Daily Archives: April 13, 2009

Rolling Followup

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Last week I posted Rolling, Rolling, Rolling, with the video about the moment-of-inertia problem with the liquid-filled and ice-filled soda cans. Nick submitted the post to reddit (Thanks!), and I got a spike in traffic about 25x normal, for a day or so. That makes it (by far) my most popular post to date, and also the most popular home-grown post (I had gotten a spike or two from some interesting links I had posted).

One of the questions asked at reddit was what would happen if the ice was fee to move inside the can, so I tried that experiment — and there was no noticeable change. Even though the ice was riding on a layer of water it still spun up, and to the resolution of the video, the lag between the ice can and liquid can is the same. Water has pretty strong adhesion to a surface, and the entire interior surface of the can and exterior surface of the ice are interacting, so this shouldn’t be that surprising. Liquids, on the other hand, can be thought of as a very large number of layers (laminar flow), which gives much weaker coupling.

There are one or two other experiments I could run that require a sealable container, and so aren’t convenient with soda cans. I should be able to acquire some transparent sports bottles that should do the trick. If I can think of any comparisons that give non-intuitive results, I’ll post them.

Spicing it Up

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Green Eggs and Toast

Changing standard storytelling as an exercise in challenging kids. Plus, it’s fun. I’ve done these and similar things with my nieces. The fill-in-the-last-word is something I learned from someone with a background in child development, and the replace-a-word I do just because I love kids’ sense of the absurd (and finding the line where pretending becomes just silly). Changing the story has its dangers, though — it can be upsetting if you aren’t doing it right and the child isn’t in the mood for it.

Uncle’s tip: Always negotiate how many time you’re expected to read the book before you start. They’re minors and contracts aren’t legally binding, but it’s some leverage, at least. You get tired of reading the book long before they tire of hearing it … again.

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Getting a Charge Out of Buckyballs

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“Superionic” Buckyball Crystal

A team of researchers from Italy, Hungary, and the UK reasoned that buckyballs bonded into a crystal structure, like stacked fruit, would generate a material with big spaces in between the spheres. “To create large channels, we need large building blocks,” says team member Mauro Riccò of the University of Parma in Italy. And each buckyball can accommodate multiple negative charges, good for incorporating many positive ions. But which ion to use? Previous experiments found that sodium ions couldn’t move easily between the buckyballs.

The smaller lithium ion is a much better choice, Riccò and his colleagues report after completing a long characterization of their new compound, which consists of four lithium ions per buckyball.