An ancient toy could improve health care in the developing world

“So, I asked the [team] to bring more toys into the lab,” Prakash says. And someone brought in a button spinner.

The simple toy, also known as a buzzer, is part of the whirligig family, and has been around for more than 5,000 years. They’re made by passing strings through the center of small discs—everything from buttons to bones and flattened musket balls. By twirling the ends of the strings, you spin the disc and wind the strings together. If you now pull the strings outwards, they unwind and rapidly spin the disc in the opposite direction.

By filming a basic whirligig, Prakash’s team were astonished to find that it could spin at 10,000 rpm. “We realized that this is a toy that no one had thought about,” he says. “The physics of how it works weren’t understood and its fundamental limits were completely unknown. So we spent six months thinking about the math, all with the goal of asking how fast it could really go.”