Popcorn  is a variety of corn kernel (seed) which expands and puffs up when heated. A popcorn kernel's strong hull (seed coat) contains the seed's hard, starchy endosperm with 14–20% moisture.

When popcorn is heated to more than 170°C, the pressure inside the kernel gets very high, preventing the water from turning to steam. Pressure from the moisture being heated continues to build until the hull ruptures, allowing the water in the kernel to expand to steam. The kernel to forcefully expand, from 20 to 50 times its original size, puffing up the starches in the endospern to the popcorn shapes we know so well. Pop-corn indeed!

This activity was developed and tested with preschool and kindergarten educators as part of Science World's Big Science For Little Hands program.

Objectives

• Observe the shape, structure, and texture of corn kernels before and after popping.

• Predict the outcome of an experiment.

• Discuss possible changes to, and different outcomes of an experiment.

Materials

• Per Class:
raw popcorn kernels (one or more brands/varieties)
hot-air popcorn popper
paper
glue
pencil or crayons

Key Questions

• Are all the un-popped corn kernels identical? How are they alike?
• How have the kernels changed after being put in the popcorn popper?
• Do you have mushroom of butterfly type popped corn kernels? (See photo in Resource)
• What is happening inside the machine?
• Can you find the kernel hull on the popped pieces of popcorn?
• Where did all the white stuff come from?
• Why might some of the kernels not pop? How might you change these numbers in a second experiment?

What To Do

1. Examine the kernels. Observe their size, shape, texture and colour.
2. Choose a number of kernels to experiment with (e.g. 10, 25). Count out that number of kernels from one type of popcorn.
3. Predict (guess) how many of the kernels heated will pop (e.g. 8 out of 10, or more simply: all, some, none).
4. Pop your corn: put your kernels inside the popcorn popper and plug it in. Make sure there is a bowl under the spout of the popper to catch the kernels. Wait until the kernels are popping less than once every 5-10 seconds, then unplug the machine. CAUTION! HOT!
5. Remove any remaining kernels from the machine. Observe your popped and unpopped corn. Count the number of popped and unpopped kernels.
6. Glue 10 unpopped and 10 popped kernels to a piece of paper to see how much space they each take up.

Extensions

• Draw what you think the sequence of popcorn popping looks like. Watcha slow motion video of popcorn popping.
• Try again with a different brand/variety of popcorn, but with the same number of kernels.
• Try the same brand/variety of popcorn but with a different number of kernels. Is the popped vs un-popped proportion the same this time?

Other Resources

Science World | What makes popcorn pop?

National Geographic Kids | How Popcorn Works

Discover Magazine | The Physics of Popcorn

Survivors

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Egg BB

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Comet Crisp

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

T-Rex and Baby

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Buddy the T-Rex

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Geodessy

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Science Buddies

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.

Western Dinosaur

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.