Unit 2: Exploring the Nature of Thermal Phenomena
What does doing science and engineering involve? Unit 1 introduced common practices such as collecting, analyzing and interpreting data as well as engaging in argument from such evidence. Doing science and engineering also involves ways of thinking that bridge across different science domains. What concepts, for example, do biologists, physicists, and chemical engineers all use in their studies?
A. Learning about the US Next Generation Science Standards: Crosscutting Concepts
Many US states have adopted the Next Generation Science Standards (NGSS Lead States, 2013) for guiding science instruction in their schools. In addition to the science and engineering practices introduced in Unit 1, these standards articulate a group of concepts that are common across many science disciplines. Both the science and engineering practices and these crosscutting concepts are intended to help students learn about and participate in the nature of science.
Question 2.16 What relevant crosscutting concepts have you used in exploring light and thermal phenomena?
- Go to https://www.nextgenscience.org/get-to-know
- Click on Appendix G, scroll down the first page to the list of seven crosscutting concepts that scientists and engineers use across many different contexts:
- Patterns. Observed patterns of forms and events guide organization and classification, and they prompt questions about relationships and the factors that influence them.
- Cause and effect: Mechanism and explanation. Events have causes, sometimes simple, sometimes multifaceted. A major activity of science is investigating and explaining causal relationships and the mechanisms by which they are mediated. Such mechanisms can then be tested across given contexts and used to predict and explain events in new contexts.
- Scale, proportion, and quantity. In considering phenomena, it is critical to recognize what is relevant at different measures of size, time, and energy and to recognize how changes in scale, proportion, or quantity affect a system’s structure or performance.
- Systems and system models. Defining the system under study—specifying its boundaries and making explicit a model of that system—provides tools for understanding and testing ideas that are applicable throughout science and engineering.
- Energy and matter: Flows, cycles, and conservation. Tracking fluxes of energy and matter into, out of, and within systems helps one understand the systems’ possibilities and limitations.
- Structure and function. The way in which an object or living thing is shaped and its substructure determine many of its properties and functions.
- Stability and change. For natural and built systems alike, conditions of stability and determinants of rates of change or evolution of a system are critical elements of study
- Scan the discussion of these crosscutting concepts to see what they are and read about any that you find particularly interesting.
- Put a check in Table II.4 to indicate if you have used a crosscutting concept while exploring light and thermal phenomena in this course.
- For each context, choose one or more crosscutting concepts and describe an example of what you did and learned.
|TABLE II.4 Crosscutting concepts (NGSS Lead States, 2013)|
Explaining pinhole phenomena and estimating the size of an object
Exploring reflection, refraction, dispersion and explaining rainbows
Distinguishing between heat and temperature
Exploring transfer of energy when mixing hot and cold water
|2. Cause and Effect|
|3. Scale, proportion, and quantity|
|4. Systems and system models|
|5. Energy and matter: Flows, cycles, and conservation|
|6. Structure and function|
|7. Stability and Change|
B. Reflecting upon this exploration of thermal phenomena
This unit began by considering what students already knew about thermal phenomena. Children and adults have many experiences in which high temperatures describe hot days and low temperatures describe cold days. They also have many experiences touching objects of many kinds in which some feel colder than others. These prior experiences often lead students to rank paper or Styrofoam, wood, aluminum and steel in order from higher to lower temperatures because these materials feel so different to touch. Most students are surprised to find that items made of these materials all are at the same temperature when measured by a thermometer, rather than by their hands, if the materials have been in the same room for a long time.
Understanding often emerges when someone mentions the idea of room temperature, that objects that have been in the same room for a long time are at the same temperature. A helpful nudge usually occurs when someone comments that maybe the materials differ in what happens when one touches them, that metal differs from paper or Styrofoam in some way.
Eventually someone articulates the idea that energy is flowing from one’s hand into the metals, that metal is a conductor, and one’s hand is losing energy quickly so one’s hand feels cold. Paper and Styrofoam, however, are insulators; very little energy is flowing from one’s hand into the paper or Styrofoam, so one’s hand stays warm. The materials feel different because of their differences in the property of thermal conductivity, in how well energy flows into and throughout the material, but their temperatures are the same if left for a long time in the same room.
This process is an example of what scientists and engineers do when they observe something that seems puzzling. They try to figure out what might be happening in order to explain that puzzle; they ponder how to reconcile different ideas that seem applicable but do not agree. This process of refining one’s ideas often involves separating and clarifying the differences between some closely related concepts that seem initially to be the same such as heat and temperature.
After developing relevant central ideas, this unit also modeled the next step, of figuring out how to represent mathematically the relationships one has been exploring with both experimental and theoretical approaches. A series of experiments led to the inference of an inverse relationship between the amounts of hot and cold water and their changes in temperature when mixed. Many students express surprise at this inverse relationship as their prior experiences with mathematical ratios typically have been with direct relationships, such as the equal ratios of heights and distances involved in pinhole phenomena. A theoretical approach based on the Law of Conservation of Energy, however, confirms this inverse relationship between the masses of hot and cold water and their respective changes in temperature when mixed together. A refinement involves recognizing that the property of specific heat also affects how much energy is absorbed or released when the temperature of a material changes. Development of an algebraic equation representing these relationships makes possible numerical predictions and estimates of quantities of interest.
Students may experience some of the frustration that scientists and engineers often face as they struggle to perceive the patterns in their data, particularly when our simple equipment does not yield precise relationships but only trends when the data are compared in various ways. Students also may experience, however, the pleasures that scientists and engineers experience when finally recognizing and confirming both the conceptual and mathematical models developed.
C. Making connections to NGSS understandings about the nature of science
The Next Generation Science Standards recommends that students engage in three dimensions of learning science by using science and engineering practices and cross cutting concepts while learning disciplinary core ideas. In this unit, for example, students used the science and engineering practice of analyzing and interpreting data when they tracked and interpreted initial and final temperatures while mixing various amounts of hot and cold water. They became aware of the importance of the crosscutting concepts of systems and system models while attempting to minimize energy flowing into the cups and air by pouring the cold water into the hot water rather than the hot water into the cold. During these explorations of thermal phenomena, students learned disciplinary core ideas about conservation of energy and energy transfer.
This unit also has provided additional examples of understandings about the nature of science as articulated in Appendix H of the Next Generation Science Standards https://www.nextgenscience.org/resources/ngss-appendices . The learning progression for the NGSS understanding that science is a way of knowing, for example, includes that middle school students should learn that science is both a body of knowledge and the processes and practices used to add to that body of knowledge. In this unit, for example, students observed that materials left for a long time in the same room have the same temperature even though the materials may feel warmer or colder when touched. From this, the students gained new knowledge about the role of an object’s property, its thermal conductivity, in the rate at which such energy transfers occur. By mixing various amounts of hot and cold water, the students developed mathematical ways of tracking the flow of energy in a relatively simple system. This unit thus initiated explorations of such energy transfer processes. This focus continues in considering more complex energy transfer phenomena during local weather in Unit 3 and during global climate change in Unit 4.