This past October, 245 daredevils wearing harnesses attached to ropes jumped off a 30 meter (98 foot)-tall bridge near São Paulo, Brazil, in an attempt to set a world record. Thanks to physics, the stunt was a success—and no one got hurt.

The daredevils needed to ensure they wouldn’t decelerate, or slow down, all at once when they reached the end of their ropes. That’s why they chose to use climbing ropes with plenty of elasticity. This ability to stretch helped to slow the jumpers’ descent gradually. “If the rope is too stiff, the deceleration will be very fast, which could be damaging,” says Jim LaBelle, a physicist at Dartmouth College in New Hampshire. Rapid deceleration is what causes the harmful whiplash effect in a car accident, he says.

After the rope stretched to its limit, the pendulum effect took over. The jumpers began moving in a side-to-side motion typical of a pendulum. The friction from air resistance then slowed the jumpers until they came to a complete stop.