Reflection: Rigor Measuring the British Thermal Unit - Section 5: Expand


One of the difficulties in understanding how energy is measured is that energies are measured in different units. Students have a hard time understanding the unit of Btu. Comparing a Btu to a calorie helps to link the concepts -- but providing evidence of understanding is difficult.

I have had difficulty with the prompt responses for the prompt, "The energy in a calorie is like __________________.  "The energy is a Btu is like _______________________." 

The prompt did not generate the understanding I was hoping to tap. I wanted to assess understanding of the degree of difference between the two energy measurements. The energy in a calorie is like eating popcorn. The energy in a Btu is like eating three hamburgers and four pizzas."

The students answered the prompt by comparing the size of the calorie to the size of the Btu. Unfortunately, the next question, "There are two measurements of energy because………", student responses included size again. "One is for big energy. One for smaller." I won't use those prompts again. 

My intention for asking the question was to get responses about natural gas being burned vs. food energy being used. Most students did not link the large numbers of Btu with energy outputs. It was as if the size of the numbers distracted the students. I tried several different prompts and had the same result with some students.The last data table, comparing the energy output of kilowatt, gallons, short ton, and Btu was surprisingly understood. Before asking them to rank the energy outputs, I explained the data table in detail. My strategy of linking the data table with previous lessons paid off. Using the Bunsen burner as an example, we compared what we learned about kilowatts from the Kill-O-Watt Lesson, the Btu's in the nut lab, and previous experience with gallons of gas. We converted the coal short tons to grams and I used my hunk of coal to help students understand how much coal is .00006 short tons.

My additional time pulling together prior learning really helped. Most students ranked coal as using the least amount of raw material for the energy. There was a surprising class discussion that I did not anticipate.  At one point I asked, "What makes this so hard?" Students explained it was hard to compare energies for two reasons: unit differences and the size of the numbers. I loved what they said because I knew that to understand, students had to reason abstractly (understanding units) and quantitatively (comparing numbers).

(Common Core Math Practice #2)


  Reasoning Abstractly and Quantitatively
  Rigor: Reasoning Abstractly and Quantitatively
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Measuring the British Thermal Unit

Unit 4: Measuring Energy
Lesson 3 of 4

Objective: SWBAT identify a British Thermal Unit as a measurement of energy. This lesson integrates science practices with mathematical reasoning.

Big Idea: Students can be better stewards of their energy uses by understanding how energy is measured. This lesson helps students understand British Thermal Units.

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