When a balloon pops

Balloons burst with a single tear when the internal pressure is below a certain limit (top). For pressures greater than that, the skin fragments into pieces (bottom).

When a balloon pops, how many pieces does it break into? A study using high-speed video shows that there are two different bursting modes -- a single tear and several tears -- and this study by Sébastien Moulinet of the Ecole Normale Supérieure (ENS) in Paris also tells you why and what distinguishes them. The researchers inflated sheets of rubber into balloon shapes in a reproducible way and popped them. According to their video data, it all depends on the stress in the rubber sheet, determined by the pressure inside the balloon. While in moderately inflated balloons, a single crack can relieve the stress, but above a threshold pressure they break up into multiple fragments. The breakup happens instead by the radial spreading and branching of a series of cracks from the puncture point, creating parallel rips and fragmenting the balloon skin into several pieces

It was sheer curiosity that led to think about this problem, say the scientists. “I started to get interested in this question after seeing an artistic photograph of an exploding balloon,” he says. “I noticed that the cracks seemed to be separated by the same distance” and that they advanced in parallel. These properties can produce a kind of “rib-cage” structure of fragments. The researchers suggest the finding may be applicable to a wide range of fragmentation processes, from the break up of heavy nuclei to the bursting of bomb shell cases. The work has been published in a recent issue of Physical Review Letters .

R. Ramachandran