As we were eating our bed time snack this evening, I started asking my kids about why popcorn pops. My son said, " I don't know." He was interested though, so I explained that the kernels had water inside of them. I asked whether the energy was going in or coming out of the popcorn. (It's going in.) I explained that the energy going in changed the water from a liquid to a gas. We examined a popped kernel to see where the seed coat ended up.
Then my son had a better idea.