It may not be an Olympic sport yet, but yo-yo play is serious business. Especially in Cleveland this week, where the world’s most skilled yo-yo players are gathering for The World Yo-Yo Contest. The ...

Even the most basic yo-yo tricks depend on the toy’s ability to keep on spinning. But why does it spin so fast for so long? The magic center of a yo-yo is a bearing—a bunch of tiny metal balls trapped ...