Practical applications of intermolecular forces

So we just got back from a stay at Balatonlelle, a small town on the south side of Lake Balaton. For those who haven't heard of it, Lake Balaton is locally known as the "inland sea", although it is a freshwater lake, because it's quite large. It's about 77 km long, with an average width of about 10 km. It's also amazingly shallow -- average depth is apparently around 10 feet, if you can believe Wikipedia. Our own experience supports this (but of course 3 days playing on a beach isn't exactly empirical) -- we could go at least a couple hundred yards and still touch the bottom. I guess the shallow shoreline is really common on the south side of the lake.

The first day we arrived fairly late, and I'd been up late the night before, so we didn't do much. That night and into the morning it rained and was fairly cold. It was incredible! I hadn't felt cool in a long time. I actually wanted my sweatshirt on!

But the day after that we got to play at the beach. It had been quite a long time since I'd played at the beach. The first day I don't really remember what we built. I wasn't really very into it. I was still having a hard time remembering how to play on a beach. Does that sound pathetic? Well, it kind of is. But I also think it's really common for adults. We don't get much practice with this playing after we become adults. Even adults who are regularly involved in athletics don't necessarily do unstructured play. Sometimes even when we're parents this happens -- rather than playing with our kids we talk to other adults, or do things on our phones, or read a book, or whatever. No judging here - sometimes it's what you gotta do to stay sane. Anyway, the water was warm, and the kids were having fun. I was feeling paranoid about what to do with my purse, which meant I was having less fun, and carrying my purse everywhere. Even with a shoulder strap, that can cramp one's style. (Purses and things like that are another bane on the life of an adult. But I think I may already have mentioned that in my previous post!)

Anyway, I think the most notable thing we did the first day was rent kayaks for an hour. I was a little skeptical, because Ronan is four, and I wasn't sure he could sit in a boat for that long. To my surprise, Ronan was really into it! We paddled around, looked at birds, and picked up floating plant debris. That's probably when I started to get into it.

So on the second day I was much more ready to engage with the sand. It also helped that Tristan started working with another kid who was already working with a pretty impressive sand construction, and then Ronan and I started working nearby. Eventually the two constructions merged. We made a lake, and then the lake was allowed to overflow and threaten the pyramid (like you do.) But Tristan and his friend were clever, so the pyramid stayed up. We didn't mind.

We arranged to meet this cool kid the next day, too, but we got there a bit earlier than they did, so we started building volcanos. Now it's been a while since I played on a sandy beach, but I don't remember ever being able to build up something made of sand and then have the water stay in it. What I remember is that you dig a lake (see above), and then you keep dumping water in it, and the water stays in the lake for about 2 seconds and then drains out -- so you never really accumulate any significant amount of water, unless you've arranged to have your lake's bottom be below the water table. That was not our experience this time.

I'm not sure I really why I thought it was going to work when I started building a volcano, but that didn't stop me. It sounded like a fun idea in my head, so I just started building it, and it was fun. And then Tristan built a town below the volcano so that we could try to demolish it with the "lava" flow. (So were we doing construction or destruction?) I built the sides up and up and up, and then we filled it with water. It was probably 4 or 5 gallons of water that we put into this volcano. Incredibly, the water stayed in it. Well, we didn't wait for hours, but long enough to fill it, then take some pictures, and then Ronan was stomping the side of it and letting the water flow out. And then we did it again. And again. And again. We had some blow-outs where the sand was too wet. I got better at repairing the hole from the flow, and started to feel like a sand engineer. The insides of the volcano became smoother and more even. I was pretty impressed.

Eventually we built 3 volcanos, and had them all wreaking destruction on the poor town. Check out all that water staying in those volcanos! It was pretty incredible. By the end of the day we had built and filled 5 volcanos, but we were pretty tired by that point -- we'd been at the beach for about 8 hours by then, so we only had them destroy things one time, and we had a blow-out at the last minute, so I don't have photos. But still -- I kind of can't believe I could get that much water to stay in what was effectively piles of sand.

So why did it work? Here's where intermolecular forces come in. This is a slight attraction that some particles have for each other. It's kind of like when you rub pins on a magnet and they sort of stick to each other. For a while. Until the bottom ones start to fall off, or you blow on it a little bit. It turns out that a lot of things (like water and sand) are a little like really wimpy magnets. (Except it's not a magnetic force -- it's an electrical one. But we don't really have a good mental picture for what that would be like, so I'm comparing it to magnets. OK?) The particles are slightly attracted to each other, so they stick to each other a little bit. Not very much, but a little. And if you mess around a bunch, then they stop sticking and fall apart. So this is why you get clumps of sand, and this is why mud sticks to your shoes, and it's also why it takes a lot of energy to boil water.

In this case, I think it mostly had to do with the particle sizes of the sand. The sand at Balatonlelle included some extremely fine particles -- it was kind of dusty. This meant that the water was pretty silty and cloudy on the first day because of the storm the previous day - lots of these tiny particles were still suspended in the water, and hadn't settled out yet. Most of the beaches I've played on don't have that super fine dustiness to the sand. The super fine particles allowed for more interactions between the sand particles and the water (and the sand particles and the water, etc. etc.) -- which meant that the sand held together better, even when I filled its inside with water. I just made sure that there was enough sand piled together that it didn't become saturated with water right away. With the extra fine particles around, that made the water-sand "glue" even more effective than it otherwise would have been. It was a pretty awesome experience. Next time you go play on the beach you can check out what the sand there is like and let me know!