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Grades K–2 · Materials & Matter

How does a hard kernel burst into fluffy popcorn?

A small, hard popcorn kernel can become a large, fluffy shape. The picture shows its inside and its popped form. A kernel contains a little water and a material called starch inside a tough outer shell.

P29 visual explanationA popcorn kernel contains water and starch inside a tough shell. Vapor pressure can split the shell; expansion puffs softened starch. The popped record shows the expanded starch after it becomes firm. No new matter is created.A hard kernel becomes fluffy popcornTough shellWaterStarch insideExpanded starchVapor leavesThe larger form contains many spaces.Lines show invisible water vapor leaving.

In the diagramA hard kernel becomes fluffy popcornTough shellWaterStarch insideExpanded starchVapor leavesThe larger form contains many spaces.Lines show invisible water vapor leaving.

The cutaway shows water and starch inside a tough shell. After the shell splits, expanding vapor puffs the softened starch into a much larger shape.

When a kernel becomes hot, its water makes more water vapor. The vapor pushes outward, and the starch softens. The shell holds this pressure until it splits.

The vapor expands as the pressure falls. Soft starch puffs outward and then becomes firm as it cools. The bigger shape has many spaces inside it. It is not made from new matter, and not every kernel pops.

About this explanation

Starting knowledge: Recognizes popcorn, a hard outer covering, water, and a change in an object’s size.

Sources

  • American Chemical Society — The Secret Science of Popcorn
  • USDA National Agricultural Library — How does popcorn pop?
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