Unit 3: Considering the Influence of Light and Thermal Phenomena on Local Weather
Many US states have adopted the Next Generation Science Standards (NGSS, Lead States, 2013). In addition to science and engineering practices and crosscutting concepts, this document recommends disciplinary core ideas that student should learn at various grade levels.
A. Learning about the US Next Generation Science Standards: Disciplinary Core Ideas
Question 3.13 What NGSS science and engineering practices, crosscutting concepts and disciplinary core ideas have you used in developing an explanation for the occurrence of hot sand, cool water, clouds, and sea breezes late in the afternoon after a sunny day at the beach?
The Next Generation Science Standards describes disciplinary core ideas in terms of learning progressions (NGSS, Lead States, 2013, Appendix E) (See: https://www.nextgenscience.org/resources/ngss-appendices.) These indicate what students should learn about a topic in Kindergarten-2nd grade, 3rd-5th grade, 6th-8th grade and 9th-12th grade.
Disciplinary core ideas in physical science, for example, include:
PS3.B Conservation of energy and energy transfer:
- During Kindergarten-2nd grade, students should learn that sunlight warms Earth’s surface.
- During 3rd-5th grade, students should learn that energy can be converted from one form to another form.
- During 6th-8th grade, students should learn that the relationship between the temperature and the total energy of a system depends on the types, states, and amounts of matter.
- During 9th-12th grade, students should learn that the total energy within a system is conserved.
- How are these disciplinary core ideas relevant to the development of an explanation for sea breezes?
- Provide an example of how the explanation of sea breezes incorporates one or more of the eight NGSS science and engineering practices: asking questions and defining problems; developing and using models; planning and carrying out investigations; analyzing and interpreting data; using mathematics and computational thinking; constructing explanations and designing solutions; engaging in argument from evidence; and obtaining, evaluating, and communicating information.
- Provide an example of how the explanation of sea breezes incorporates one or more of the seven NGSS crosscutting concepts: patterns; cause and effect; scale, proportion, and quantity; systems and system models; energy and matter: flows, cycles, and conservation; structure and function; and stability and change.
The disciplinary core ideas, science and engineering practices, and crosscutting concepts are called dimensions of science learning and teaching. It is important to consider all three dimensions when designing learning experiences in science contexts.
B. Reflecting upon this development of a complex explanation
Explaining sea breezes is complicated. As the conversation with Ava above illustrates, however, even four-year-old children know that “hot air rises” and can support that claim with evidence “in our room during the summer it was always way hotter on my top bunk than it was on Ruby’s bottom bunk. And it was way hotter at the top of the house than in the downstairs…” This four-year-old already has understood the essence of the nature of science, being able to make an argument based on evidence. Young children are capable of scientific reasoning in contexts with which they are familiar and have had relevant experiences upon which to draw in making sense of what they are learning.
What happens when energy radiated from the Sun shines on sand and water at a beach in the same way for the same time? A more complex version of Ava’s scientific reasoning occurs in making an argument about what happens when different materials absorb incoming energy. One way to explore this question is to create a model of the situation in the laboratory. What happens when energy radiated from a lamp shines on equal masses of sand and water in the same way for the same time?
The graphs in Fig. 3.17 and 3.19, for example, demonstrate a major difference in that the temperature versus time line for the sand was clearly steeper than the line for the water. This replicates the effects seen at the beach, that equal input of energy results in very difference changes in temperature for sand and water. Using specific heat information from outside sources indicated that the specific heat of sand was about 0.2 calories of energy to change the temperature of one gram by one degree C whereas the specific heat of water was by 1.0 calories of energy to change the temperature of one gram by one degree C.. This difference in the property of specific heat, in how much energy is needed to change the temperature of one gram of a material by one degree Celsius, is the key to explaining why sand at the beach is hot and the water cool even though the sun has been shining on both in the same way for the same time.
Differences in other properties, such as thermal conductivity and reflectivity, also contribute to causing this effect. The temperature near the bottom of the cup of sand was lower than the temperature near the surface, whereas the temperature of the cup of water was the same throughout. This indicates that the sand had a low thermal conductivity. This means that the incoming energy absorbed by the sand stayed near the surface, warming the surface sand whereas the incoming energy absorbed by the water on the surface flowed throughout the cup of water. Using reflectivity data from outside sources also demonstrated that reflectivity effects were minor compared to the big difference in effect due to the property of specific heat.
Tracing the flow of energy in a system also is useful in understanding what is happening. As shown in Fig. 3.14, convection occurs when a circular current forms as warm fluid rises and cold fluid sinks. Similarly, as energy flows from the warm sand to the dry air above it by conduction, the less dense warm air rises; as energy flows from the warm air into the cooler upper atmosphere, the cooling air becomes more dense, and sinks back down toward the surface, setting up a convection current. Meanwhile some of the liquid water absorbs enough energy from the sun to evaporate into the cool air above the water’s surface. As the warm air rises above the hot sand, the cool moist air above the surface of the water blows toward shore, forming a sea breeze. When the moist air warms, rises, and cools in the upper atmosphere, the moisture condenses back into liquid water droplets and forms clouds.
Developing this complex explanation of local weather that students have experienced at the beach seems to be motivating. Several have identified this session as a highlight of the course. The pleasure students seem to experience in this accomplishment may help them to appreciate the hard work of figuring something out as well as understanding the emotional satisfaction that scientists derive from their studies.
One goal of this course has been to build confidence in using the tools of science, particularly graphs and diagrams. Creating a graph of data and telling the ‘story’ that the graph displays can be a powerful skill to have, both professionally and personally. Also powerful is the ability to create and use diagrams that visually explain whatever needs explaining. In addition, the process of articulating what was done, found, and understood in this complex context can help students gain confidence as science writers, able to set forth their own ideas and reasoning in clear and coherent ways.
C. Making connections to NGSS understandings about the nature of science
This unit provides a good example of the NGSS science and engineering practice of constructing explanationsas well as the crosscutting concept of cause and effect in focusing upon the difference in the property of specific heat for sand and water. The very low specific heat of sand compared to that of water causes large differences in increases in temperature when light from the Sun shines on sand and water in the same way for the same time. This is an example of aspects that students in grades 3-5 should learn to do, to identify the evidence that supports particular points in an explanation. They also should understand that the transfer of energy can be tracked as energy flows through a designed or natural system while they are learning disciplinary core ideas about the conservation of energy and energy transfer.
Unit 3 also has provided additional examples of the nature of science such as that science knowledge assumes an order and consistency in natural systems (NGSS Appendix H https://www.nextgenscience.org/resources/ngss-appendices . This unit assumes, for example, that what happens with small amounts of sand and water warmed by a lamp in the laboratory is consistent with what happens with large amounts of sand and water at a beach. Also assumed is that similar mechanisms cause the apparent paradox that the sand is very hot but the water is cool even though the Sun is shining on both in the same way. The students explored possible causes for these different effects by considering the role of differences in three properties of sand and water: their reflectivities, thermal conductivities, and specific heats. They observed differences in how much the temperatures changes on the surface when energy flowed from a lamp placed equal distances from cups of sand and water.
The process of explaining why the sand is hot but the water cool as well as why sea breezes and cloudy skies often appear in the afternoon after a sunny day at the beach was a culmination of the earlier explorations of the nature of light and thermal phenomena. Students may gain from this exploration some understandings about how scientific knowledge grows and connects in multiple ways across many contexts. The process of engaging friends and family members in learning about sea breezes at the beach also may help convey some of these understandings about the nature of science to others.