Tag: physics

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)
September 5, 2016
Where Does the Sun End?
How do you define the edge of our sun? There’s a distinct surface to it, but our star is also surrounded by the corona, an even hotter region of plasma twisted by magnetic fields. The corona is sort of like the sun’s atmosphere. Farther out in the solar system, we receive a constant barrage of charged particles, known as the solar wind, that streams out from the sun. So where does the corona end and the solar wind begin?
Scientists have been studying the flow structure of the solar wind in search of an answer to this question, and they’ve found that there’s a clear transition point about 32 million kilometers from the sun. At this distance, the sun’s magnetic field weakens to the point where it no longer exerts the same hold on the solar particles and they begin to move turbulently, behaving more like a gas than a plasma. With special measurements and image processing, scientists were able to actually see this flow change in the solar wind! (Video/image credit: NASA; research credit: C. DeForest et al.; via FlowViz)
September 2, 2016
Microburst
Earlier this week a Columbus, OH TV station tower camera caught this awesome timelapse footage of several microbursts in a thunderstorm. A microburst is a sudden, localized downdraft inside the storm. You can see a clear microburst starting at about 0:30 seconds. Note how it flares up and out as it hits the ground, eventually settling around the time a rainbow appears on the left edge of the frame. These strong winds moving down then curling out can be dangerous, both to structures on the ground and to any aircraft unfortunate enough to be taking off or landing in the storm. (Video credit: WCMH; submitted by
A. Bcstractor)
September 1, 2016
Leidenfrost Atop Gasoline
The animations above show a little of what happens when you pour a spoonful of liquid nitrogen onto a container of gasoline. A couple of things are happening simultaneously here. First of all, the liquid nitrogen is experiencing the Leidenfrost effect. Because of the extreme difference in temperature between the gasoline (~20 degrees C) and the liquid nitrogen (-196 degrees C), part of the nitrogen is evaporating immediately, creating a vapor layer that insulates the remainder of the liquid nitrogen and allows it to float above the gasoline surface. The same thing happens to water drops on a very hot skillet.
The extreme cold of the nitrogen also seems to have formed some ice that’s further protecting the nitrogen drop. I’m not 100% sure what that would be made of, though – a mixture of water and gasoline?
Finally, there’s the simultaneous evaporation of the liquid nitrogen and the sublimation of the ice. This is the white vapor we see propelling and spinning the ice/drop. Note the “bounce” that happens in the top animation. The drop never actually impacts the wall. When it gets close, the escaping vapors are affected by the wall and start pushing the drop in a new direction! Check out the whole video below. (Image credit: carsandwater; via Gizmodo)
August 31, 2016
Making Droplets Stick
Lots of plants have evolved leaves that are superhydrophobic – that is, water repellent. For a plant, this makes a lot of sense. A superhydrophobic leaf will make water bounce and run off, draining down to where the plants roots can drink it up. But this same feature can be a frustration to farmers who spread pesticides by spraying plants. They need the pesticide to stick to the leaves if it’s to deter insects, and the superhydrophobicity of the leaves forces them to spray more pesticides in the hopes of getting some to stick. Researchers at MIT are looking to change this status quo with a few biodegradable polymer additives that can counter the leaves’ superhydrophobic tendencies and help droplets stick to the surface. This could reduce the amount of pesticides needed to protect crops. (Video credit: MIT)
August 30, 2016
Gunshot Back-Splatter
Today blood pattern analysis is an important forensic technique used in reconstructing the events at crime scenes. Many methods use straight-line trajectories to try to isolate the origin of blood splatters, but this discounts the effects of gravity and drag on flying droplets. A new theory models the back-splatter of a gunshot wound fluid dynamically.
Using characteristics of the bullet and gunshot, it estimates the initial conditions of blood drops leaving a wound, then models the break-up of the fluid as a Rayleigh-Taylor instability, where a denser fluid (blood) is accelerating into a less dense fluid (air). This results in a moving cloud of droplets and air whose trajectory and impact on a surface can be calculated. The ultimate goal is to create a physical model that can be used in reverse, where analysts can observe patterns and calculate their origin with confidence. For more, see the original paper or Gizmodo’s coverage. (Image credit: T. Webster; research credit: P. Comiskey et al.)
August 29, 2016
Where Jupiter’s Heat Comes From
Exactly what goes on in Jupiter’s atmosphere has confounded scientists for decades. Its upper atmosphere – essentially the only part we can observe – is hundreds of degrees warmer than solar heating can account for. Although it has bright auroras at its poles, that energy is trapped at high altitudes by the same rotational effects that create Jupiter’s stunning bands.
Observations of Jupiter’s Great Red Spot, a storm that’s lasted for hundreds of years, may provide clues as to where all the extra heat is coming from. Spectral mapping shows that the area over the Spot is over 1000K warmer than the rest of the upper atmosphere. Because of its isolated location, the best explanation for the Great Red Spot’s extra heat comes from below: scientists suspect that the raging storm is generating so much turbulence and such a deafening roar that these gravity and acoustic waves propagate upward and heat the atmosphere above. If so, a similar coupling mechanism to the clouds below may account for the widespread warmth in Jupiter’s upper atmosphere. (Image credit: NASA; research credit: J. O’Donoghue et al.)
August 26, 2016
Quantum Droplets
Over the past decade, fluid dynamicists have been investigating tiny droplets bouncing on a vibrating fluid. This seemingly simple experiment has remarkable depth, including the ability to recreate quantum behaviors in a classical system. In this video, some of the researchers demonstrate their experimental techniques, including how they vary the frame rate relative to the bouncing of the drops. At the right frame rate, this sampling makes the droplets appear to glide along with their ripples, giving us a look at a system that is simultaneously a particle (drop) and wave (ripple). (Video credit: D. Harris et al.)
August 25, 2016
How Many Licks Does It Take to Get to the Center of a Lollipop?
Many a child has wondered how many licks it takes to get to the center of a lollipop. Physically, this is a problem of a solid body dissolving in a flow, and it’s one scientists are interested in for its geological, industrial, and pharmacological applications.
The animation above shows flow around a dissolving (candy!) body that was originally spherical. With both spheres and cylinders, the final shape the body takes is consistent – it has a front boundary with a curvature of nearly constant radius and a back face that is approximately flat. This creates a boundary layer of uniform thickness across the front face, and that uniform flow makes the surface dissolve steadily and evenly so that it maintains the same overall shape.
With their model and experiments, researchers have even been able to tackle the classic question of how many licks it takes:
“For candy of size 1 cm licked at a speed of 1 cm/s, we estimate a total of 1000 licks, a prediction that is notoriously difficult to test experimentally.”
(Image credit: J. Huang et al., source, pdf)
August 24, 2016
Capturing SLS
NASA’s recent full-scale ground test of their Space Launch System (SLS) rocket was notable for more than just the engine. It was an opportunity to use a new high dynamic range, high speed camera prototype,
HiDyRS-X, to capture the rocket’s exhaust in detail never seen before. Usually the extreme brightness of the rocket exhaust makes it impossible to see any structure in the flow without completely obscuring the ground equipment. With this camera, however, engineers can see how the engine, exhaust, and surroundings all interact. Be sure to check out the full video. I particularly like watching how the rocket’s exhaust entrains dust and sand from the ground nearby. (Image credit: NASA, source; submitted by Chris P. and Matt S.)
August 23, 2016