When a balloon bursts, it doesn't just simply burst. New high-speed camera footage shows that they either snap cleanly open or become covered in many cracks, depending on the stresses within the skin.
A team of researchers from Paris Diderot University have been analysing the exact ways in which balloons burst, inspired by footage of weather balloons bursting at altitude. They actually used clamped latex sheets of varying thickness and tensions, which they inflated until they touched a sharp blade to pop them.
The team found that the way the balloons burst depends on the stress — that is, the tension divided by the thickness — within the material of their skin. At low stress, a single crack forms, spreading out from where the puncture occurs. At high stress, multiple crack propagate out from the same point. You can see the difference clearly in these animations.
Speaking to New Scientist, the team explains that the difference is likely due to the speed at which the crack propagates:
"If you have cracks that go above the sound velocity, it means that the material in front of the crack does not know it is arriving, so it cannot reconfigure its stress and mechanical properties. It cannot arrange itself so that a single crack continues."
It's thought that the finding could help material scientists to design new materials, which fracture more predictably.