Science's association with popcorn goes beyond the development of the perfect corn variety for popping. Researchers have demonstrated the laws of physics at work as popcorn pops.
In a study published in the Journal of the Royal Society Interface, Emmanuel Virot and Alexandre Ponomarenko showed how different fields in physics (biomechanics, thermodynamics and acoustics) were evident in the popular snack, deviating from the usual research that tackled practical issues, such as the best shape for and optimum level of moisture in a kernel.
The researchers wanted to get to the bottom of the physical origins of some of the most distinctive characteristics of popcorn, such as what makes a kernel jump and the sound it makes as it pops.
"To the best of our knowledge, the physical origin of these observations remains elusive in the literature. Here we discuss the possible physical origins with elementary tools of thermodynamics and fracture mechanics," they explained.
Inspired by their colleagues' work at École Polytechnique's hydrodynamics laboratory, Virot and Ponomarenko used a high-speed camera capable of capturing 2,900 images per second. To observe in detail how popcorn pops, the researchers aimed the high-speed camera at a hot plate, dialing up the temperature to 662 degrees Fahrenheit and placing a few kernels of popcorn on top.
Based on hundreds of trials, Virot and Ponomarenko found that popcorn flies a few millimeters to a few centimeters into the air, kicked up by a "leg" of starch emerging from a popped hull. From the time the hull breaks and the starch leg is released, it only takes no more than one-fifteenth of a second. Furthermore, steam played no part in making popcorn jump.
For the sound popcorn makes, the researchers came up with three possible causes: pressurized water vapor being released; rebound from the pop; and the fracturing of the hull. To find out what causes popcorn to make that popping sound, a high-end microphone was used, synchronized alongside the high-speed camera.
The microphone did not capture any sound the moment the popcorn opened, so hull fracturing was ruled out. The kernel further cracked open about 100 milliseconds later, but it was still after six milliseconds that a popping sound was recorded. This meant that the popping sound popcorn makes was due to pressurized water vapor being released, much like the pop a cork makes when a champagne bottle is opened.
Virot is currently working on his doctoral degree in École Polytechnique. Ponomarenko received his in 2012 and is now in the middle of a postdoctoral fellowship with a government agency in France.
