The
Mathematics of Trash
Measuring classroom wastes over time helps elementary students grasp
the magnitude of our waste problem on a meaningful level
By Kate Nelson A
CROSS THE INDUSTRIALIZED WORLD, the amount of solid waste sent to landfills each year is hard to fathom. Did you know that the United
States cranks out about 250 million tons (approximately 225 million metric tons) of residential and commercial waste per year?1
In Canada, 30 million tons per year are generated2 Australians generate approximately 35 million tons3
That’s approximately 500 million cubic yards. , while
. While
students understand that these are big numbers, it can be hard for them—and many adults—to really grasp the mag- nitude of these volumes. After all, when was the last time you saw 250 million tons of anything in one place? The following lesson uses mathematics to help students
grasp the waste problem on a more familiar and meaningful level. These activities are appropriate for 3rd through 5th grade students studying graphing and multiplication, but they can easily be adjusted up or down.
Materials: Bathroom scale, graph paper, calculators, classroom trash
Time: 10 minutes/day for five days, plus 45 minutes for calculations and discussion and 30 minutes for a classroom trash audit
Background knowledge for teacher: • Information for the calculations, i.e. number of classes in the school, elementary schools in the district, number of days in the school year
• General understanding of landfills (http://science.how-
stuffworks.com/landfill6.htm is a good place to start)
• General understanding of your school’s and/or commu- nity’s recycling program
Goal: Students will understand that while one person’s gar- bage may seem inconsequential, it adds up to an enormous number when taken as a whole. They will also understand that most of this garbage goes to landfills, and landfills have environmental consequences.
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Procedure: To begin, have the class weigh all the waste in the classroom trashcan at the end of each day for one week. Since it can be tricky to balance a bag directly on the scale, one solution is to have a student weigh her or himself holding the bag, and then again without the bag. Then subtract the latter from the former. Graph the trash weights for each day and find an aver-
age. You will most likely get a number that is just a few pounds or kilograms. Now the multiplication can begin. First, ask the class to multiply their average daily trash weight by the number of classes in the school building. Ask them, “If our class makes “X” pounds/kilograms of trash on average each day, would it be reasonable to assume that other classes at our school make about that much?” This may initi- ate some lively conversation about which grade generates the most waste, but more importantly it will give the students an idea of how much trash their school is generating each day. Next, the class needs to figure out about how much
waste is generated by the entire school (not including lunch- room waste) each school year. (Be sure you have the number of days in the school year at hand.) Multiply the amount of waste that the class previously calculated for all of the school’s classrooms by the number of days in the school year, and now you should have a nice, large number that will likely surprise the students. If you would like to continue, ask the class, “Could we assume that most elementary schools in our school district
GREEN TEACHER 89
Illustrations: Tom Goldsmith
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