There is a remarkable amount of physics contained in art. In this video, scientists from The Splash Lab explore some of the physics involved in pouring paint atop a rectangular post. The spreading paint transforms its shape repeatedly, and, at the corners of the post, it preserves a tiny history of all the colors poured. Paint sliding down the sides shifts from a thin sheet to a thicker jet that deposits color in waves. For tall posts, the distance the paint falls is long enough for instabilities to set in, producing a paint puddle that’s riddled with curves and waves between each color of paint. It’s a lovely reminder of the complexity inherent even within a simple action. (Video credit: R. Hurd et al.)
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The Sound of a Balloon Popping
The pop of an overfilled balloon is enough to make anyone jump, but you’ve probably never seen it like this. The photo above uses an optical technique known as schlieren photography that reveals changes in density of a transparent gas like air. The shredded rubber of the balloon is still visible in black, and around the balloon there’s an expanding spherical shock wave. It’s the sudden release of energy when the balloon ruptures and the gas inside begins to expand that causes the shock wave. Notice, though, that the gas from the balloon is still clearly visible and balloon-shaped–much like a water balloon that’s just popped. From that clear delineation, I would say that this balloon was filled with a different gas than air–otherwise the density shouldn’t be different enough to make the interior gas distinguishable. (Image credit: G. Settles)
Inside Cavitation
Cavitation bubbles live a short and violent life. It begins when a low-pressure void forms in a fluid–for example, when a liquid is accelerated so that the pressure drops below the vapor pressure, which can happen at the tips of a boat’s propeller or when striking a bottle. The bubbles that form expand and then collapse rapidly as the higher pressure of the liquid surrounding them squeezes them down. That collapse of the bubble is so violent that it heats the fluid inside the bubble to temperatures hotter than the surface of the sun, generating both a flash of light and a shock wave. It’s these shock waves that cause much of the damage associated with cavitation in engineering, but they can be used for good as well. Shock wave lithotripsy uses cavitation-induced shock waves to break down kidney stones. (Image credit: O. Supponen et al., source)
Swirling Pollen
This photo captures the chaotic mixing present in a simple puddle. Pine pollen strewn across the puddle’s surface acts as tracer particles, revealing some of the motion of the underlying water. As wind blows across the puddle, it moves the water through the formation of ripples and by shearing the surface. That deformation on the top of the puddle will cause further motion beneath the surface. With time and changing wind direction, the resulting pattern of flow can be very complex! (Photo credit: K. Jensen, original)
Pelican Surfing
Birds can be incredibly clever about using their surroundings to enhance their flight. Pelicans will even surf! As a line of waves rolls toward shore, it pushes a small updraft ahead of it – just like a line of mountains creates a windy updraft. Pelicans save energy by riding the updraft just like a surfer would ride the swell. Once the wave breaks, the air and water become turbulent and less useful, so the pelican cuts away to find his next ride. (Image and submission credit: N. Yarvin, source)
Inside a Supernova
During a supernova, shock waves moving outward push denser material into less dense plasma and gas. This causes what is known as a Richtmyer–Meshkov instability, where the interface between the two fluids first becomes wavy and then develops finger-like intrusions. Those too break down, as seen in the simulation above, causing large-scale mixing between the different fluids.
Here on Earth this instability shows up in the process of inertial confinement fusion. In that case, the outer shell material is denser than the fuel core and the instability is triggered during the implosion process. As the fusion material is suddenly compressed, waviness and mixing occurs along the interface between the shell and the fuel. That’s undesirable because it reduces the efficiency of the fusion reaction. (Image credit: E. Evangelista et al.)
Ionic Sound
So, as we learned previously, sound can actually travel through space. But the recordings our spacecraft send us from other planets or from the edge of the Solar System aren’t really that kind of sound. Acoustic waves require a medium; they travel when particles bump into one another, which, given the sparseness of space, means that only very low frequency sounds can travel. But space has a lot of ions and plasmas – charged particles like electrons and protons – and those particles can interact without physically contacting one another. Instead their motion causes a changing magnetic field that affects nearby particles, which in turn affect more particles (and so on). This transmits what’s called ionic sound. Check out the video above to hear some awesome examples of the ionic sounds of our solar system! (Video credit: The Point Studios)
Shark Tooth Instability
Imagine that you partially fill a horizontal cylinder with a viscous fluid, like corn syrup or honey. If that cylinder is still, the fluid will simply pool along the bottom. On the opposite extreme, if you spin it very fast, that cylinder will become coated in an even layer of fluid that rotates along with the cylinder thanks to centrifugal force. Between those two extremes in rotational velocity, some interesting fluid behaviors occur. Start spinning the cylinder and some of the pooled fluid will be pulled up the sides, eventually forming a thicker film with a straight front along the bottom of the cylinder. Spin faster and that straight front starts to break down, forming sharper cusp-like waves known as shark teeth. (Image credit: S. Morris et al., source; research credit: S. Thoroddsen and L. Mahadevan)
Shear Across the Water
This photo series shows the development of a Kelvin-Helmholtz instability. It’s formed when two layers of fluid move past one another at different speeds. In this case, the two fluids meet off the back of a flat plate (seen at the left of the top image) when fast-moving flow from the top of the plate encounters slower fluid beneath. Friction and shear between the fluid layers causes billows to rise up and form waves very similar to those on the ocean (wind across the water works the same way!). Those waves turn over into vortex-like spirals and keep mixing until they break down into turbulence. This pattern crops up pretty frequently, especially in clouds. (Image credit: G. Lawrence)
Bioluminescent Shrimp
Trevor Williams and Jonathan Galione of Tdub Photo captured these beautiful images of bioluminescent shrimp along the Japanese coast. The duo collected the tiny shrimp and poured them over and near rocks to create the effect they wanted. With their blue light, the shrimp act like tracer particles in the water, and with long exposures, the photos track the movements of the shrimp and waves. Technically speaking, they trace out pathlines – the trajectory that a specific fluid (or shrimp) particle takes in a flow. It’s a lovely way of capturing the water’s dynamic motion in a still photo. (Image credit: Tdub Photo; via Colossal)