In 2017, a juggler named Alex Barron broke a record when he tossed 14 balls into the air and caught them each once. The feat is fascinating to watch, and it becomes even more impressive once you understand the physics behind it.

As WIRED explains in a new video, juggling any more than 14 balls at once may be physically impossible. Researchers who study the limits of juggling have found that the success of a performance relies on a number of different components. Speed, a.k.a. the juggler's capacity to move their hands in time to catch each ball as it lands, is a big one, but it's not the most important factor.

What really determines how many balls one person can juggle is their accuracy. An accurate juggler knows how to keep their balls from colliding in midair and make them land within arm's reach. If they can't pull that off, their act falls apart in seconds.

Breaking a juggling world record isn't the same as breaking a record for sprinting or shot put. With each new ball that's added to the routine, jugglers need to toss higher and move their hands faster, which means their throws need to be significantly more accurate than what's needed with just one ball fewer. And skill and hours of practice aren't always enough; according to expert jugglers, the current world records were likely made possible by a decent amount of luck.

For a closer look at the physics of juggling, check out the video below.