An extremely brief introduction to the study of Physics . . . with energy thoughts being emphasized as central to a significant portion of what we'll study this year.
I use this time to provide students with the major conceptual link for the year: energy. It's an effort to introduce a major cross-cutting concept and only a slight exaggeration to say that "if one understands energy and all its ramifications, one can truly understand (virtually) all of Physics!"
I also tell students that in every unit we study, we will link our work, somehow, to energy.
During this time, I describe the task to students - to use immersion heaters to heat water and to record the resulting graph using temperature probes and a data acquisition system. I find that this simple activity provides several benefits. First, the concept of energy is central to the events so it is a natural follow-up to the introductory comments. Second, though it is a simple task, there are some complexities to getting good data and students enjoy uncovering them. Third, it's easy to have multiple trials with obvious variations (more or less water, stirring versus not, etc.) and during the lab work, students will need to consider these and decide how to proceed. Finally, like much of Physics, there are some important links to familiar math concepts (e.g. slope). Indeed the next few lessons will build on these math connections.
But first, I want students to pre-think the activity.
Step 1: I show students the Immersion heater: simple devices that use electrical energy to heat an insulated coil. I then ask students to imagine the heater being placed in the water and to guess about the way the water temperature changes over time. I ask them to sketch, in their notebooks, their imagined temperature versus time graphs. Students then compare their graphs with a neighbor and discuss any differences. Finally, I ask for volunteers to come to the board to share their thoughts, making no effort to recognize "correct" answers. The purpose is to get students to unpack their thinking.
Step 2: I demonstrate our probe system (Vernier Temperature Probes) quickly at the board. I use the temperature probe and the Vernier software to show how the probe responds to my hand. A brief 15-second demo gets the idea across.
Step 3: I share a SAFETY WARNING with students: There is no switch between the hot part of the immersion heater and the wall socket. Once plugged in, the heater becomes hot!! It is imperative that the heater be immersed in the water before being plugged in. I ask that each team assign one person to the sole responsibility of monitoring the use of the heater. In addition, I remind students that immersing the heater in water will keep it from overheating and cracking.
This process provides some investment in the outcome and provides just enough scaffolding for students to be successful without giving away any "answers."
I use the back of my room to distribute beakers, temperature probes, Vernier Labquest devices, and immersion heaters to student groups. Other than safety issues, I try NOT to answer any questions about "how much water to use," etc. as I want the student groups to decide these issues. The variety of approached will enrich later discussions.
I place students, randomly, in groups of 3-4 to collect data. Given my class sizes that typically means 4-6 groups, which is manageable. Larger groups are undesirable as the tendency to become disconnected from the work grows. Students collect materials from me and spread out in the lab section of the room.
My goal, during this time, is to prompt thinking about their procedure, their results, and the assumption that ALL of the energy from the heater is getting into ALL of the water. This is an important assumption and is not accomplished without stirring water - an aspect students won't immediately consider. Best practices result in very linear temperature responses.
The Vernier LabQuest collect real-time data and display the resulting graphs on-screen.
As students create sample graphs (both linear and non-linear), they can save them to a flash drive and copy them onto my desktop for later review. Even the non-linear results are worth considering. I use a class flash drive to be shared and students have access to my computer - this frees me to continue to circulate around the lab stations.
After creating at least one linear graph, I ask students to extend the investigation by varying the amount of water and predicting the resulting graph.
After about 30 minutes, I ask students to join me for a large group discussion.
I pose several key questions for discussion:
- What are best practices for generating good data?
- Why, from a "physics point of view," should you stir the water?
- Did the resulting graphs look like your predictions?
- What did your predictions suggest about the way the water would change temperature?
These are on the board and I allow a minute or two for students to consider them before entering into a large group discussion. This is very informal and students may consult one another as they consider the questions. As they have all participated in the exercise, there is little anxiety about the answers - this is a time for summarizing and reflecting. When ready, I open the discussion and try to get as many students involved as I can. One technique I use is to simply ask students to raise their hand if they've got some confidence in a particular question (for example, the second one above). I count the number of hands I'm seeing out loud . . . and tell students I'm waiting to see at least six responses. This way I can manage the discussion, minimize the domination by a few, and stimulate more participation.
As we discuss these points, I show several of the examples collected from students during the lab work phase. This allows me the opportunity to demonstrate some features of the software, including the "best-fit line" feature. From this we can get a slope . . . and begin the discussion of the meaning of the slope.
My goals during this time are to summarize ideas for good practices, to stimulate thinking about the transfer of energy from the heater to the water, and to reflect back to the speculative graphs created at the beginning of class.
As this is day one of school, students have lots of questions about the course, grading, expectations, etc. While all of this is posted electronically on our class bulletin board, I hand out the Physics Expectations and Grading Policy and take some time to address these questions.
In particular, I point out to students that each assignment will be linked to one (or more) of our school's six Learning Expectations: we want all graduates to be Collaborative Workers, Self-Directed Learners, Responsible Citizens, Effective Communicators, Skilled Information processors, and Complex Thinkers. This allows me, for example, to tease apart one's timeliness with an assignment (Responsible Citizen) from one's depth of response (Complex Thinking).
Before class is over, I want to return to the theme of energy transfer. I ask students to consider a variety of scenarios where some aspect of the lab work has been altered. For each scenario, I want them to record their sketch of their expected temperature versus time graph. I ask them to work solo and to come to the next class ready to articulate their thoughts. Ideally, students do this before leaving class, though they have until the beginning of next class to finish the task. (See sketching thermo graphs resource.)
My goal is to stimulate the connection between the physical properties of the system (amount of water, heater "strength," etc.) and the resulting mathematical properties of the graph. I want students to develop the habit of mathematically modeling a physical system.