At some point during the first trimester, one of my 8th grade classes and I were having a discussion about chemical reactions and we veered in the direction of fuels, such as gasoline. We talked about the reaction between gasoline and oxygen in engines, but it quickly became apparent that they had never seen the inside of a combustion engine. It occurred to me that no middle school student should be allowed to advance to high school without having seen the “guts” of a motor! So as a unit ending activity we embarked on a dissection, of a sort.

I put a request out to the Mater Christi School community to see if parents had any old, broken, or unused lawnmowers that they might be willing to donate for this lesson. Many mowers were generously donated and my students took them apart piece by piece until light shone upon the pistons and cylinders at the heart of the machines.

This deconstruction experiment was a great way for the students to unify the concepts of Matter (Chemistry) and Energy (Physics). We saw how the combustion reaction releases chemical energy that we can use by converting it to mechanical energy to cut our grass or drive a car. We discussed efficiency as well as how much of the energy held in the gasoline is lost as heat.

The students loved this experiment and for many, they had their first interactions with socket sets, mallets, hack saws, and other implements of destruction. We kept the engines so that other classes can benefit from their work, and all of the other scrap metal was sold and the proceeds were donated to the 8th grade trip fund. If you have an old lawnmower that you would like to donate for next fall’s crop of “Decontruction Engineers”, please let me know.

Mr. Mark Pendergrass
Middle School Science Teacher
mpendergrass@mcschool.org

Photo Credit: Ambient Photography
www.ambientphotography.com