Knight -> Fox

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I missed last week, but now I’m back in the saddle today with an extra-long one.

A medieval knight in full armor was closer to overheating than freezing. A suit of armor is a metal box with as few large openings as possible, because every hole to let heat out could also let something sharp in. According to those who still wear armor today, that can be kind of nice in the cold. In the heat, though, it would have been miserable, combining trapped body heat with absorbed sunlight to make something decidedly uncomfortable. As one poster on that forum writes, “In warm weather, you just sweat profusely until everything is soaked.” Delightful.

Being a true white knight might have helped a little bit in direct sunlight, which would bounce off white armor instead of being absorbed by it. But white armor also wouldn’t radiate body heat away as effectively as darker armor would, so it would be better at keeping everything inside the armor (namely: You) at a constant temperature. That might make it something of a wash.

This effect is also entangled with a thorny issue within evolutionary biology: Countershading. Most animals have dark backs and light bellies (except a few who live life upside-down and have dark bellies and light backs). The common explanation of countershading goes back to Abbott Thayer taking pictures of dead birds and hypothesizing that countershading is for camouflage. (He actually proposed two related but distinct ideas that are popularly squashed together because people like simple stories). But experimental biologists have found that countershading doesn’t always help an animal camouflage—in one experiment, creating fake insects with lard and flour, countershading half of them, and seeing which were more readily eaten by birds.

Countershading doesn’t always help with camouflage, but it can help with movement. Dark backs absorb sunlight, heat up, and emit that heat back into their environment. That lowers the viscosity of the air or water around the animal and makes it easier to move through. Bellies are light because there’s no need to make pigment for an area that doesn’t get hit by sunlight anyway. This is just one of many effects of countershaded bodies, though, as I wrote about at greater length for this video.

Of course, the true answer, as in so many situations that are popularly presented as “this or that”, the answer is probably both: Countershading helps with camouflage in some cases and helps with other things in other cases. Besides, it can’t have nothing to do with camouflage, because one of the few places where animals aren’t countershaded are snow-covered, where dark backs would stand out. And that’s why arctic foxes, unlike their redder cousins, are adorably monochromatic.

Chin -> Penguin

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Chins are funny. Every human has one; no human knows why.

No other primate (extinct or extant) has a chin. Everyone else’s mouth curves inward at the bottom, making chins a curiously and uniquely human trait. There are a few popular ideas for why chins evolved, but none of them holds water. Or food. None of them holds whatever’s in your mouth like your trusty chin does. The proposals that say chins served an evolutionary purpose (whether mechanical or sexual) don’t hold up to scrutiny, while what seems like the best idea (that chins were simply exposed as our ancestors’ faces shrunk) is difficult to prove. It’s a chin-undrum. (That’s conundrum, but chin.)

All I know, really, is that when I’m outside in a blizzard, I need to keep my chin covered because of our old friend the square-cube law. Chins have a lot of surface area, so they lose heat quickly, but they only get warmed at the same rate as the rest of the body (which has less surface area compared to its volume than a chin does). Combine those and it means that chins, ears, fingers, toes, and noses lose heat faster than it’s supplied.

Emperor Penguins have learned the square-cube law, too; it’s why they huddle by the thousands through the Antarctic winter instead of letting every individual fend for themselves. Each member of the huddle has some of their body exposed to the wind and some exposed to other (warm) penguins. Less heat escapes to the wind than it would if everyone were alone. This shielding works so well, in fact, that the penguins at the center of the huddle can get too warm! They move away from the middle to cool off.

When they move to the edge, those on the edge get to shuffle their way toward the middle. They get to warm up and stay alive after bearing the brunt of the cold, the same way members of a household might rotate shoveling duty when it’s really cold outside so that no one gets frostbitten.

At least, that’s the hope—in both cases.

Yard -> Yacht

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What a consonant set of options to choose from today. I went with these two because we all know alliteration is the best literary device.

A yard is, by definition, exactly three feet. (That’s about a meter, more or less.) But “exactly three feet” is only helpful if you know how long a foot is, which historically wasn’t a given. So people would estimate a yard as the distance from their nose to their outstretched fingertips. (Of course, this meant different people had different “yards”, but generally they’d be close enough—unless you were buying from a giant. Then: Bonanza.) (Self-promotion time: If you’re really into units and measurements, I’ve scripted a number of videos about them.)

For me, one of the most interesting parts of all this is that, subjectively, stretching out an arm feels like pushing a hand away from our body—even though that’s not what happens. Our muscles can’t push on our bones; they can only pull on them. When you extend your arm, muscles in the back of your arm (your triceps) pull your forearm toward your elbow, swinging your hand away from your body as a result.

There’s a similar (for a very specific idea of “similar”) misconception that surrounds sails. People think they’re pushed by the wind (like bouncy castles), but that’s only true sometimes. If it were the only option, sailboats wouldn’t be able to go anywhere but downwind. To go upwind, though, sails act more like wings than anything else, propelling the ship below along more through lift than direct wind-on-sail impact. Sails are wings turned on their sides.

Skirting around the mechanics of lift for the second post in a row, this was just as true for the ships of the Spanish Armada as it is for today’s yachts.

At least, as long as those yachts have sails instead of motors. But motors are a story for another time, too.

Egg -> Ladybug

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Ladybugs hatch from eggs. We’re done here.

What’s that? The header picture says to go from egg to ladybug, not vice versa? Well, that will take longer, and there will be dragons bridges.

Eggs are only fragile when squeezed the wrong way. If you squeeze top-to-bottom rather than side-to-side, eggs are shockingly strong. Your average chicken egg can withstand 100 pounds. Your average ostrich egg, 1000. (Although I live in Massachusetts, where there is no such thing as an average ostrich. There is only, “Oh my god is that an ostrich? How is it so big? Why’s it in the living room?”)

Incredulity over the existence of ostriches aside, let’s return to incredulity about the strength of eggs. Force on the top gets spread through the rest of the shell, just like in an arched bridge. But it’s more interesting than that cursory summary suggests. Eggs and bridges don’t merely spread forces. they transform tension into compression. Tension spreads a material apart while compression squeezes it together. Most materials, including eggshells and concrete, are stronger under compression than tension, because little cracks get shoved together instead of being opened wider.

Most, but not all. It’s fairly hard to tear a piece of paper by pulling two sides apart (tension) but fairly easy to crumple it by pushing the sides together (compression). That also makes paper easy to fold into airplanes. (I never got into the paper airplanes with flat ends, even though they always seemed to work better. I’m something of a purist.) Now, planes fly for a constellation of reasons that are a story for another time. Insects, on the other hand, fly for reasons that are (mostly) a story for right now. They push their wings down against the air, which, through Newton’s Third Law, pushes them back up. That’s far from the full picture, of course. Air’s viscosity and other aspects of fluid dynamics mean that insect flight is in truth as complex as anything else. But that’s the big-picture gist for all insects.

Including, of course, ladybugs. Now we’re done here.

Blueprint -> Drip

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This is one where any pair would have been fun to dive into. But I’ve been programming a lot recently, so blueprint it is.

Blueprints are plans, originally for buildings but now metaphorically for just about anything. Real architectural blueprints, though, are always at a certain scale—dimensions are 1/10 the length they’ll be in the final building, say. And that scale is critical. the strength of a material goes up with its cross-sectional area (the square of its length) while weight increases with volume (the cube of length). This critical relationship between squares and cubes is known, sensibly enough, as the square-cube law. It means materials get heavier faster than they get stronger. A building built 15 times larger than a 1/10-scale blueprint will collapse like a house of toothpicks.

This isn’t just about engineering, either. An elephant is not simply a large mouse. The square-cube law means that an elephant shrunk to inches long would have absurdly thick legs, while a mouse inflated to 20 feet long couldn’t stand. (In another consequence of the same law, the giant mouse would explode while the tiny elephant froze.) (Also, it helps us know how big dinosaurs were.) In a computer, of course, you can make materials and legs any strength, regardless of size. But too-small supports will look weird: You can’t have giant simulated animals walking on string-bean legs. Even giraffe legs are thicker than you might imagine.

Chaos is another tricky thing to do in a computer. Chaotic systems turn tiny changes at one moment into enormous divergences later on, and computers have to make small approximations all the time—whether that’s something like rounding 1/3 to 0.3 or breaking time into discrete moments. But on the other hand, the advent of fast computers was one reason chaos was discovered when and how it was: Chaotic systems are often much easier to study in a computer than experimentally, since experiments always have little uncertainties. This is why fluid dynamics is dominated by simulations.

I could say more about chaos and I’m sure I will eventually, but suffice to say for now that one of the early chaotic systems studied both experimentally and computationally, was, of course, a dripping faucet.

Also, I’m going to shamelessly plug the physics simulations and visualizations I’ve been building. Check them out!

Brendan’s Adventures in Python

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It would be a lie to say I’ve never done much programming, and I don’t like lying.

I learned bits and pieces of HTML in high school to customize my profile page (RIP Sodahead), and I learned some more in college to create a finding aid for one of my library jobs. I also dragged my feet and struggled to learn the fairly basic Mathematica required for physics classes.

But my main programming experience came from research. I used MATLAB to analyze data and create figures like this beauty:

Fun fact about me: I love this figure so much that my master’s thesis is dedicated to it.

More seriously—and more relevantly for this post—I found backdoor ways of making MATLAB do animations and displaying something like a movie, which it was most certainly not built to do.

Long story short: There’s a thing moving through fluid. We watched it with four high-speed cameras, built the object in a computer, and matched the one we built with the one on the cameras.

But that only went so far, and then I graduated and set it aside. In the last few years, if I needed an animation, I used PowerPoint.

Then, about two or three years ago, inspired in part by creators like 3Blue1Brown and the frequency with which Matt Parker says “Python” (that list of links took far too long to compile), I tried downloading Python to see what I could do with it. That experience was frustrating and unproductive to say the least.

Nothing made any sense and I firmly didn’t understand what I was doing. I could get some of the most basic things to work, but nothing more advanced—certainly not enough to do anything interesting. I also made the mistake, understandable at the time, of trying to learn from the ground up. So I started by learning how to make lists and move numbers around, which was dull enough that it made all the frustrations even more frustrating. I think I got as far as changing filenames before everything constantly breaking became intolerable. I gave up, set it aside, and went back to PowerPoint.

But then, at the beginning of this month, Rhett Allain posted this video on Reddit. I’ve always looked up to Rhett’s articles in Wired, and seeing him use Python so effectively in that video was the kick I needed to try it again. The tab with that video remained open for a couple days while I tried and tried again and tried a third time and tried some more to install something that should be far easier than it is, but eventually everything was working as desired. The trick, I learned, is that when you see an error, just keep uninstalling the things that throw the error until there’s nothing left to uninstall. Then try again, rinse, and repeat. (Note: This does not constitute actual advice. Although it did, in a sense, work for me.)

I set about following Rhett’s guide and it, delightfully, worked. After that, I was off to the races. Everything was (mostly) beautiful and nothing (some things) hurt. I added another mass on a spring below his and learned how to make sliders to adjust the initial positions of both masses, then went back and made a bunch of other simulations and toys to expand my horizons as I went.

It’s been going well so far and I’m having a lot of fun, but now I have the problem where I have a lot of good projects on my computer and the only one looking at them is me. I wanted to change that and share what I’ve been working on. To that end, I’ve added an Educational Resources page to this site with links to all the projects that I’ve put onto Trinket. They’re all available to use by educators and anyone else seeking to develop some physical intuition.

I’ll keep updating that page as I make more, and I’m open to new ideas to add to my growing list. I hope people find them useful. They certainly are fun to make.

Recess -> Stationery

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I miss recess. Also Recess. That theme really brings me back.

A recess is more than a great TV show from my childhood. It’s another word for a hidden gap. Recesses surround us, in bookcases and closets and cabinets. But recesses get much smaller than that, too. The proteins in our bodies fold into complicated shapes that no one understands even today, but we know enough to say the recesses in those structures are part of how proteins do their work.

Smaller still, surfaces are pitted and pocked all over the place on atomic and molecular scales. These bumps (and larger ones) are the source of friction, as we saw a couple posts ago. But let’s zoom out from that scale to a paper towel. We find recesses there, too. If you take a maker and make a dot on a paper towel, you’ll see the dot expand even after you take the marker away. This happens as ink flows in and out of recess between the fibers of the paper towel, pulled along those fibers by capillary action: Each molecule gets pulled forward by the fiber a little in front of it and pulls the molecules behind it along, too. (That’s loosely stated, but we can’t do everything all the time.)

Capillary action is why notes written in pen on paper towels start out neat and end up looking like ransom notes. Paper towels are made to be particularly good at pulling liquid along the fibers. That way, the part that’s actually touching the source of the liquid can keep sucking up more instead of saturating, and the paper towel cleans up whatever spilled. Paper, though, is made a little differently. Its fibers don’t shuttle liquid around quite as much and ink generally sits more on top than soaking in. But ink still bleeds a bit, even with the best of papers. If you don’t want closed es and gloomy qs, write in pencil on stationery.

Of course, pencil smudges. But that’s neither here nor there. (If anything, it’s both.)

Blizzard -> Tank

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Growing up, I thought adults who said “nor’easter” were bad at saying “northeaster”. I was wrong.

Just about all nor’easters—a sort of winter tropical storm, for those not from New England—count as blizzards. But a blizzard is more than a bad snowstorm. It’s a winter storm with high winds and enough snow in the air to keep visibility fairly low for at least three hours. Since light bounces off snowflakes, the more snow in the air, the closer something has to be for most its light to get to you without being bounced all over the place first. Whether that snow came from the clouds or it was picked up from the ground by wind doesn’t come into play in defining the storm.

Snow muffles sounds just as it bounces light, but for a different reason. The coordinated vibration of molecules that forms a sound jiggles water molecules in the snow around and becomes random vibrations (heat). (Also, winter storms tend to have funny temperature distributions that refract sound upwards and away from our ears.) During a blizzard, with howling winds and sound-absorbing snow everywhere, you can only hear really loud stuff from afar—loud stuff like thundersnow.

But sounds dissipate with distance even without snow. Some of the coordinated vibration of a sound wave always turns into heat as sound travels through the air. Higher frequencies are especially susceptible: They start with more rapid vibrations at the outset, so it’s easy for those to get out of sync and become random noise. Also, it takes more energy to sustain more rapid vibrations, so the sound runs out of energy sooner. This means treble dissipates too quickly to be heard from a great distance. The farther you are from something, as a result, the lower-pitch it tends to sound. (Side note: This is also why people who live upstairs from you always tend so sound like they’re stomping and grunting rather than squeaking.) (Second side note: This is tangentially related to something I talked about for the Museum of Science [24:17 in that video is the question and then my answer], where you can tell the angle of a lightning bolt from the sound of the thunder.)

What’s true for natural processes is also true for natural processes that humans have a hand in—there’s nothing to be gained in separating us from nature, after all. So if you’re far from an outdoor concert, you’ll hear more bass drums, low voices, and low guitar chords. And if you’re close to a tank when it fires out of the big barrel, you’ll hear a wide spectrum of noises. But if you’re a ways away, you’ll mainly hear a boom. Hopefully you’re far away in the right direction.

Friction -> Cashier

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Last day of doing this daily! After today I’ll settle down to weekly like I planned.

Friction between pieces of sandpaper has an obvious source: Sandpaper is lumpy. But lumps and bumps, whether at centimeter or atomic scales, are the source of any friction between two surfaces that are rubbed together. When bumps of one encounter lumps of another, they catch. (Everything is also made of electric charges that fleetingly attract the charges of other surfaces. On really big scales, this sort of process helps make lightning. But that’s a story for another time.)

Overcoming friction means shoving atoms out of the way, jiggling nearby atoms in the process. So friction turns useful energy into useless energy—what physicists call entropy. Those two sentences say the same thing, by the way. One just focuses on atoms while the other is bigger-picture. But I think it’s easiest to understand friction if you switch zoom level mid-sentence: Friction turns kinetic energy (energy of large-scale movement) into heat (energy of atomic movement). The more heat you get, the less kinetic energy you keep—and kinetic energy is the energy we use to power things like engines.

Energy is constantly changing forms. That’s all it can do, dark energy aside. It can’t appear or disappear. But as we’ve already seen, some energy is useful and some isn’t. The second law of thermodynamics says that over time, we’ll run low on the former while accumulating the latter.

The universe, then, is like a cashier who only gives change in pennies. Sure, you might pay for something with exact change (you might find some process that turns 100% of useful energy into other useful energy), but honestly that’s pretty rare and never really happens if you have a complex bill. The rest of the time, you put in more energy (more money) than you need, and the change you get back is completely useless.

Admittedly, we should probably try to pay in exact change during a coin shortage. I’m sure there’s a metaphor for renewable energy in there somewhere.

Cutlass -> Fuel

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My first thought was to go from fuel through fire to blacksmiths, but I’ve gone down that road already. Let’s flip it.

A cutlass is a sword, and swords have to be sharp. (It’s also a kind of car, which has to be sharp in a different way to cut through the air.) But we’ve been sharpening things far longer than we’ve had swords. Members of our genus have sharpened tools for millions of years. We’ve gotten good at it by this point. We’ve gotten so good at it that the Ancient Greek philosopher Democritus used a knife to reason his way to a fledgeling atomic theory.

Here’s what he said: When you cut into an apple, some of the apple ends up on either side of the knife. But the only way the knife can get between the two parts of the apple is if there was already space between them. So there must be bits of matter with empty space between them. QED—or whatever the Ancient Greek version of QED was. It’s not quite the argument we’d use today, but it’s neat, even when summarized as fleetingly as I just did.

Modern atomic theory came from the dual directions of physics—where atoms explained temperatures and sounds and a bunch else—and chemistry—where atoms explained reactions. Chemical reactions seemed to consume the input elements in certain ratios, and we now know it’s because a certain number of atoms of one element would always react with the same number of atoms of the other: Two oxygens and one carbon became carbon dioxide, say.

Fire, as we know from the other day, is a complex collection of chemical reactions involving oxygen. But fires need two other ingredients. They need heat and, of course, they need fuel.