Hello and welcome to No EffortNovember, a series of videos for the month of November in which it is becoming increasingly obvious the title is a misnomer. Today’s video is about lava lamps! Yes, those things that hang out in the set unceremoniously. Just don’t their globular thing. Speaking of misnomers, unless the lamp has broken the lava is inside the glass so shouldn’t they be magma lamps?
These are important questions. Lava lamps have been a personal object of fascination for many years. They are objectively pointless objects, producing little to no usable light, and take literal hours to become operational, especially for larger ones, but once they’re going they’re downright transfixing and hypnotic. And the way they work is stupidly simple but at the same time - surprisingly complicated. And that’s what we’re gonna be talking about today. First, the anatomy of a lava lamp. Inside the base is an incandescent light bulb, often some kind of appliance bulb, and then when you put the globe on the base you end up with what amounts to a weird bottle on top of a light bulb. And that light bulb has to be incandescent because these things work thanks to the heat they generate, so it’s a good thing they use appliance bulbs since they’re unlikely to be phased out.
Can’t exactly put an LED bulb in an oven, can you?
But as is the case for many things in life, it’s what’s inside that counts. Clearly there are two substances inside this bottle: a clear one, and a not-clear one. Clearly they don’t want to mix, and it’s also clear that the not-clear one is some sort of wax, clearly. When the lamp is cold, it forms a big ‘oil clump at the bottom and some gentle inverting and shaking reveals that, clearly, this is a solid. That much is clear. Indeed, anyone who’s ever owned a lava lamp and watched it warm up knows just how clear it is that we’re dealing with a wax.
Except of course those who are both too impatient and too careless to read the labels plastered on the things that say to be patient and then leave product reviews claiming it doesn’t work - those people are lots of fun.
Anyway, a fun, frequent phenomenon found in flava flamps when they warm up is the Spiky Tower of Wax. You’ll often find that the clump of wax at the bottom sort of pushes itself upward as the wax nearest to the bulb melts and expands, You don’t always get the Spiky Tower of Wax, sometimes you just get the Bloaty Glob of Indigestion, or the Fantastic Flippy Flip. No matter how the wax behaves in the beginning, it takes until the entire globe has warmed to the point that all the wax has melted (and can stay melted), and then you get variously colored jigglies. What a callback! Now here’s where our friend physics makes for some magnificent magma magic.
The wax, much like most substances out there, expands when it melts. Water does the opposite because it’s cheeky, but anyway once the wax melts its density is almost exactly that of the mysterious clear liquid. That means it’s not exactly gonna float, nor is it gonna sink. It’ll just be suspended somewhat. But luckily for us, its density - and thus its buoyancy in the mysterious clear liquid - varies a tiny bit with its temperature.
And also luckily for us, because the heat source is at the very bottom, we get a temperature gradient across the globe’s length with the hottest parts being at the bottom, and the coolest parts being at the top (farthest from the lamp). So, we end up with this cyclic behavior where the wax starts at the bottom, gets heated by the lamp, becomes ever-so-slightly buoyant in the mysterious clear liquid thanks to thermal expansion, and then it floats to the top. Once there, it cools a bit since it’s far from the light bulb, which causes it to contract ever-so-slightly, and thus it is no longer buoyant but in fact sink yant, and then it sinks back to the bottom. If you’ve watched a lava lamp for any period of time you’ll know that these globs of wax don’t really want to combine with one another.
But there needs to be something to force them back together otherwise at some point you’ll just end up with a bunch of teeny tiny beads floating around as they continue to break apart. So, at the bottom of the globe is a coil of wire which serves to break the surface tension of these globs and force them into one big glob again. Thus the lamp can operate continuously.
This also keeps the wax in contact with the hottest part of the glass at the bottom, making it heat faster and keeping things moving. Now, you might be wondering what this heretofore mysterious clear liquid is. Or for that matter, the wax. Ordinary candles are made of our ‘old friend paraffin wax, which melts at fairly low temperatures and so seems like would be a good candidate.
But paraffin wax is much less dense than water and would never sink in it, so if it is paraffin wax, the mysterious clear liquid would have to be something else. Now there are clear liquids out there in which paraffin would sink, but many of them are flammable and thus pose a problem. A large quantity of, for example, acetone in a glass bottle above a light bulb would probably not get UL approval. Plus, many of these potentially OK liquids would mix with the paraffin and we can’t have that
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