Why Does Popcorn Pop?

Jennifer Martin-Kochis & Jennifer Washuta

For Mrs. Cutlerís 3rd Grade class



This mini-unit is an inquiry based science project that explores the question, "Why does popcorn pop?"



This mini-unit will develop the studentsí skills of prediction, observation and communication of scientific findings.  These are essential skills for scientific investigation.


Prior Knowledge

Students have eaten popcorn.  Some may know that popcorn starts as a kernel and, when heated, explodes to form the popcorn that they eat. The students have learned that there are different types of corn. They have been developing the scientific skill of observation.


Standards  -

5.1, A.1. - Raise questions about the world around them and be willing to seek answers through making careful observations and experimentation (lessons 1-3)

5.1, A.2. - Keep records that describe observations, carefully distinguish actual observations from ideas and speculations, and are understandable weeks and months later. (lesson 1-2)

5.6, A.3. - Recognize that water, as an example of matter, can exist as a solid, liquid or gas and can be transformed from one state to another by heating or cooling. (lesson 2)



Give each student some popcorn (both popped and unpopped). Ask them to write/draw their observations of the popcorn in their journals. Then ask the question, "Why does popcorn pop?"





  1. At the end of this lesson, students will be able to describe the inside of a popcorn kernel. 

ASSESSMENT:          -Student will label a diagram of a popcorn kernel.

  1. At the end of this lesson students will be able to formulate a hypothesis.

ASSESSMENT:          -Given a diagram of a popcorn kernel, students will create a hypothesis about why popcorn pops, using information provided during the


  1. Distribute popcorn to each student.
  2. Instruct students to observe the popcorn closely and write their observations in their journals.
  3. Define observation, hypothesis and conclusion. 
  4. Have students write the definitions in their journals.
  5. Distribute diagrams of the inside of a popcorn kernel.
  6. Using whole group instruction, label the parts of the popcorn kernel on the diagram.
  7. Include the following information in your discussion of the popcorn kernel:

-high starch content in the endosperm

-endosperm contains moisture

-strong, hard hull

  1. Instruct students to place diagrams of popcorn kernels in their journals.
  2. Instruct students to use what they learned about a popcorn kernel to make a hypothesis about why popcorn pops and write their hypothesis in their journals on the page labeled Why does popcorn pop?



            -Why does popcorn pop?

            -Why do you think so?



            Students Journals (1 per student)

            Popcorn kernels, unpopped

            Popped popcorn

            Diagrams of inside of unpopped popcorn kernel (1 per student)






  1. At the end of this lesson students will be able to explain that water changes from a liquid to a gas when heated. They will be able to expand on their hypothesis of why popcorn pops, using this knowledge.

ASSESSMENT:          -Students will write in their journals the observations they made of heated water.


  1. Review that there is water inside the popcorn kernel.
  2. Using a hot plate heat a pot of water. (Alternatively, remove the lid from an insulated cup containing hot water)
  3. Instruct students to write observations about what they see in their journals.
  4. Define liquid, gas, and steam.
  5. Explain that when liquids are heated they turn to gas and that water in its gaseous state is called steam.
  6. Explain that steam takes up a lot more space than liquid water.
  7. Ask students what will happen to the water (which they learned in the previous lesson is contained within the popcorn) when the popcorn is heated.
  8. Explain that I will blow up a balloon to illustrate what will happen as the water inside the popcorn turns to steam.
  9. Instruct students record their observations of what happens in their journals.
  10. Instruct students to describe the research they performed today.
  11. Instruct students to use their observations from today's research to evaluate their hypotheses, and (if necessary) make any adjustments for future testing.



            -What did you observe?

            -Why is this happening?

-Yesterday we learned that the endosperm, inside the popcorn kernel contains water. What will happen to this water when you heat the popcorn?

-Based upon your observations and our discussion today, do you need to change your hypothesis about why popcorn pops?



            Students' journals


            Cup full of water to be heated on hot plate

            (Alternative - insulated cup containing hot water)







  1. At the end of this lesson students will be able to explain that popcorn pops due to a combination of several characteristics of popcorn kernels.

ASSESSMENTS:        -Students will draw conclusions based on the observations they have made over the course of the investigation.

-Students will complete a worksheet about the sequence of steps involved in popping popcorn.



  1. Pop a batch of cracked popcorn kernels.
  2. Instruct students to record their observations in their journals.
  3. Pop a batch of regular popcorn kernels.
  4. Instruct students to record their observations in their journals.
  5. Review our findings through the course of the investigation and formulate a conclusion about why popcorn pops.
  6. Ask if the conclusions support the hypotheses the students had made (original and adjusted).
  7. Instruct students to write their conclusions in their journals.
  8. Complete the Popcorn Sequence worksheet.
  9. Read the story "The Popcorn Book" by Tomie DePaola.




-Why didnít the cracked corn pop?

-Based on your observations today, do you need to change your hypothesis about why popcorn pops?

-What conclusions can you draw based on the observations you have made during this investigation?



Read The Popcorn Book by Tomie DePaola while students snack on popcorn.


Individualization - The journals are the students' personal records. There will be no rules for keeping them other than that someone else who wanted to review their research must be able to understand what their hypothesis is, what they observed, and what their conclusions are. They may use words, pictures and/or charts.