Scuba Diving -> Electrical Outlet

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I’m surprised “electrical outlet” was a “Hard” Pictionary result. That seems like a pretty easy thing to draw. Regardless, let’s get diving.

Scuba diving involves taking a tank of oxygen underwater, which is necessary because humans, tragically, are only fish in the most pedantic of senses. We need to breathe oxygenated air, and the oxygen we breathe comes from plants: We’d suffocate without them, while they’d be fine without us. They make oxygen using plentiful carbon dioxide and water. But where does that oxygen come from—the stuff in the carbon dioxide and water molecules? We’ve got a ways to go, so let’s make this answer quick: Mostly molten rocks, and also some dead stuff.

But that doesn’t satisfy me yet. Where do the actual oxygen atoms come from that have been kicking around our planet for billions of years? They don’t come from chemistry or geology. They come from physics. Stars bigger than the Sun make oxygen all the time out of carbon and hydrogen (and another hydrogen), although admittedly most of it then turns into nitrogen. Dying stars of all stripes make more lasting oxygen by smashing together carbon with helium. When really big stars die, they explode in a supernova, blasting oxygen and other elements out into the cosmos. (Sun-sized stars typically hold onto the heavier elements they make, although evidence is mounting that they often end up growing big after they die and exploding anyway.) We breathe—and are made from—the ashes of ancient stellar explosions.

Stars themselves are made of plasma, which is either a fourth state of matter or a super-hot gas, depending on whom you ask. If you ask someone who’s focused on molecular motion, plasmas and gases are the same thing: Substances whose molecules zing around so quickly that they don’t clump together. But if you ask someone focused on conductivity, they’ll say plasmas and gases are quite different. In a plasma, the molecules move so fast that electrons are knocked off of them, creating a sea of charge through which electricity can flow quite easily. Plasmas are conductors, while most gases are much too diffuse to conduct electricity.

Back down on Earth, of course, we don’t have to seek out a plasma to find something conductive. We have metals that we form into wires and plugs. Plug something in and electricity—electrons—flow down the conductive wire from the electrical outlet.

Fiancé -> Shelter

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When I proposed to my now-wife, I didn’t have a ring. Finding the ring size of someone who doesn’t wear many rings seemed hard, getting and keeping one in secret seemed harder, and I didn’t see the point when really I just wanted to marry her. She said yes anyway. (I think she liked me.)

That made me her fiancé, but, in one of English’s few remaining vestiges of nouns with grammatical gender, it made her my fiancée. Most fiancés have fiancées with diamond rings, both because of some pretty impressive marketing and because diamonds are well suited for finger adornment. When cut right, diamond can exhibit total internal reflection, where (loosely speaking in a way that would make some people mad) an incoming ray of light bounces around multiple times inside the diamond before coming out. This property makes diamonds seem to glint and shine from all angles, which in turn makes them glimmer when they’re on something that moves around a lot—like a finger.

Some diamonds are synthetic and some form from asteroid impacts, but let’s ignore them so that I can say: Diamonds are forged deep within the planet, when buried carbon is squeezed by immense pressures from something like colliding (or newly forming!) tectonic plates. The incredible pressure shoves carbon atoms into their most rigid possible arrangement—so tightly and perfectly packed that it’s nearly impossible to move an atom out of the way. This makes diamonds incredibly hard to scratch. But it also makes them relatively rare, at least compared to normal rocks. So as cool as it would be to live in a diamond house, it’s just not happening.

Instead, we make homes out of much more common stuff. We use wood where there’s a lot of wood. We use stones, sand, and water (and other stuff) to make concrete. We use mud and clay to make bricks. We use sand again to make windows. All of them make for a pretty sturdy shelter. And, honestly, I’d rather have privacy than a diamond house, anyway.

Hot Tub -> Shampoo

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Okay, so there’s the obvious route: Hot tubs are like bathtubs, where you’d usually use shampoo. But there’s not much science along that path. Let’s see if we can forge another one.

Hot tubs are so relaxing because heat loosens our muscles, which is a big-picture way of saying that blood vessels dilate when they’re warm—letting our bodies transport bad stuff out of muscles and good stuff into them. (That itself is a big-picture way of avoiding biology.) There’s probably some biochemistry that goes into dilating warm vessels (there definitely is), but there’s also some pretty straightforward physics. Something’s temperature is a measure of the internal kinetic energy of its atoms and molecules: The hotter the object, the more its molecules wiggle and jiggle. Cold things tend to be rigid because their molecules don’t have the energy they’d need to adjust their positions much. Warmer things loosen up, and they also tend to expand: their molecules can spread out now that they have the energy to push their surroundings out of the way. The same must be true for the walls of blood vessels.

This is fundamentally why we clean with hot water, too. It gives grimy molecules the energy they need to break free from whatever they’re affixed to. An awful lot of kinds of molecules dissolve in water, so anything loosened by the heat tends to be carried away by the water. Washing with soap and hot water is even better—at least as far as dirt is concerned. Soap molecules either bond with or otherwise break into bits of oil or dirt, and it’s easier of molecules to react and rearrange when they have a lot of energy.

Ridding any surface of oils and dirt is the central job of any soap. Soaps get specialized because we might not care very much if a soap is designed to mount an all-out attack on a plate (ceramic can handle it), but we’d probably care more about a soap that does such a good job cleaning our hair that it destroys the hair in the process. That’s why we use gentler stuff on our hair: Shampoo might not be quite as good at breaking bonds as dish soap, but the trade-off is worth it for something made to be gentle. We also want stuff in our hair that washes away easily, and shampoo is designed to be just that.

There. That was a more interesting route, huh?

Chimney -> Spoon

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Chimneys only work because hot air rises, which it does for reasons that I’m sure I’ll explain in more detail someday. But today is not that day. For now, we can just content ourselves with that statement and move on: Hot air rises. That’s not where my interest here lies, anyway. My interest lies at the bottom of the chimney. The fire in a fireplace can get pretty hot, anywhere from 500 to 1,100 or so degrees Fahrenheit. (That’s 260-600 Celsius, if you’re into that sort of thing.)

There’s a lot of complicated chemistry in a fire, but this is a physics blog. We can imagine the whole thing as reactions that combine oxygen from the air with carbon—making carbon dioxide—and hydrogen—making water—in the wood. Those reactions give off energy (loosely speaking), and that energy both sustains the fire and heats the surroundings. It can seem unbelievable at first that fires give off water, but you can prove it to yourself the same way Michael Faraday did: Put a piece of glass above a burning candle and, among the soot, you’ll see condensation. The soot is evidence of the chemistry I’m avoiding; the condensation is evidence of water.

Anyway, fireplace fires can be hot, but they’re nowhere near hot enough to melt most metals. Silverware used to be silver, sensibly enough, and silver melts at 1,700 degrees. Today’s utensils are often made of metals like aluminum instead of silver, but the melting point (and the broader point) is effectively the same. You’re not getting there in your home fireplace, no matter what kind of fancy system you’re running. Getting an oven that hot requires reinforcements. You often need to burn the remnants of ancient wood and other plant matter—what we’d more conventionally call coal. (Or propane. Or something else that burns that hot.) Once your oven is that hot, you’re able to melt all sorts of metals, pour them into molds, and form them into whatever shape you want.

The other option, of course, is to make your spoon out of something that melts at a low temperature, like gallium. Gallium spoons are a pretty popular gag among chemists, although it’s not an element you want sitting around at the bottom of your tea.

Bike -> Drums

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When you learn to ride a bike, adults tell you it’s easier to stay upright the faster you’re moving. I suppose some kids take this as license to rocket downhill, but I was never one of those kids. I always heard it as one of those lies adults tell you. I’ve never liked going particularly fast, and I always balanced just fine.

What I didn’t know at the time is that bicycles can balance even without a rider—and generally the faster they go, the better they balance. Now, there are arguments about exactly why bikes balance, with factors including the conservation of angular momentum, which makes it hard to twist a rotating object (like the wheels); a sort of drag on the front wheel that turns it in the direction the bike tilts, keeping it under the frame; and the distribution of mass in the frame, which forces it to fall toward the front wheel rather than sideways, even when the frame tilts. As interesting as that argument is, it won’t get us to drums. For that, we need the bike to fall.

You realize how heavy bikes are when one falls on your leg, but you also realize how loud they can be. They sure can clang, especially if they land on pavement. That clang comes from vibrations in the metal frame that start as soon as they’re hit by something hard like a rock. The more rapidly the metal vibrates, the higher-pitch the resulting sound. But you can’t easily change how quickly something vibrates by hitting it a little differently, at least not if you abstract away from the real world (as physicists are wont to do). Everything around us has its own resonance frequency—its own natural rate of vibration where it’s easiest for the atoms and molecules in the structure to exchange energy back and forth. Something’s resonance frequency depends on a bunch of stuff, and the actual sound you hear when something’s hit depends on even more stuff. But let’s keep abstracting away from that mess to find a good rule of thumb: If you have a bunch of tubes of the same kind of metal, longer tubes will make lower pitches when struck. The bulk of the frame will have a lower-pitch clang than the adjustable tube that the seat sits atop.

This is also true for the air inside the tube. If you blow over the top of a tube, longer ones will make lower notes than shorter ones. Pipe organs make music this way, as do flame-fueled Rijke tubes.

The source of all these sounds is microscopic vibrations, whether in the air inside the tube or the tube itself. All sounds are produced this way, even without a tube in sight. Sounds come from vibrations. And the rule of thumb holds true more widely, too: More material generally makes lower pitches because it’s hard to get a lot of stuff moving (as long as you keep everything else the same). The less energy it takes to get something moving in the first place, the more of that energy can go into vibrations.

This is why we can hear the difference between kinds of drums—say, between snare and bass. The snare drum is tiny and makes a high-pitched sound; the bass drum is much larger and makes a correspondingly lower-pitch sound. Admittedly, the drum heads might sometimes be made of different material, and also a snare often has stuff at the bottom to shake the sound up a bit, but that’s really neither here nor there.

And that’s the thread of continuity between bicycles and drums.

As a side note, I’m going to kick off this blog by doing one post a day for the first week, then I’ll settle down into the weekly schedule.

What Is This?

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Science is beautifully interwoven. The light we use to understand the Big Bang is the same kind of light we use to heat up leftovers. The telescopes we use to see distant galaxies focus light the same way an inflated balloon can focus sound. The low pitch of rumbling thunder sounds the way it does for the same reason upstairs neighbors tend to sound like grumbling brutes rather than dainty mice. And so on. The more deeply we investigate the inner workings of our material universe, the more interconnected its processes and its physics seem to be.

In this blog, I want to explore some of those interconnections. My plan is simple: Every week, I’m going to go to this Pictionary word generator, set “Number of Things” to 3, “Category” to either Medium or Hard, depending on how I’m feeling that week, and hit “Generate Pictionary Words.” I’ll pick two of the words that pop up and write a little arc of physical connections from one to the other. I’ll post a screenshot of the result from the website, too, just to keep myself honest.

The goal, I suppose, is to be somewhere between an educational read and a good, regular writing exercise. Hopefully it turns out to be both. I can’t promise perfect rigor; I’ll do my best to source claims and double-check my writing, but there’s always a chance I read something wrong in my haste or just write something wrong. I certainly won’t always use semicolons correctly. Why expect anything more from my physics? If someone reads the blog and points out an error, I’ll correct it in the next post—and if that error breaks the chain from one topic to the next, I’ll find another way to connect them. I’ll also thank them for reading, because that’s about the nicest thing a person can do when another humans writes something.

On that note, whether you’ve read this far or skimmed to the end of this introductory post, thank you for reading.