That, in itself, would be interesting enough. But the real surprise is that the chain doesn’t just run over the edge. It rises up in a curve, like a water fountain, as it falls.

“I came across it by accident,” he said in an interview. “I was looking for a physical model of a polymer,” a long molecule. He thought a chain of beads would work, and in the process of investigating that possibility he saw a demonstration of plastic beads self-siphoning from a container, tumbling over the edge.

Photo

Beads leap out of a jar in an arc before falling to the floor, pushed up by some force. CreditSteve Mould

“I thought, ‘I want to reproduce this, but I think metal might look better.’ ” He tried it, and to his surprise the chain rose like a charmed snake. The video, posted about a year ago, went viral, and John Biggins, a Cambridge physicist, saw it.

He had been talking with another physicist at Cambridge, Mark Warner, about a project Dr. Warner was working on, an online course to improve physics education in high school. Dr. Biggins brought the chain fountain video to Dr. Warner’s attention and they agreed it was an ideal problem to present to students because it involved Newtonian physics, not some extreme variant of string theory or quantum mechanics.

Then they realized that they didn’t actually understand it.

The fountain, said Dr. Biggins, which he had never seen before the video, was “surprisingly complicated.” The chain was moving faster than gravity would account for, and they realized that something had to be pushing the chain up from the container in which it was held.

A key to understanding the phenomenon, Dr. Biggins said, is that mathematically, a chain can be thought of as a series of connected rods.

When you pick up one end of a rod, he said, two things happen. One end goes up, and the other end goes down, or tries to. But if the downward force is stopped by the pile of chain beneath it, there is a kind of kickback, and the rod, or link, is pushed upward. That is what makes the chain rise.

Dr. Biggins said they explored this possibility partly because of earlier findings by a Cornell researcher, Andy Ruina, on a different, but related, problem in falling-chain physics.

Finding a new physics problem in an Internet video was, Dr. Biggins said, something of a treat. For a scientist it’s “reassuring” that new problems like this can pop up, he said.

He and Dr. Warner published their paper on Jan. 15 in the Proceedings of the Royal Society A. And the chain fountain is now, as Dr. Warner hoped, part of a physics course for high school students.

As for Mr. Mould, he is touring at the moment as part of a science comedy show called “Festival of the Spoken Nerd,” in which he talks about the chain fountain.

One of the most enjoyable performances, he said, even for an Oxford graduate, was in Cambridge last month, because Dr. Biggins and Dr. Warner, who had talked to him about their research, attended the show.

“They were in the audience,” he said, “with the whole physics department.”

A version of this article appears in print on March 4, 2014, on page D4 of the New York edition with the headline.

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