Tag: sneezing

Simulating a Sneeze
Sneezing and coughing can spread pathogens both through large droplets and through tiny, airborne aerosols. Understanding how the nasal cavity shapes the aerosol cloud a sneeze produces is critical to understanding and predicting how viruses could spread. Toward that end, researchers built a “sneeze simulator” based on the upper respiratory system’s geometry. With their simulator, the team mimicked violent exhalations both with the nostrils open and closed — to see how that changed the shape of the aerosol cloud produced.
The researchers found that closed nostrils produced a cloud that moved away along a 18 degree downward tilt, whereas an open-nostril cloud followed a 30-degree downward slope. That means having the nostrils open reduces the horizontal spread of a cloud while increasing its vertical spread. Depending on the background flow that will affect which parts of a cloud get spread to people nearby. (Image and research credit: N. Catalán et al.; via Physics World)
Fediverse Reactions
April 1, 2025
Imitating a Cough
Coughing and sneezing create violent air flows in and around our bodies. As that fast air rushes over mucus layers in our lungs, throat, and sinuses, the resulting flow breaks up the mucus into droplets. To explore the details of that process, researchers built a “cough machine” that sends a rush of air over a thin film of water mixed with glycerol. The setup allows them to observe the physics in a way that’s nearly impossible in a human cough or sneeze.
Imitating a cough: high-speed video shows how a thin film made of water and glycerol breaks down in a strong airflow. Parts of the film inflate into hollow bags that form thinner weak spots. When the film breaks in those places, it forms rims and ligaments that create a spray of droplets.
As seen above, air flowing past shears the viscous fluid, stretching it out. The leading edge of the film destabilizes and breaks into large drops, but it’s what comes next that really gets things going. Areas of the film inflate to form hollow bags. When sections of the bag thin to about 1 micron, the film ruptures and the bags burst. This triggers a cascade of instabilities in the film’s rim that ultimately rip the film into a spray of tiny aerosol droplets. The researchers found that, despite their tiny size, these droplets collectively carry a large volume of liquid, making them all the more important for understanding transmission of respiratory illnesses. (Image credit: top – A. Piacquadio, experiment – P. Kant et al.; research credit: P. Kant et al.)
November 8, 2023
Slow Motion Speech
Sneezing, coughing, and speaking all produce a spray of droplets capable of spreading COVID-19 and other respiratory illnesses. This Slow Mo Guys video is the latest demonstration in a long line of evidence for why wearing masks in public is such an important part of ending our current public health crisis. Also, I think we can all agree: that sneeze footage is gross. (Image and video credit: The Slow Mo Guys)
November 25, 2020
Fluid Dynamics and Disease Transmission
Right now people around the world are experiencing daily disruptions as a result of the recently declared coronavirus pandemic. There is a lot we don’t know yet about coronavirus, though researchers are working around the clock to report new information. Today’s video, though a couple years old, focuses on an area of medical knowledge that’s historically lacking but extremely relevant to our current situation: the mechanics behind disease transmission through sneezing or coughing.
Lydia Bourouiba is a leader in this area of research. Her studies have focused not on the size range of droplets produced but on the dynamics of the turbulent clouds that carry these droplets and what allows them to persist and spread. If you’ve wondered just why healthcare providers are recommending masks for sick people, keeping large distances between individuals, and frequent hand-washing, the image above hopefully helps explain why. Droplets carried in these turbulent clouds can travel several meters, and the buoyancy of the cloud’s gas components can help lift droplets toward ceiling ventilation. Right now, social distancing is one of our best tools against this disease transmission.
My goal in posting this is not to panic anyone. Rather, I hope you leave better informed as to why these precautions are needed. With coronavirus, our detailed knowledge of its characteristics — how long it remains viable in the air or on surfaces, how much is needed for an infection to take hold, etc. — is limited. But from research like Bourouiba’s, we know that coughing and sneezing are remarkably efficient ways to deliver respiratory pathogens, and that’s why caution is warranted. Stay safe, readers. (Video credit: TEDMED; image credit: Bourouiba Research Group, source; research credit: L. Bourouiba et al., see also S. Poulain and L. Bourouiba, pdf)
March 16, 2020
Fish, Feathers, and Phlegm
Inside Science has a new documentary all about fluid dynamics! It features interviews with five researchers about current work ranging from the physics of surfing to the spreading of diseases. Penguins, sharks, archer fish, 3D printing, and influenza all make an appearance (seriously, fluid dynamics has everything, guys). If you’d like to learn more about some of these topics, I’ve touched on several of them before, including icing, penguin physics, shark skin, archer fish, and disease transmission via droplets. (Video credit: Inside Science/AIP)
September 27, 2016
Fluids Round-up
Last week was supposed to have a fluids round-up, but we were having too much fun walking on water instead. So here it is now!
– NASA has asked Congress for funding for new X-plane programs to explore solutions for greener airliners and quieter sonic booms to enable next-generation air travel. Popular Science, Gizmodo, and Ars Technica take a closer look at the proposed projects. I won’t lie – as an aerospace engineer I am hugely in favor of this. The first ‘A’ in NASA has been neglected for quite a while and projects like these are needed if we want to advance the state-of-the-art in aeronautics.
– The New York Times’ ScienceTake video series took a look back at their most popular videos, and 3 of the top 5 videos are fluid dynamics-related. Because we are just that awesome. (via Rebecca M)
– I made a guest appearance on last week’s Improbable Research podcast, where we talked about bizarre experiments trying to unravel swimming.
– Physics Girl shows us 5 weird ways to blow out a candle. There’s some neat and potentially non-intuitive fluid dynamics involved!
– SciShow offers an explanation of why we sneeze. Spoiler alert: it’s more than just to get rid of irritants.
– Fluid dynamics made the short list for NPR’s Golden Mole awards with the discovery of dancing droplets. Here’s Skunkbear’s take on it.
– Ernst Mach, of Mach number fame, was also a bit of an artist and philosopher. (via @JenLucPiquant)
– It’s not quite fluid dynamics, but this Slow Mo Guys video of spinning burning steel wool might be their most beautiful video yet. Check it out!
(Image credit: NASA)
March 10, 2016
Watching a Sneeze
What does a sneeze look like? You might imagine it as a violent burst of air and a cloud of tiny droplets. But this high-speed video shows, that’s only part of the story. The liquid leaving a sneezer’s mouth and nose is a mixture of saliva and mucus, and in the few hundred milliseconds it takes to expel this air/mucosaliva mixture, there’s not enough time for the liquid to break into droplets. Instead, liquid leaves the mouth as a fluid sheet that breaks into long ligaments.
Because mucosaliva is viscoelastic and non-Newtonian, it does not break down into droplets as quickly as water. Instead, when stretched, the proteins inside the fluid tend to pull back, causing large droplets to form with skinny strands between them – the beads-on-a-string instability. The end result when the ligaments do finally break is more large droplets than one would expect from a fluid like water. Understanding this break-up process and the final distribution of droplet sizes is vital for better understanding the spread of diseases and pathogens. (Video credit: Bourouiba Research Group; research paper: B. Scharfman et al., PDF)
February 25, 2016
The Physics of Sneezing
Sneezing can be a major factor in the spread of some illnesses. Not only does sneezing spew out a cloud of tiny pathogen-bearing droplets, but it also releases a warm, moist jet of air. Flows like this that combine both liquid and gas phases are called multiphase flows, and they can be a challenge to study because of the interactions between the phases. For example, the buoyancy of the air jet helps keep smaller droplets aloft, allowing them to travel further or even get picked up and spread by environmental systems. Researchers hope that studying the fluid dynamics and mathematics of these turbulent multiphase clouds will help predict and control the spread of pathogens. Check out the Bourouiba research group for more. (Video credit: Science Friday)
September 8, 2014
Sneezes Vs. Coughs
Sneezing and coughing are major contributors to the spread of many pathogens. Both are multiphase flows, consisting of both liquid droplets and gaseous vapors that interact. The image on the left shows a sneeze cloud as a turbulent plume. The kink in the cloud shows that plume is buoyant, which helps it remain aloft. The right image shows trajectories for some of the larger droplets ejected in a sneeze. Like the sneeze cloud, these droplets persist for significant distances. The buoyancy of the cloud also helps keep aloft some of the smaller pathogen-bearing droplets. Researchers are building models for these multiphase flows and their interactions to better predict and counter the spread of such airborne pathogens. For similar examples of fluid dynamics in public health, see what coughing looks like, how hospital toilets may spread pathogens, and how adjusting viscoelastic properties may counter these effects. For more about this work, see the Bourouiba research group’s website. (Image credit: L. Bourouiba et al.)
March 27, 2014