Gram for gram, few animals can match the power of a pistol shrimp’s snap. When its claw closes, the shrimp ejects a jet of water so fast that the water pressure drops below the vapor pressure, causing a cavitation bubble. Like other cavitation bubbles, this one is short-lived, growing and collapsing (and sending out shock waves!) in less than a millisecond. That’s enough to knock any predator or prey for a loop. (Image and video credit: Ant Lab)
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Galapagos Week: Pistol Shrimp
One of the most striking things about snorkeling in the Galapagos was how loud it was underwater. There were hardly any boats nearby, but every time my ears dipped below the surface, I could hear a constant cacophony of sound. Some it came from waves against the sand, some of it was the sound of parrotfish nibbling on coral, but a lot of it was likely the work of a culprit I couldn’t see hidden in the sand: the pistol shrimp.
These small crustaceans hunt with an oversized claw capable of snapping shut at around 100 kph. When the two halves of the claw come together, they push out a high-speed jet of water. High velocity means low pressure – a low enough pressure, in fact, to drop nearby water below its vapor pressure, causing bubbles to form and expand. These cavitation bubbles collapse quickly under the hydrostatic pressure of the surrounding water, creating a distinctive pop that makes the pistol shrimp one of the loudest sea creatures around. (Image credit: BBC Earth Unplugged, source; research credit: M. Versluis et al.)
All week we’re celebrating the Galapagos Islands here on FYFD. Check out previous posts in the series here.

The Pistol Shrimp’s Secret Weapon
The pistol shrimp (or pistol crab) is a finger-sized crustacean with a fluid dynamical superpower. When it snaps its claw, a jet of water shoots out so quickly (62 mph) that a low-pressure bubble forms in its wake. When the bubble collapses, it emits a bang and a flash of light in a process known as sonoluminescence. The whole event takes less than 300 microseconds. The light emitted suggests that temperatures inside the bubble reach 5,000 degrees Kelvin, around the temperature of the surface of the sun. #

4th Birthday: Mantis Shrimp
Undoubtedly one of the most mind-boggling instances of fluid dynamics I’ve learned about in writing FYFD is that of sonoluminescence – an effect in which light is produced from imploding cavitation bubbles. In a laboratory, the effect is usually initiated with acoustic waves. A bubble can be forced to oscillate and collapse periodically when forced by the sound. During the collapse, the vapor inside the bubble reaches temperatures of the order of thousands of Kelvin, and light is produced. What is far more wild, though, is that the effect occurs in nature as well. Both the pistol shrimp and the mantis shrimp produce the effect. As shown in the video above, the mantis shrimp swings its club-like arm with such speed that the local pressure drops below the vapor pressure, causing a cavitation bubble to form and sonoluminescence to occur. Some real Mortal Kombat finishing move s&#% there, indeed. (Video credit: Z. Frank)
Themed Series
Occasionally, FYFD will feature a series of posts on a special theme. This page serves as an archive of these themed series. Got an idea for theme? You can always suggest one via Tumblr, Twitter, or email.

Fluid Dynamics of Plants
- Introduction: previous plant posts
- The extraordinary flight of the dandelion seed
- Bladderworts use ultra-fast suction to catch prey
- Moisture allows horsetail plant spores to walk and jump
- The structure of citrus peels sprays oil at up to 30 m/s

Collective Motion of Humans and Animals
- What makes flocks of birds and schools of fish so hard to predict?
- The solid and fluid characteristics of black aquatic worms
- What crowds of people and granular materials have in common
- The shimmering of giant honeybees
- When collective motion isn’t always beneficial…

PyeongChang Winter Olympics 2018
- What makes ice so slippery
- How moguls form and move
- The gliding flight of a ski jumper
- Aerodynamics of a skeleton run
- How the newest U.S. speedskating suit beats the wind
- How artificial snow gets made
- Wind tunnel testing bobsleds for speed
- Not all Olympic ice is created equal
- Drafting in cross-country skiing
- The odd physics behind curling

Pilot-Wave Hydrodynamics
Completed in collaboration with FYP.- Introduction
- How vibration and Chladni patterns depend on fluids
- Vibrating a liquid creates the ripple-like Faraday instability
- Droplets on a vibrating surface can bounce and even walk
- Bouncing droplets can form lattices
- Quantum double-slit experiments established wave and particle properties for light and electrons…
- …But walking droplets behave the same way in slit experiments
- Quantum tunneling allows electrons to escape…
- …And walking droplets can tunnel out, too!
- So what are the connections between quantum mechanics and pilot-wave hydrodynamics?
- Resources, links, and ways to learn more
(Image credit: D. Harris et al.)

Galapagos Week
- Introducing the Galapagos Islands
- How marine iguanas swim
- What makes the tiny pistol shrimp so loud
- Learning about lava flows: a’a versus pahoehoe
- How blue-footed boobies dive at 20 m/s without breaking their necks
- Sea turtles are aquatic fliers
- Bonus related posts: how frigatebirds cruise the seas without getting wet; the aerodynamics of flying fish; hydrodynamics of humpback whales; incredible bioluminescent plankton; and leaping mobula rays.
(Image credit: N. Sharp and J. Shoer)

Rio Summer Olympics 2016
- How motorbikes can unfairly influence cycling races
- Why swimmers can be faster underwater
- The aerodynamics of rugby
- How to design and build a whitewater course
- The spinning physics of table tennis
- The aerodynamic tactics of track cycling
- How water polo players and synchronized swimmers stay afloat
- How wind and altitude affect the long jump
- Rule 42 and why rocking the boat in sailing is cheating
- The high-speed science of badminton
- Was there a current in the Rio swimming pool?
- What commentators don’t tell you about the perfect diving splash
(Image credit: Getty Images)

A Day in the Life of a Fluid Dynamicist
(Image credit: S. Reckinger et al.)

Walking on Water
- Introduction
- The common basilisk (a.k.a. Jesus Christ lizard)
- Pygmy geckos and other tiny water-walkers
- “Rushing” in Western and Clark’s grebes
- Jumping off water
- How fast does the Flash have to go to run on water?
- Bonus: Calculate what it takes to run on water in English units or metric
(Original grebe image: W. Watson/USFWS)

Fluid Dynamics on Pluto
(Image credit: NASA/JHU APL/SwRI)

FYFD’s Fourth Birthday Celebration
(Image credit: Nat. Geo/BBC2)

Sochi Winter Olympics 2014
- Preview: Wind tunnel testing for ski jumping
- Why ice is slippery
- How lugers slide so fast
- Aerodynamics in long-track speed skating
- How ski jumpers fly farther
- Effects of wind conditions on ski jumping
- The US speedskating suit controversy
- How to make artificial snow
- How skiers glide across snow
- Aerodynamics and technology of bobsledding
- The physics of curling
- Speed skiing
- Link round-up: some of my favorite Olympic science stories
(Image credit: Exa Corp)

Holiday Fluid Dynamics 2013
- Introduction
- The structure of snowflakes
- The aerodynamics of Santa’s sleigh
- Buoyancy-driven Christmas pyramids
- Convection in cocoa
- What’s in a Yuletide fire?
- Bonus: The physics of your New Year’s champagne
(Photo credit: G. Liger-Belair)

Gallery of Fluid Motion Favorites 2013
- Fluid juggling
- Ultrasonic levitation of a droplet
- Leidenfrost droplet propulsion
- Why tapping a beer bottle makes it foam
- Magnetocappillary swimmers
(Photo credit: APS DFD)

Fluid Dynamics and the Ig Nobel Prize
- On the lack of fluid dynamics among Nobel Prize winners
- How a human can run on water
- The physics of cookie dunking
- Does a person swim faster in water or syrup?
- Why shower curtains billow
- Other Ig Nobel fluids winners
- (Added in 2016) The law of urination
(Image credit: Improbable Research)

FYFD’s Third Birthday Celebration
- Introduction
- Visible shock waves from a rocket launch
- Double-spiral so\ap film
- A soap bubble popping
- The fluid dynamic sewing machine
(Photo credit: T. Schnipper et al.)

London Summer Olympics 2012
- The Olympic torch
- What makes a pool fast?
- The aerodynamics of archery
- The physics of badminton
- How cyclists get aero
- How divers minimize splash
- Aerodynamics in running
- How rowers avoid drag
- How javelins fly far
- Why corner kicks swerve
- The aerodynamics of the discus
(Photo credit: AP/Reuters)

Fluid Dynamics of the Tour de France
- The benefits of the peloton
- Crosswinds and the echelon
- The lead-out train
- Aero gear and the time trial
- Wind tunnel testing
(Photo credit: Veeral Patel)

Cavitation in a Bottle
This high-speed video shows the cavitation that occurs when a bottle of water is struck. The impact accelerates the bottle downward, generating localized vacuums between the glass and the liquid. These are cavitation bubbles, which expand until the pressure of the water surrounding them is too great. This outside pressure triggers an implosion of the bubble, which collapses until the pressure within the bubble makes it expand again. These rapid oscillations in pressure can often shatter the glass bottle. Cavitation can also generate extremely high temperatures and even trigger luminescence. It’s used by both pistol shrimp and mantis shrimp to hunt their prey. (Video credit: P. Taylor)

Turning Sound into Light
Sonoluminescence – the creation of light from sound – was discovered in the 1930s, and, due to the difficulty of obtaining direct measurements, the exact mechanism remains highly debated even today. The phenomenon typically takes place within a tiny cavitation bubble inside a liquid. When bombarded with ultrasonic sound, such a bubble will repeatedly expand and collapse. Once a bubble is established, the cycle can be kicked off by increasing the driving acoustic pressure. This will collapse the bubble, drastically increasing its pressure and temperature (up to thousands of degrees Kelvin) and causing the bubble to emit a pulse of light before the pressure imbalance causes it to expand again. Several theories exist as to how the light is generated, the leading one being that the high temperatures in the bubble ionize the noble gases within and that those free electrons emit light via thermal bremstrahlung radiation. Sonoluminescence happens outside the lab, too. Both the previously discussed pistol shrimp and the mantis shrimp generate such light-emitting bubbles when hunting. (Video credit: The Point Studios; suggested by Bobby E.)

Fluids Round-up – 13 July 2013
Prepare yourselves for lots of links in today’s fluids round-up!
- Longtime FYFD favorite Mark Stock (see here, here, and here) and his collaborator James Susinno have unveiled a new interactive art piece, “Everything is Made of Atoms” that utilizes some impressive real-time fluids simulation. NVIDIA’s blog has some details on the computing.
- ScarbsF1 takes a detailed look at the F-duct used to stall an F1 car’s rear wing to reduce drag. (submitted by Vinnie)
- Just in time for summer fun, National Geographic talks about the physics of water slides.
- SpaceX’s reusable Grasshopper rocket has set a new altitude test of over 1000 ft. Check out this feat of aerodynamic control over at io9.
- Stanford engineers are using high-speed video of birds in the wild to study the mechanics of flapping flight. If you check out their video, you’ll notice how the birds rotate their wings as they flap in order to maximize lift throughout the flapping cycle. (via io9)
- Speaking of io9, they highlighted a couple of great examples of meteorological fluid dynamics recently: roll clouds and water spouts.
- New research suggests that thresher sharks may whip their tails quickly enough to produce cavitation-induced shockwaves to stun their prey. If so, they join the pistol and mantis shrimp in utilizing this technique for hunting.
- If you’re looking for some casual games, Liquid Sketch is a fun fluids puzzle game for iOS (submitted by Keri B)
- Finally, congratulations to Toronoto’s AeroVelo for capturing the AHS Sikorsky Prize with their human-powered helicopter. Check out this video from their historic flight (submitted by Chris R).
(Photo credit: AeroVelo)


