The schlieren photographic technique is often used to visualize shock waves and other strong but invisible flows. But a sensitive set-up can show much weaker changes in density and pressure. Here, schlieren is used to show the standing sound wave used in ultrasonic levitation. By placing the glass plate at precisely the right distance relative to a speaker, you can reflect the sound wave back on itself in a standing wave, seen here as light and dark bands. The light bands mark the high-pressure nodes, where the pressure generated by the sound waves is large enough to counteract the force of gravity on small styrofoam balls. This allows them to levitate but only in the thin bands seen in the schlieren. Move the plate and the standing wave will be disrupted, causing the bands to fade out and the balls to fall. (Video and image credit: Harvard Natural Sciences Lecture Demonstrations)
Recurring slope lineae (RSL) are seasonal features on Mars that leave behind gullies similar to those left by running water on Earth. Their discovery a few years ago has prompted many experiments at Martian conditions to determine how these features form. At Martian surface pressures and temperatures, it’s not unusual for water to boil. And that boiling, as some experiments have shown, introduces opportunities for new transport mechanisms.
Researchers found that water in “warm” (T = 288 K) sand boils vigorously, ejecting sand particles and creating larger pellets of saturated sand. Water continues boiling out of the pellets once they form, creating a layer of vapor that helps levitate them as they flow downslope. The effect is similar to the Leidenfrost effect with drops of water sliding on a hot skillet; there’s little friction between the pellet and the surface, allowing it to travel farther.
The mechanism is quite efficient in experiments under Earth gravity and would be even more so under Mars’ lower gravity. It also requires less water than alternative explanations. The pellets that form are too small to be seen by the satellites we have imaging Mars, but the tracks they leave behind are similar to the RSL seen above. (Image credit: NASA; research credit: J. Raack et al., 1, 2; via R. Anderson; submitted by jpshoer)
5 Reasons Why Astronomy Is Better From The Ground Than In Space
“5.) On Earth, you can observe from anywhere you want. Once your observatory goes to space, gravity and the laws of motion fix, at any given time, exactly where that spacecraft is going to be. Plenty of astronomical curiosities can be seen from everywhere, but there are some spectacular events that require you to be in a very specific location at a particular moment in time. Occultations are an extreme example of this, where a distant, small object in the Solar System passes in front of a background star, but only for a brief instant in a particular location. Neptune’s moon Triton and New Horizons’ first post-Pluto destination, MU69, both occulted background stars, with Triton doing so regularly. Space telescopes have never been lucky enough to catch these, but thanks to mobile observatories like NASA’s SOFIA, we’ve learned how Triton’s atmosphere changes with its seasons, and we’ve even discovered a small moon around MU69! Because we don’t put all our eggs in the telescopes-in-space basket, we can do the unique science that the light arriving at our world enables.”
When it comes to astronomy, space telescopes get all the love. By flying above the atmosphere, there’s no need to wait until the atmospheric and day/night conditions are right to observe; you can look at whatever you want pretty much whenever you want, and for as long as you want. You don’t have to contend with clouds or atmospheric turbulence, and the entire electromagnetic spectrum is available to look at. We normally think of these advantages, but we hardly ever think about how much worse many things are in astronomy from space. But there are legitimately huge advantages to being on the ground, and cost doesn’t even need to be a factor to come up with five tremendous ones!
The Slow Mo Guys have a history of personal sacrifice in the name of cool high-speed footage, and their Super Slow Show is no exception. In a recent segment, both Dan and Gav were knocked flat by giant swinging balloons of paint, and, as you might expect, the splashes are spectacular. The speed is just right for some of the paint to form nice sheets before momentum pulls them into long ligaments. Eventually, that momentum overcomes surface tension’s ability to keep the paint together, and the paint separates into droplets, which, as you see below, rain down on the hapless victims. (Video and image credit: The Slow Mo Guys)
Dispersing seeds is a challenge when you’re stuck in one spot, but plants have evolved all sorts of mechanisms for it. Some rely on animals to carry their offspring away, others create their own vortex rings. The hairyflower wild petunia turns its fruit into a catapult. As the fruit dries out, layers inside it shrink, building up strain that bends the fruit outward. Once a raindrop strikes it, the pod bursts open, flinging out around twenty tiny, spinning, disk-shaped seeds. That spin is important for flight. The best-launched seeds may spin as quickly as 1600 times in a second, which helps stabilize them in a vertical orientation that minimizes their frontal area and reduces their drag. Researchers found that these vertically spinning seeds have almost half the drag force of a spherical seed of equal volume and density. That means the hairyflower wild petunia is able to spread its seeds much further without a larger investment in seed growth. (Image and research credit: E. Cooper et al., source; via NYTimes; submitted by Kam-Yung Soh)
Our adventures with pressure continue after the trip to the aquarium. To see just how much pressure we could generate with height, A.J. and I teamed up with the Corvallis Fire Department to recreate an experiment attributed to 17th-century French physicist Blaise Pascal. In Pascal’s experiment, he (supposedly) used a column of water to burst a wooden barrel. In ours, we use a ladder truck to make a 30-meter column of water burst a glass carboy! We also got a little help from our friends at the Lutetium Project to introduce you to Pascal and his work. (Thanks, Guillaume!) We’ll tell you more about Pascal and his contributions in an upcoming video, so stay tuned. (Video and image credit: A. Fillo and N. Sharp)
You might have seen animations like this that show an electron undergoing a transition from a lower energy to a higher energy state and vice versa like so:
There is something really important about this image that one must understand clearly.
The diagram represents the transition in energy of an electron BUT this does not mean that the electron
is magically jumping from one position and respawning at another
The electron’s position is NOT doing this i
If you want to know about the probability of finding an electron around the nucleus at a certain energy level, you look at its wavefunction and not at the energy diagram.
Here is the wavefunction of a hydrogen atom and each stationary state defines a specific energy
level of the atom.
This might not sound like a big deal but one might be surprised to know that there are a lot of people who think that the electron is magically transported from energy level to another which most certainly is not true.
Pressure is a concept that can be unintuitive, but it’s incredibly important in physics and engineering. So I’m excited to debut a collaborative video series that @mostlyenginerd and I are producing all about hydrostatic pressure! Today’s video is one of our openers: it focuses on where pressure comes from and why it’s a function of height but not volume. And to show you just how pressure increases with depth, we teamed up with divers from the Oregon State University Scientific Diving Team and headed to the Oregon Coast Aquarium’s Halibut Flats exhibit. Ever seen what a balloon looks like 7 meters underwater? You’re about to! (Video and image credit: N. Sharp and A. Fillo)
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