Faraday + “premelting” / liquid-like surface layer

4:18I want to I want to see what what what you'll come up with. But in any case, that's the central um question that I want to answer today. And in fact, I'm not going to answer it because the research is still ongoing, which is quite incredible. It's such a simple question, right? Like why is ice slippery? It's relevant to stuff like glaciology, like, you know, glaciers moving off continents into the oceans and then raising our sea levels. It's relevant for transportation. You don't want to slip on ice. >> Um, and obviously it's relevant for winter sports. Um, the standard explanations are pretty bad. >> Okay. >> Okay. They seem satisfying from like a high school physics level. Oh, okay.

4:58There's a layer of water and then the water makes it slippery. But when you just go a little bit deeper, it doesn't make any sense. And it's it's actually quite interesting. So let's go to the 200-y old question, right? 200 years ago, there was this guy Michael Faraday. He is the greatest of all time in terms of experimental physicists. You can come at me in the comments again. This guy is the goat. Okay. Um >> he's also actually the founder of scientific communication. It wasn't Carl Sean. Okay. >> People think that Carl Sean was this first guy. No, Michael Faraday used to have Christmas lectures at the Royal Institution where he would demonstrate electricity and magnetism for the common

5:40public and there are these very famous, >> you know, outreach events that happened in the 1800s in London. So, you know, this guy's an OG and I I love everything about him. And one of the many things that he did, he did, you know, electricity and magnet magnetism is what he's really famous for, but he actually did experiments all over the place. And he's the first to observe something called regulation, which is this idea that there's a permanent liquid-like layer of water around every ice block. Okay? And people sort of took that observation and said, "Oh, that's why ice is slippery because there's a little bit of water on top." Right. >> I just want to make a quick note.

6:21>> Mhm. >> That we are not talking about the system that puts a Premier League team in England. >> Is that called regulation? >> It's called relegation. >> Oh, relegation. [laughter] Yeah, I've heard that. I've heard that from my cousins are really into Arsenal and they're like, "Oh, >> they're going to get So, for example, used in a sentence, Tottenham Hotspur is potentially in the relegation zone." >> Oh, are they really? >> Yes. However, >> did they have a terrible season, so they're going to they're going to go down? >> They're potentially going to go down. >> How do you feel about that? You're a Chelsea fan. >> I am ecstatic about it. >> Right. Yeah. Okay. That's what I thought. >> I'm ecstatic about It's happened again. It's happened again. Tottenham Hotspur.

7:03It's happened again. [laughter] >> Okay. >> But we're talking about >> regulation. >> Regulation, which just just to be clear here. >> Yeah. Yeah. That's the liquid layer of water on top of ice. And the this liquid layer can be nanometers thick. >> Can be only like a few molecules to tens or hundreds of molecules. Okay. Right. And and [clears throat] for the longest time, Michael Faraday did some experiments that showed that this is true. And for the longest time it was like oh like those water molecules um are what's causing the slipperiness. When we started getting into some deep thermodynamics the Thompson brothers the most famous of whom is Lord Kelvin he started looking at the statistical mechanics of what happens at this

7:45interface between ice and liquid water. Liquid water is very interesting because um just water in general is very interesting. It's one of these unique compounds because of the geometry of the molecule. um it increases in volume when you freeze it. >> This is very strange. This is why ice floats. Ice is less dense than liquid water. The solid phase of liquid wa of water the solid phase of water is less dense than the liquid phase which is why ice floats. This has everything to do with the geometry of the water molecule. the fact that it's 104° between these two bonds of oxygen hydrogen oxygen hydrogen. Um, and for the longest time

8:27that's been kind of the dominant explanation is because the the volume increases. Suppose now I were to press down on ice, right? If I stand on ice with skates or something like that, I'm pressing down. I'm increasing the pressure. And what physics wants to do at all times is resist change. And so when I press and I compress the volume, it's going to undo the freezing part >> and become liquid. Does that make sense? Like like when water freezes, it expands. I'm pushing in. So I'm going to make it unfreeze. I'm going to make the the water sort of come back as liquid instead of being in the solid form. And

9:08that's the >> I mean, I've heard this explanation even from Fineman. There's a really famous interview with Fineman where um a guy asks him, you know, why how do magnets work? And he goes on this random tangent stream of consciousness about what do you mean why does it work? And the interview is like I don't know. It's a simple question. Why do magnets work? And he's like, well, you know, suppose there were an alien around and I said grandma slipped on the ice. How far deep would I have to go into the explanation to tell him what I mean? And then he talks about, oh well, grandma slipped on the ice because ice is one of these unique compounds that is slippery when you stand on it because of the pressure

9:48and all this stuff. And he even cited this thing, right? >> But let's let's just like try to hone in on this explanation. The explanation is I squish the ice, the ice becomes water. >> Mhm. >> Okay. That works for negative temperatures like -2° C, -3°. >> Okay, >> when you're getting to something like -20° C to -30° C, I can still skate on that ice. But this explanation won't work because I'm so cold, no matter how much I press the physics at that scale, the

10:28statistical mechanics of the this bulk body, it's not going to let the water come out. The idea being when temperatures are colder,