Popcorn has lots of physics behind the little pop. Until recently, popcorn had only been studied for it's chemical properties and never the physics behind why it pops the way it does. It comes from the fact that their is water in the kernel. When it is heated above 100 degrees Celsius, the water turns to steam and expands inside the kernel. It continues to expand until the shell can no longer support the pressure and it eventually pops. As soon as it pops, the starch cools it down and ultimately turns it into the white flake of popcorn.