But it’s not easy to maintain this balance. That’s because “the center of mass is not a fixed point in your body,” explains Selinger. “You’re constantly moving your center of mass as you move your arms and legs or lean forward, back, or sideways.” With every step, slackliners must lean to one side or the other or straighten or bend their knees to compensate for shifting mass. Otherwise, they’ll fall off the line.
Balancing on a slackline is even trickier than on a tightrope. “It can bounce and stretch and swing and do all of those things at once,” says Iverson. If a slackliner’s movement shakes the line, it can generate a mechanical wave that travels to the anchor and bounces back. “Then you have to deal with it again,” she says. During Iverson’s classes, the wiggling line generated plenty of laughs. And so did miscommunications, since Iverson isn’t fluent in Arabic (the language spoken by the refugees). But before long, some of the kids managed to send the line—slackliner lingo for walking across without falling off.