Why does popcorn pop?
For grown-ups: the science
Popcorn pops when hot steam inside a kernel breaks its hard coat and puffs up the starch.
A popcorn kernel contains a small amount of water inside a tough outer hull and a starchy interior. When heated, the water becomes steam, pressure rises, the hull ruptures, and the gelatinized starch rapidly expands and cools into foam-like popcorn.
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Transcript
A bowl fills with fluffy white popcorn. How can a tiny hard kernel turn into that?
Each popcorn kernel has a little water trapped inside its hard coat. Heat makes the water turn into steam.
Steam takes up more room and pushes hard against the coat. At last, the coat cracks open with a pop!
The soft starch inside puffs out as it cools. That puff becomes the fluffy popcorn we eat.
So popcorn pops because hot steam breaks open the kernel and puffs up its starch.