Beacon Lesson Plan Library

What Happened to the Popcorn?

Lois Walsh
Bay District Schools


This is a laboratory demonstration assessing the students' understanding of the law of conservation of matter by weighing the mass of popcorn before and after being popped.


Selects and uses direct (measured) or indirect (not measured) methods of measurement as appropriate.

The student understands that there is conservation of mass and energy when matter is transformed.


-Bag of Microwave Popcorn
-Metric balance


1. Gather materials and set them up.
2. Read over procedure.
3. Review safety procedure and first aid.
4. Prepare students and monitor their progress during demonstration.


The popped bag of popcorn is very hot. Steam burns. Caution students to be very careful.

The Law of Conservation of matter and energy says matter cannot be created or destroyed, it’s transferred. This demonstration is used as an assessment of the students’ understanding of this concept. It could be modified to introduce or practice the concept.
The popped popcorn will weigh less because the water evaporates.

Demonstration Directions:
1- Gather the materials.
2- Present the problem to the class:
What will happen to the mass of the popcorn when it's popped?
3- Have the students start their lab report/assessment with:
- The problem as the title
- Hypothesis
- Leave space for the experimental procedure summary
- Set up a data section with before and after mass measurements and observations.
4- Weigh the bag of unpopped popcorn and record the measurement (remove the plastic wrap).
5- Pop the popcorn in the microwave. (see the bag’s directions for popping times)
6- Challenge students to record any observations of changes or actions as the popcorn is removed from the microwave. Caution: it is hot. Observations should include volume, temperature and steam. Open the bag partially to draw attention to the steam. Comment on the heat of the steam (but not the steam). Note: since most popcorn bags will only sit flat on their side to be weighed, do not open the bag all the way or it may spill. Allow sufficient time for the steam to vent as students record observations.
7- Weigh the bag of popped popcorn and record the measurement.
8- Challenge the students to analyze* and conclude what occurred.
*Analysis can include how much of a change and percentage of gain or loss in mass. (% = Difference in mass divided by Initial mass x 100)
9- Collect reports and assess.
Note- The aroma and taste of popcorn often inspires young scientists and eating the popcorm is a safe and effective method of disposal when handled properly.


Students will complete a lab report with:
-Title --Data measurements & observations
-Data Analysis ( mathematical work shown)
-Experimental procedure summary
If done correctly, the popcorn will weigh less because the water evaporated. Students should be able to relate the law of conservation of matter to the mass not disappearing but transferring to the air.


-See Beacon Learning Center Lesson Plan: ‘GUM: More, Less, or the Same?’ for another law of conservation of matter lab activity. Lesson available on this site.
Return to the Beacon Lesson Plan Library.