My physics kids told me about cereal coming together on its own in the bowl, and I thought they had to be nuts.
Today they showed me Trix in water in a beaker. Darned if they don’t draw together and even kind of snap together. The pieces even snap to the side once they get close enough. They keep arguing that it’s gravity, but I know that gravity is very weak, and that it can’t be that. On the other hand, these pieces are actually snapping together in a visible way. Who’s got the straight dope on this?
My WAG is that the trix pieces are making small “dents” in the surface of the liquid, and the other pieces will float down these “dents”, eventually sticking together. It’s a little like the concept of gravity in relativity.
Hmmm… in chemistry there is the concept that “like molecules attract”; that is, things that are of similar polarities will tend to be drawn together, and will avoid things whose polarities are very different. This is why water and oil don’t mix. The water is very polar, and oil is very non-polar, so there isn’t really anything to cause them to want to be together at all. Using an intermediate solvent, such as an alcohol, could cause a better mixing, because the alcohol has a polar end (the -OH that defines it as an alcohol) and a non-polar end (the carbon-hydrogen chain that determines whether it’s ethanol, methanol, propanol etc) and so water will be attracted to one end, the oil to the other, and you can get some sort of solvation happening.
Twix, and most cereal, are made primarily of carbohydrates, which aren’t especially polar. They also don’t dissolve well in water. So the “like” molecules that make up the cereal will be repelled by the water/milk, which will cause them to drift around until the cereal pieces meet each other, and they will be content to stick together.
That is, admittedly, a WAG. A slightly educated WAG, but a WAG nonetheless
Yes, non-polar sticks to non-polar instead of polar (actually I’m a chemistry teacher stuck into some other subjects also at this school). But we would have to say that the polarity is so strong that it attracts the pieces from a distance of about 1/2 an inch. Also complicating things is that they are attracted to the side of the beaker, when we all know that the water level rises in the meniscus at the side.
I’m sure ethanol and water are different densities, but since they’re both polar, they’re attracted to each other to an extent that keeps them from separating. Pour mineral oil into water, though, and you get a separation because the water is too attracted to itself to bother parting and letting in the oil molecules.
This is what I learned back in the day, too. Imagine placing two balls on opposite edges of a trampoline. They both press down on the trampoline, making little crater-shaped impressions. If those crater-shaped impressions wander close to each other, they they’ll both roll to the bottom of the newly-shared crater.
In a bowl of milk, take special notice of the edges of the bowl. Milk is somewhat adhesive – that is, it sticks to the bowl a bit. The milk “crawls” ever so slightly up the edges of the bowl, meaning the surface is not perfectly flat. A pair of Trix could easily “roll” down the side hills and end up sharing a crater. Alternatively, if the Trix actually touched the side where the surface tension broke, a thin film of milk “crawling” up the side of the bowl and up the side of the cereal, making a very weak sort of glue function.
Now keep in mind I’m trying to remember either a lesson from 9th grade physical science or an episode of Mr. Wizard I saw as a kid. Take this with a grain of salt, and this admittedly unscientific corroboration.
Carbohydrates are extremely polar on most scales. They are also readily dissolved in water. Starch can be difficult to dissolve, but that is more of a size issue.
I have also heard that gravity and “dents” in the surface are what cause this phenomenon. I suspect that surface tension and the meniscus shape may have something to do with it.
