Search results for: “lift”

How Wings Create Lift
One of the topics in fluid dynamics almost everyone has come across is the explanation of how airplanes produce lift. Using Bernoulli’s principle–which relates velocity and pressure–and a picture of an airfoil, your average science text will say that a bit of air going over the top of the airfoil has to travel farther than a bit of air going under the airfoil, and that, therefore, the air over the top travels faster than the air under the airfoil.
Unfortunately, this is misleading and, depending on the wording, outright wrong! The hidden assumption in this explanation is that air that goes over the top and air that goes under the bottom have to reach the trailing edge of the airfoil at the same time. But why would that be? (As one of my profs once said, “There is nothing in physics that says there is Conservation-Of-Who-You-Were-Sitting-Next-To-When-You-Started.”)
Take a look at the video above. It shows an airfoil in a wind tunnel using smoke visualization to show how the air moves. Around the 0:25 mark, the video slows to show a pulse of smoke traveling over the airfoil. What happens at the trailing edge? The smoke going over the top of the airfoil is well past the trailing edge by the time the smoke going under the airfoil reaches the trailing edge!
It’s true that air goes faster over the top of the airfoil than the bottom and that this causes a lower pressure on top of the airfoil (as Bernoulli tells us it should) and that this causes an upward force on the airfoil. But which causes which is something of a chicken-and-egg problem.
A more straightforward way, in my opinion, of explaining lift on an airplane is by thinking about Newton’s 3rd law: for every action, there is an equal and opposite reaction. Take a look at the air’s movement around the airfoil as the angle of attack is increased around 1:00 on the video. Just in front of the airfoil, the air is moving upward. Just after the airfoil, the air is pointed downward. A force from the airfoil has pushed the air down and changed its direction. By Newton’s 3rd law, this means that the air has pushed the airfoil up by the same amount. Voila! Lift!
September 8, 2010
Buccaneer Archipelago
Off western Australian, hundreds of low-lying islands and coral reefs jut into the ocean as part of the Buccaneer Archipelago. Tides here have a range of nearly 12 meters, so water rips through the narrow channels as the tide ebbs and flows. These fast flows lift sediment that dyes the water a bright turquoise. (Image credit: M. Garrison; via NASA Earth Observatory)
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November 5, 2025
Flettner Rotors Spin Anew
In the 1920s, the world saw a new sort of marine propulsion, ships with one or more tall, smokeless cylinders. These Flettner rotors, named for their inventor, would spin in the wind, generating lift to propel the boat, much as a sail would. (The difference is that the rotor uses the Magnus effect.)
The market crash that kicked off the Great Depression spelled an end to the rotorship, but the idea is getting revived as industries search for greener forms of ship propulsion. Although the Flettner rotor still uses fuel (to spin the rotor), it can complete a voyage on only a small fraction of the fuel needed for conventional propulsion. (Image credit: Getty Images; via PopSci)
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October 16, 2025
Smoke Bomb
With a flurry of motion along its pectoral fin, a sting ray lifts the sand nearby and disappears into the turbid cloud. This tactic helps the animal both hide and escape. In a similar move, sting rays and other bottom-dwelling fish can bury themselves in sand.(Image credit: Y. Coll/OPOTY; via Colossal)
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September 19, 2025
Cutting Out Canyons
Over the millennia, the Colorado River has carved some of the deepest and most dramatic canyons on our planet. This astronaut photo shows the river near its dam at Lake Powell. The strip of white edging the lake is the “bathtub ring” that shows how the water level has varied over the years. The deep canyons — over 400 meters from the Horn in the center of the photo to the river beside it — throw shadows across the landscape. To reach these depths, the Colorado River incised its path into bedrock that was tectonically uplifted. (Image credit: NASA; via NASA Earth Observatory)
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August 4, 2025
Branching Dendrites
This award-winning aerial image by photographer Stuart Chape shows a tidal creek in Lake Cakora, New South Wales, Australia. At first glance, it looks much like any river delta, with branching dendritic paths that split into smaller and smaller waterways. That’s deceptive, though, because very different forces shape this creek. Because tides move in and out, a tidal creek is home to flows that move both directions — toward and away from the branches. That also means that flow speeds can change rapidly as the tides shift, which in turn changes which sediments get lifted, dropped, and moved around the creek bed. (Image credit: S. Chape/IAPOTY; via Colossal)
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July 25, 2025
Flying Foxes
A sweltering day in India brought out the local giant fruit bats (also called Indian flying foxes) to keep cool in the river. Normally nocturnal, they made a rare daytime appearance to beat the heat. Wildlife photographer Hardik Shelat was lucky enough to catch these awesome images of the bats in flight. True to their name, the animals have wingspans ranging from 1.2 to 1.5 meters, which should give them some impressive lift, even when gliding down near the water. (Image credit: H. Shelat; via Colossal)
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July 4, 2025
Seeing the Sun’s South Pole For the First Time
The ESA-led Solar Orbiter recently used a Venus flyby to lift itself out of the ecliptic — the equatorial plane of the Sun where Earth sits. This maneuver offers us the first-ever glimpse of the Sun’s south pole, a region that’s not visible from the ecliptic plane. A close-up view of plasma rising off the pole is shown above, and the video below has even more.
Solar Orbiter will get even better views of the Sun’s poles in the coming months, perfect for watching what goes on as the Sun’s 11-year-solar-cycle approaches its maximum. During this time, the Sun’s magnetic poles will flip their polarity; already Solar Orbiter’s instruments show that the south pole contains pockets of both positive and negative magnetic polarity — a messy state that’s likely a precursor to the big flip. (Image and video credit: ESA & NASA/Solar Orbiter/EUI Team, D. Berghmans (ROB) & ESA/Royal Observatory of Belgium; via Gizmodo)
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June 30, 2025
Flamingo Fluid Dynamics, Part 2: The Game’s a Foot
Yesterday we saw how hunting flamingos use their heads and beaks to draw out and trap various prey. Today we take another look at the same study, which shows that flamingos use their footwork, too. If you watch flamingos on a beach, in muddy waters, or in a shallow pool, you’ll see them shifting back and forth as they lift and lower their feet. In humans, we might attribute this to nervous energy, but it turns out it’s another flamingo hunting habit.
As a flamingo raises its foot, it draws its toes together; when it stomps down, its foot spreads outward. This morphing shape, researchers discovered, creates a standing vortex just ahead of its feet — right where it lowers its head to sample whatever hapless creatures it has caught in this swirling vortex. And the vortex, as shown below, is strong enough to trap even active swimmers, making the flamingo a hard hunter to escape. (Image credit: top – L. Yukai, others – V. Ortega-Jimenez et al.; research credit: V. Ortega-Jimenez et al.; submitted by Soh KY)
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June 4, 2025
Flamingo Fluid Dynamics, Part 1: A Head in the Game
Flamingos are unequivocally odd-looking birds with their long skinny legs, sinuous necks, and bent L-shaped beaks. They are filter-feeders, but a new study shows that they are far from passive wanderers looking for easy prey in shallow waters. Instead, flamingos are active hunters, using fluid dynamics to draw out and trap the quick-moving invertebrates they feed on. In today’s post, I’ll focus on how flamingos use their heads and beaks; next time, we’ll take a look at what they do with their feet.
Feeding flamingos often bob their heads out of the water. This, it turns out, is not indecision, but a strategy. Lifting its flat upper forebeak from near the bottom of a pool creates suction. That suction creates a tornado-like vortex that helps draw food particles and prey from the muddy sediment.
When feeding, flamingos will also open and close their mandibles about 12 times a second in a behavior known as chattering. This movement, as seen in the video above, creates a flow that draws particles — and even active swimmers! — toward its beak at about seven centimeters a second.
Staying near the surface won’t keep prey safe from flamingos, either. In slow-flowing water, the birds will set the upper surface of their forebeak on the water, tip pointed downstream. This seems counterintuitive, until you see flow visualization around the bird’s head, as above. Von Karman vortices stream off the flamingo’s head, which creates a slow-moving recirculation zone right by the tip of the bird’s beak. Brine shrimp eggs get caught in these zones, delivering themselves right to the flamingo’s mouth.
Clearly, the flamingo is a pretty sophisticated hunter! It’s actively drawing out and trapping prey with clever fluid dynamics. Tomorrow we’ll take a look at some of its other tricks. (Image credit: top – G. Cessati, others – V. Ortega-Jimenez et al.; research credit: V. Ortega-Jimenez et al.; submitted by Soh KY)
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June 3, 2025

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