Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
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Bottle Rocket Shock Diamonds
Mach diamonds or shock diamonds can often be seen in the exhaust of rocket engines. Here they’re shown in high-speed video of a bottle rocket’s launch. The rocket’s exhaust exits at a pressure that is higher than the surrounding atmosphere, which causes the exhaust to bulge outward and forms two expansion fans, seen in pink,…
Titan’s Bubbly Islands
Titan, Saturn’s largest moon, is a fascinating world with remarkable similarities to our own. It is the only other world we know of with stable bodies of liquid at its surface. Unlike Earth, frigid Titan’s lakes and seas are filled with methane and ethane. Radar data from the Cassini mission has shown oddly changing shorelines…
Reader Question: Image Credits
kermitsstickylittlefingers asks: Dear Nicole, thanks a lot for your amazing blog which I have been following for years. My name is Julian and I am a PhD candidate working on tree frog attachment at Wageningen University in the Netherlands. Inspired by FYFD, I decided to start a science blog on bioadhesion and biomimetics. With respect to…
Hot Versus Cold
Did you know that you can hear the difference between hot and cold water when they’re poured? Go ahead and give the video above a listen to try it out. I’ll wait. As explained in the video, the viscosity of water changes with temperature – the higher the temperature, the lower the viscosity. In fact,…
Surface Tension’s Pop
Surface tension in a liquid arises from molecular forces. Within a liquid like water, a molecule inside the fluid experiences equal tugs from similar molecules in every direction. A molecule at the surface, on the other hand, experiences the pull of similar molecules only on some sides. The net effect of this imbalance is a…
Sloshing in Space
Last month, French astronaut Thomas Pesquet posted a video of some experiments he did on the International Space Station exploring the movement of fluids in microgravity. He filmed the experiments as part of the SPHERES Slosh project. Sloshing is the technical term for how liquids respond to the motion of their container, and it’s a…
Breaking Down Vortices
Vortex rings are ubiquitous in nature, showing up in droplet impacts, in propulsion, and even in volcanic eruptions. Understanding the interaction and breakdown of multiple vortices with one another is therefore key. The image above shows a circular disk that’s being oscillated up and down (in and out of the page). As the disk moves…
Molten Copper
In this video, the Slow Mo Guys prove that pouring molten copper in slow motion is every bit as satisfying as one would imagine. Because they pour the metal from fairly high up, they get a nice break-up from a jet into a series of droplets; that’s due to the Plateau-Rayleigh instability, in which surface…
Shocks on a Wing
Commercial airliners fly in what is known as the transonic regime at Mach numbers between 0.8 and 1.0. While the airplane itself never exceeds the speed of sound, that doesn’t mean that there aren’t localized regions where air flows over the airplane at speeds above Mach 1. In fact, it’s actually possible sometimes to see…
Vertical Axis Wind Turbines
Most people are familiar with the propeller-like shape of conventional wind turbines. These turbines can be more than 100m tall and can generate several megawatts apiece, but placing them in arrays requires a lot of open space because flow downstream of one turbine will interfere with the efficiency of the next. Vertical axis wind turbines…