Lesson 6 of 14
Objective: Students will grapple with the physics that governs the exchange of energy between two or more objects.
The goal for this lesson is to expand student understanding of the flow of energy. If an object has a limited amount of energy to provide (for example, a heated rock), it has a different impact on a water bath than an electric heater that essentially has unlimited energy to provide. The related physics - in this case, the conservation of energy - can be highlighted more effectively by examining the "limited energy" case.
Having become familiar with how an object responds to a heater with virtually infinite energy, I ask my students to consider the temperature profile of a cool water bath when a hot object is dropped into it (see resource entitled "calorimetry prompt"). In addition, I want to see their sketches of the hot object's temperature profile.
I give them two minutes to work solo and record their thoughts in their notebooks. After that, I ask them to share their thoughts with a neighbor after which we discuss as a class what we think will happen to these temperatures over time. It is helpful to invite students to the board to show their initial ideas - these often reveal important pre-conceptions about the flow of energy or, in the case below, some deep insight. The student whose work is shown below captured the idea that, given sufficient time, both objects will return to room temperature - the application of conservation of energy taken to the next level!
My overall goal here is to get students to consider the movement of thermal energy from one object to another. I look for opportunities to invoke the conservation of energy and push the discussion until it seems clear to all that the temperatures of the two objects will converge at a common final temperature.
I show students an on-line simulator that allows them to explore variations of the thought experiment we have just considered. A link to the home page is here. (The name of the exact simulation is "Calorimetry Lab." And, though one may create a free trial account for 30 days, access to the simulations and teacher-generated support materials is through an annual subscription.) The "simulation screenshot" includes a sample output from the simulation.
I spend just a few minutes demonstrating the controls and the outputs of the simulator. The goal here is to simply familiarize students with the "bell and whistles" so that they can concentrate on the upcoming task at hand. The examples also nicely reinforce the idea that, independent of the materials or initial conditions, the substances will always converge on a common final temperature.
Having shown the simulator, I then prime the class with the Big Question: Can we assemble enough data, and develop enough intuition, about this phenomenon so that we can write a formula that predicts that common final temperature?
I hand out the Calorimetry Lab that guides students through a virtual experiment and culminates with that Big Question. The handout is a hybrid document - a series of recipe-like steps and questions meant to guide student thinking followed by the final, higher-order-thinking question. The simulation site provides many of these handouts that have been developed by teachers over time. In this case, I downloaded the recipe questions because I liked the train of thought it developed, then tacked on the Big Question because I wanted that as the culminating experience.
In terms of assessment, this is an excellent example of "assessment FOR learning." The experience is rich and the challenge is great, so there's little need to summatively assess the work. One may decide to acknowledge student participation or collaboration or some other qualitative indicator of engagement, but it need not be scored as a summative assessment. For many students, knowing that their work will NOT be assessed will lower anxiety about "being right" and foster a greater sense of inquiry in the activity.
Exploration via Simulation
I supply students with a set of laptops that can be used to access the simulation. Students are free to use their own computers if available.
I ask students to work together in teams of 2-3. Teams may self-assemble and students often work with friends. Every student, however, is expected to complete the responses to the virtual experiment handout.
The goals here are to encourage conversations about the topic of calorimetry and to increase each student's intuition and experience with these experiments. Due to the virtual nature of the exercise, many trials can be run in a short period of time. In addition, there are some ways in which the achievement of the final goal - of creating an equation that predicts the final temperature - is scaffolded for students.
During this time, I circulate around to each team to check on progress, to resolve any technical issues, and to encourage careful consideration of the questions. The exploration will take from 25 to 35 minutes with any remaining time going into the final Big Question.
Students may, at the end, be somewhat frustrated with their ability to assemble a rule from the data . . . it is a difficult task. Near the end of this time, I share with students that, while I expect them to share their best thoughts today, we'll take another look at this work in our next class.
In the final minutes of class, I have each team share their best thoughts about the Big Question: How close are they to being able to predict the final common temperature for a calorimetry experiment?
An important goal here is to get students to fully articulate their thoughts and to realize whether or not they've made any underlying assumptions along the way. It's not unusual for a student group to come up with an expression that works in some limited way (same masses for the two materials, for example) or works approximately (often, for example, students will claim success if their prediction can be within 10% of the correct answer . . . an error that is way too large for such a virtual lab!).
A rare event is a group coming up with the exact formulation! This is awesome and I celebrate with them but ask them to remain silent during the final discussion. Their moment comes in the next class when I ask students to carefully consider the role of the conservation of energy in this experiment.
Students are expected to submit their papers for assessment before the end of class.