam-Yung Soh)
November 18, 2020
The Boston Molasses Flood
Today marks the 100th anniversary of the Boston Molasses Flood, and to commemorate this bizarre disaster, I’ve made a video about the key findings from my research with colleagues at Harvard University. Check it out below!
And, if you’re still hankering to learn more about the Molasses Flood, here are some recent articles and interviews on the subject:
– Boston.com
– NBC News
– New England News Collective
– Historium Unearthia podcast
(Video and image credits: N. Sharp)
January 15, 2019
The Great Smog of London
Our atmosphere is active and ever-changing – except when it isn’t. Some areas, including many cities, are prone to what’s known as a temperature inversion, where a layer of cooler air gets trapped underneath a warmer one. Because this means that a dense layer is caught under a less dense one, the situation is stable and – absent other changes in circumstances – will stick around. There are several ways this can happen, including overnight when areas near the ground cool faster than the atmosphere higher up.
When temperature inversions persist, they can trap pollutants and create health hazards. One of the worst of these recorded occurred in December 1952 in London. An anticyclone created a temperature inversion over the city that trapped smoke from coal burned to warm homes and reduced visibility – sometimes even indoors – to only a meter or two. Thousands of people died from the respiratory effects of the five-day smog, and it prompted major efforts to improve emissions and air quality. Temperature inversions cannot be avoided, but the Great Smog of London taught us the necessity of reducing their danger. (Image credit: Getty Images)
December 10, 2018