Researchers know why popcorn kernels burst open, but they’ve long puzzled over the source of the "pop" sound. When popcorn heats up, the moisture inside turns into steam, building up pressure until the hull splits and fluffy white corn bursts out, often as the kernel sails into the air. The pop, slow-motion videos reveal, happens out of sync with the hull's rupture and the corn's launch into the air, eliminating two possible explanations for the noise. That left one remaining cause: The sound comes from the release of water vapor as the kernel opens, the team reports online today in the Journal of the Royal Society Interface. The sudden change in pressure when water vapor is released causes cavities inside the popcorn to vibrate and produce sound, the researchers suggest—much like a champagne bottle's pop when uncorked. The scientists also discovered the mechanism for the kernel's acrobatic hop into the air. Like a gymnast doing a flip, the popcorn "pushes off" with a starchy leg as it expands—visible in the video above—causing it to jump and somersault. In the snack Olympics, the nimble popcorn gets a perfect 10.
(Video credit: Alexandre Ponomarenko and Emmanuel Virot)