While the popcorn starts popping, show students slow motion videos of popcorn kernel popping:
https://www.youtube.com/watch?v=NCSr18vtjeo
https://www.youtube.com/watch?v=CXDstfD9eJ0
Talk about what is happening in the kernels:
Each kernel has some water in it. (Corn that is used for popcorn has just the right amount of water: 13.5%.) As the hot oil heats up the kernal, the water inside it evaporates to form a gas (water vapour). The shell is strong and watertight so the gas cannot escape.
As the heat increases further, the water vapour molecules move around more and more vigorously, exerting more and more pressure on the inside of the shell. Eventually the pressure inside the kernel is great enough to burst the shell. (This happens at about 180 centigrade, when the pressure inside is 135psi.)
As the shell bursts the pressure suddenly drops again. This causes the water vapour to expand which makes the starch and proteins inside the kernel expand into an airy foam.
Students can inspect the kernels as they eat them, and see that the shell turns inside out from the force of the explosion.
If students have done some acting out the sates of matter already, they can do skits in small groups on what is happening inside the popcorn to make it pop - each student can be a water molecule, or the kernel shell, or a narrator. Gather to view each others' skits.
(Students can prepare their skits as the popcorn pops if it takes a while.)
Make popcorn with a microwave and paper bag; https://www.allrecipes.com/recipe/87305/microwave-popcorn/
Note that cooking too long will burn some of the already popped kernels, so go under time if anything.
Corn kernel molecules and popping explanation link: https://www.acs.org/content/dam/acsorg/education/whatischemistry/advent….
More popcorn info at: https://www.popcorn.org/All-About-Popcorn/What-Makes-Popcorn-Pop
Scientific paper on popcorn popping: https://royalsocietypublishing.org/doi/10.1098/rsif.2014.1247#:~:text=W….
For a lesson on heat:
Popcorn can be made as part of a lesson on heat. Students brainstorm whether the popcorn is being popped as a result of conduction, convection, radiation or all of them.
For a lesson on seeds:
Compare popcorn kernels with the kernels on a corn cob.
