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YouTube / Jefferson Lab
YouTube / Jefferson Lab

Can of Soda vs. Liquid Nitrogen

YouTube / Jefferson Lab
YouTube / Jefferson Lab

What happens when you put a can of soda* in liquid nitrogen? Well, we can predict that it will freeze, but how? Let's hope it's catastrophic:

Incidentally, I'm in the middle of reading the new Neal Stephenson book Seveneves, and am reminded of this passage:

"[The spacecraft] were just big aluminum cans with domes welded onto the ends. The walls of the can had a thickness of about a millimeter. The domes were a bit sturdier. The thickest and strongest parts of the hull were in the places where the domes overlapped the ends of the can. The analogy was to a plastic soda bottle, whose thin walls could be crumpled in one hand when the lid was off, but which became amazingly stiff and strong when it was pressurized. Or at least that was what NASA was saying to people who were alarmed by the idea of living one millimeter away from the vacuum of space."

Stephenson, Neal (2015-05-19). Seveneves: A Novel (pp. 197-198). HarperCollins. Kindle Edition.

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* = Pop, soft drink, fizzy drink, carbonated liquid, "Coke," etc.

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science
Researchers Pore Over the Physics Behind the Layered Latte
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iStock

The layered latte isn't the most widely known espresso drink on coffee-shop menus, but it is a scientific curiosity. Instead of a traditional latte, where steamed milk is poured into a shot (or several) of espresso, the layered latte is made by pouring the espresso into a glass of hot milk. The result is an Instagram-friendly drink that features a gradient of milky coffee colors from pure white on the bottom to dark brown on the top. The effect is odd enough that Princeton University researchers decided to explore the fluid dynamics that make it happen, as The New York Times reports.

In a new study in Nature Communications, Princeton engineering professor Howard Stone and his team explore just what creates the distinct horizontal layers pattern of layered latte. To find out, they injected warm, dyed water into a tank filled with warm salt water, mimicking the process of pouring low-density espresso into higher-density steamed milk.

Four different images of a latte forming layers over time
Xue et al., Nature Communications (2017)

According to the study, the layered look of the latte forms over the course of minutes, and can last for "tens of minutes, or even several hours" if the drink isn't stirred. When the espresso-like dyed water was injected into the salt brine, the downward jet of the dyed water floated up to the top of the tank, because the buoyant force of the low-density liquid encountering the higher-density brine forced it upward. The layers become more visible when the hot drink cools down.

The New York Times explains it succinctly:

When the liquids try to mix, layered patterns form as gradients in temperature cause a portion of the liquid to heat up, become lighter and rise, while another, denser portion sinks. This gives rise to convection cells that trap mixtures of similar densities within layers.

This structure can withstand gentle movement, such as a light stirring or sipping, and can stay stable for as long as a day or more. The layers don't disappear until the liquids cool down to room temperature.

But before you go trying to experiment with layering your own lattes, know that it can be trickier than the study—which refers to the process as "haphazardly pouring espresso into a glass of warm milk"—makes it sound. You may need to experiment several times with the speed and height of your pour and the ratio of espresso to milk before you get the look just right.

[h/t The New York Times]

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Kirill Ignatyev, Flickr // CC BY-NC 2.0
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Why Some Cold Cuts Make Iridescent Meat Rainbows—and Why They're Still OK to Eat
Kirill Ignatyev, Flickr // CC BY-NC 2.0
Kirill Ignatyev, Flickr // CC BY-NC 2.0

We eat with our eyes first, and sometimes what we see on our plate turns us off a meal altogether. Take so-called “meat rainbows”: They happen when a slice of deli meat takes on an iridescent shimmer reminiscent of an oil puddle in a parking lot—a.k.a. not something you want on your sandwich. Despite giving a whole new meaning to the phrase "mystery meat," the odd discoloration is perfectly safe to eat, as physicist Dave McCowan at the University of Chicago explained for The Takeout.

The colorful sheen on a slice of roast beef or pastrami isn’t a sign of spoilage or chemical additives—it’s actually a result of the way the meat is cut. Slicing meat “against the grain” means cutting through, rather than parallel to, the bundles of fibers composing the meat’s musculature. This makes for a more tender bite, and it also leaves a grid of evenly-spaced meat fibers. In the right light, this surface lends itself to something called “diffraction.”

Diffraction occurs when light hits a repeating pattern of nooks and crannies. As the white light bounces off the grooves in the meat, it separates into a spectrum of distinct colors. Some of these colors are amplified, creating a mother-of-pearl appearance when viewed together. This is the same effect we see on the backs of CDs and DVDs.

Another possible culprit behind your rainbow meat is thin-film interference. This is sometimes present in meat with a thin layer of oily fat on the surface. The film affects the light passing through it in such a way that only some of the colors in the spectrum come through, hence the rainbow. This phenomenon produces a sheen closer to that of bubbles or oil slicks than laser discs.

Why do meat rainbows only seem to show up in deli slices, not raw cuts? The answer lies in the curing process. A cured ham is likely greasier than a raw pork cutlet, which makes thin-film interference more likely. The muscle fibers in cured and cooked meats are also more tightly packed together, producing the rigid grid necessary for diffraction.

Color also plays a role. Iridescent shimmers are easier to spot on darker meats like beef and some pork—so if you’re eating a slice of turkey from the deli, it could be covered in meat rainbows you don’t notice. We’ll let you decide if that’s a positive thing.

[h/t The Takeout]

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