5-E Lesson Template
Convection
This is an inquiry about convection, how it is understood scientifically, how it applies to real world processes, and how students may best learn about it. It uses convection tube exercises from the Catastrophic Events handbook and seeks to elicit metacognition on how the teaching and learning process works from a teacher’s perspective as well as a student’s. It begins with an engagement exercise that goes over all three heat transfer processes: convection, conduction, and radiation.
Convection is most explicitly emphasized in middle school physical science and earth science standards, and also appears, or in some cases is assumed to be known already, in high school physical and earth and space science standards.
Understanding the heat transfer processes from the sun to the earth and within the earth system is crucial to a scientific understanding of climate change and the “greenhouse effect.” An increasing emphasis among science educators on teaching climate change is making it that much more important to understand heat transfer as part of science literacy.
Convection, along with conduction and radiation, is one of the three common ways that heat gets transferred from a hotter mass to a colder mass. Convection occurs when a fluid is heated from below and becomes less dense as a result of its higher temperature. Because it has become less dense than the surrounding fluid, buoyancy forces the mass of heated fluid rise. Heat is thereby transferred upward, in the rising mass of heated fluid itself.
A complete convection cell occurs if the heated fluid rises, releases heat above, becomes cooler and thus denser, and sink backs down due to the force of gravity acting on its greater density. Once it sinks to the bottom it becomes heated again, and the convection cycle continues. If time allows and equipment and supplies are available, we will run a demonstration of a convection cell.
As noted below, though there are few studies of student preconceptions and learning outcomes with regard to convection, it is well known that students at all levels tend to not understand how heat relates to the atomic and molecular nature of matter, tend to not understand that heat is a form of energy that can transform to and from other forms of energy, and tend to not understand the difference between heat and temperature. Therefore, besides the repeated mention of convection and heat transfer in many parts of the science standards, another reason for teaching convection and heat transfer is to work on student conceptions of heat and temperature. The goal is to nurture scientific insight on the part of students into how the atomic nature of matter relates to heat transfer processes
This exercise takes perhaps 90 minutes.
Standards
A more complete annotated listing of the standards to which the study of convection applies is given in the references at the end of the document.
National Science Education Standards (originally published 1996; referenced here to 13th printing, 2008). Chapter 6 (Content Standards), grades 5-8, Content Standard B (Physical Science), Transfer of Energy, p. 154-155. For students in grades 5-8, “The intent at this level is for students to improve their understanding of energy transfer by experiencing many kinds of energy transfer.” Grades 5-8, Content Standard D (Earth and Space Science), Structure of the Earth System, 159-161. For example, knowing about the “hot, convecting mantle.” Grades9-12, Content Standard B (Physical Science), Interactions of Energy and Matter, p. 180, “Examples are the transfer of energy from hotter to cooler objects by conduction, convection or radiation.” Grades 9-12. Content Standard D (Earth and Space Science), Energy in the Earth System, 159-161, refers to convection in the atmosphere, oceans, and mantle.
Revised Washington State Science Standards (2008), EALR 4-5 PS3C, p. 44 (transfer of heat energy), EALR 6-8 PS3B, p. 48, (conduction, radiation, convection as heat transfer mechanisms); EALR 6-8 ES2B, p. 60, (sun warms earth unevenly; uneven heating of earth’s surface drives wind and ocean circulation); EALR 6-8 ES2F, p. 60, (convection in the mantle causes plate motion, earthquakes, and volcanoes); EALR 9-11 PS3A p. 74, (energy is conserved even if transferred); EALR 9-11 ES2A, p. 76 (sun warms earth unevenly; uneven heating of earth’s surface causes weather and climate patterns).
Components
Outcomes
Knowledge. Name the three mechanisms of heat transfer. Describe how each works. Diagram how each heat transfer mechanism works in the case of a flame, such as a burning candle. Explain how a cold base and a hot base affect the temperature of the air above. Draw how convection can be made to occur with two convection tubes joined together and the option of having a cold or hot base in either tube. Describe and diagram examples of convection in the atmosphere, in a storm, and in the earth’s mantle. Explain how volcanoes and earthquakes may both be due to convection in the earth.
Skills. Given a potentially dangerous heat source such as a flame, is able to avoid being burned by convection, conduction, or radiation. Using two convection tubes, can safely set up and demonstrate an example of convection.
The Catastrophic Events guidebook has “Getting Started” questions for formative assessments and questions for “Reflecting…” on the results at the end of each experiment, by way of summative assessments. For our purposes here, a set of assessment questions is given below under Evaluate. One could also consider a written pre-quiz to provide a basis for a direct measure of learning progress.
Materials and Equipment
See the lists of materials and equipment in Catastrophic Events for Inquiries 4.1, 4.2 and 5.1. Each inquiry involves two convection tubes and other equipment and supplies.
Prior Knowledge
For teachers: Can explain what heat is and what temperature is, and why heat always transfers from the hotter object to the cooler object and not the other way around. Able to state the gist of the first law of thermodynamics – the conservation of energy law – and describe several forms of energy. Can describe an example of energy changing from one form to another. For students: Have worked with heat and temperature measurements before, and are familiar with the atomic nature of matter. Have defined and worked with density and have worked with the concepts of mass, motion, gravity, and unbalanced forces.
Safety
The burning punk and the burning candle are the biggest dangers in this exercise.
To avoid burns, avoid setting fires, and avoid inhaling too much smoke, the burning punk and the burning candle must be kept under control and handled carefully at the lab stations, not carried around the room while burning.
The convection tubes and related equipment are plastic, not glass, and there are no chemical substances besides water, air, and smoke, so goggles are not necessary.
Engage
Twenty minutes for demonstrating a candle flame and having students depict the heat transfer processes on a diagram.This leads to the general focus question: Can you see convection happening in the air?The more advanced question is: What variable, at what setting, will make convection occur?
Explore
Thirty minutes. Start by asking what the effect of a cold base will be on the air in a convection tube, and what the effect of a warm base will be. Ask the students to predict the effects and explain how those effects will occur. If they predict the air will turn colder over the cold base, ask them to explain what will be happening to the molecules of air to cause them to become colder. If they predict the air will turn warmer over the hot base, ask them to explain what will be happening to the molecules of air to cause them to become warmer.
Safety Tips:
- Roll up loose sleeves and tuck in loose clothing. Tie back long hair.
- Do not let the burning punk touch the cylinder. The plastic cylinder will melt if it does.
- Have the instructor/facilitator light your punk at your station when you are ready. Do not carry a burning punk away from your station.
- Do not reach across an open flame.
- DO NOT LET THE CANDLE BURN FOR MORE THAN 1 MINUTE INSIDE THE CONVECTION TUBE. The plastic will get hot, and ultimately could start to melt and cause burns if people touch it.
Conduct exercise 4.1 from Catastrophic Events. Answer and discuss as a group reflection 1, A-D. Proceed to exercise 4.2 from Catastrophic Events. Afterward, answer and discuss as a group reflection 1, A-E.
Now ask to for predictions on what will happen if the two convection tubes are connected. Proceed with exercise 5.1, and have participants complete Student Sheets 5.1a and 5.1b. Discuss Reflection 1 as a group.
Explain
Fifteen minutes. Have students think, pair, share their best explanations. (1) How did the air in the cold-base tube get cooled? Was it by convection, conduction, or radiation, and what is the reasoning? (2) How did air in the warm-base tube get warmed? Was it by convection, conduction, or radiation, and what is the reasoning? (3) Did the two tubes connected together, one cold base and one warm base, for a complete convection cell? Explain.
Extend/Elaborate
Fifteen minutes. How does heat get transferred during a thunderstorm? A hurricane? In the earth’s mantle? What is the source of heat in each case? What are some results of the heat transfer?
Evaluate
Fifteen minutes.
Refer to the diagram above to answer the following questions:
- Why does the warmer water rise?
(Your answer should involve an intensive property of the water and a force.)
- Why does the cooler water sink?
(Your answer should involve an intensive property of the water and a force.)
- Does any heat energy radiate from the blue flame in the diagram?
- If any heat energy radiates, is it still heat energy while in the form of radiation? Explain your answer.
- How does heat get from the outside bottom of the pan, where the flame is touching, to the inside bottom of the pan, where the water is?
(Namethe heat transfer process, and describe how that type of heat transfer works.)
Standards Associated with Each Assessment Question
Questions 1 and 2: NSES-S.5-8.B.3, NSES-S.9-12.B.5, NSES-S.9-12.B.6, WA EALR 4 6-8 PS3A, WA EALR 4 6-8 PS3B, WA EALR 4 9-11 PS3A.These questions are about how convection works. A full understanding requires knowledge of the intrinsic property of density and the unbalanced gravitational force of buoyancy, which is why that knowledge is assumed prior to the exercise.
Questions 3 and 4: NSES-S.5-8.B.3, NSES-S.9-12.B.5, NSES-S.9-12.B.6, WA EALR 4 6-8 PS3A, WA EALR 4 6-8 PS3B, WA EALR 4 9-11 PS3A, WA EALR 4 9-11 PS3D.These questions are about radiation of heat energy, which involves transformation of heat energy into electromagnetic energy. Radiation, as one of the three mechanisms of heat transfer, is grouped with conduction and convection in physical science standards.
Question 5: NSES-S.5-8.B.3, NSES-S.9-12.B.5, NSES-S.9-12.B.6, WA EALR 4 6-8 PS3A, WA EALR 4 6-8 PS3B, WA EALR 4 9-11 PS3A.This question is about conduction of heat energy. Conduction, as one of the three mechanisms of heat transfer, is grouped with radiation and convection in physical science standards.
Note: One could also set up scenarios and ask questions about the role of convection during thunderstorms, hurricanes, and mantle flow/plate tectonics. Such questions would be designed to assess outcomes with regard to standards NSES-S.5-8.D.1, NSES-S.9-12.D.1, WA EALR 4 6-8 ES 2B, WA EALR 4 6-8 ES 2F, WA EALR 4 9-11 ES 2A, WA EALR 4 9-11 ES 2B.
Note: For climate change and the “greenhouse effect,” a number of scenarios could assess student knowledge of the fundamentally important roles of radiation and convection from the sun to the earth and within the earth system. However, several steps of learning progression would be needed beyond the exercises here for students to be able to apply knowledge of heat transfer to climate science.
Performance
Rubric for Assessing Student Performance
Activity / Science Standards / Excellent(100%) / Acceptable
(75%) / Unacceptable
(0–50%)
Knowledge:
Formative
Assessment / NSES-S.5-8.B.3, NSES-S.5-8.D.1, NSES-S.9-12.B.5,
NSES-S.9-12.B.6, NSES-S.9-12.D.1 / Participated in and completed candle flame diagram, spoke aloud to rest of class to explain how convection applies to an earth processes such as a hurricane or mantle flow. / Either did not complete candle flame exercise but spoke aloud to rest of class about convection in earth systems, or did not speak aloud to rest of class about convection in earth processes, but did complete candle flame exercise. / Did not complete candle flame exercise and did not speak aloud to rest of class about convection in earth processes.
Knowledge:
Summative
Assessment / NSES-S.5-8.B.3, NSES-S.5-8.D.1, NSES-S.9-12.B.5,
NSES-S.9-12.B.6, NSES-S.9-12.D.1 / Student answered all assessment questions completely and correctly. / Student answered assessment questions (1, 2) on convection correctly. Student answered questions (3-5) about other heat transfer processes partly correctly. / Student answered convection questions (1, 2) partly or not at all correctly. Student answered questions (3-5) about other heat transfer processes partly or not at all correctly.
Skill:
Conduct of Experiment / NSES-S.5-8.A.1,
NSES-S.5-8.A.2,
NSES-S.9-12A.1
NSES-S.9-12A.2 / Conducted all experiments safely, not moving any flames or smoke sources from bench, burning neither a student nor a convection tube.
Set up equipment correctly.
Completed predictions before conducting experiments.
Wrote in reflections sections and participated in class discussions of reflections.
Made observations and kept notes of them. / Conducted all experiments safely, not moving any flames or smoke sources from bench, burning neither a student nor a convection tube.
Set up equipment correctly.
Failed to complete one of the following, and completed the rest:
Completed predictions before conducting experiments.
Wrote in reflections sections and participated in class discussion of reflections.
Kept notes of observations. / Did not conduct all experiments safely—moved smoke or flame away from bench, or burned a student, or burned a convection tube.
AND/OR
Did not set up equipment correctly, and so could draw no answers from experiment about inquiry questions.
AND/OR
Failed to write reflections and did not keep notes of observations.
Extend and Apply your convection lesson
Science Content Question 1:
In what catastrophic earth system events is convection important?
Science Content Question 2:
If a lake in the summer time has warm water at the surface, cold water down below, will it spontaneously undergo convection? Why or why not?
(Hint: make a diagram of the lake looking sideways at the warm water layer on top, the cold water underneath, then think about it.)
Science Content Question 3 (Extremely Advanced):
Every sunny summer afternoon the air next to the ground has been warmed by conduction of heat from the ground. Why does this warm air layer right next to the ground not always convect? (In other words, why does this warm layer of air next to the ground not always rise upward in the atmosphere, carrying heat with it as it rises?)
Pedagogy Questions:
Now think about teaching.
- Did using convection tubes in today’s lesson help you understand convection?
What were some problems that reduced how much you learned?
- How would you use convection tubes to help teach convection to 6th-graders differently than was done in today’s lesson?
- Did today’s lesson help you understand how convection is important in earth catastrophes (hurricanes, volcanoes, etc.)?
National Science Education Standards-Students (NSES-S)
NSES-S.5-8.A.1 andNSES-S.9-12.A.1- STANDARD: Science as Inquiry -- As a result of activities in grades 5-12, all students should develop abilities necessary to do scientific inquiry
NSES-S.5-8.A.2 andNSES-S.9-12.A.2- STANDARD: Science as Inquiry -- As a result of activities in grades 5-12, all students should develop understandings about scientific inquiry
NSES-S.5-8.B.1 STANDARD: Physical Science -- As a result of activities in grades 5-12, students become familiar with the idea that energy is an important property of substances, that most changes involve energy transfer, and experience many kinds of energy transfer.
NSES-S.9-12.B.5 - STANDARD: Physical Science -- As a result of activities in grades 9-12, all students should develop an understanding of the conservation of energy.
NSES-S.9-12.B.6 - STANDARD: Physical Science -- As a result of activities in grades 9-12, all students should develop an understanding of interactions of matter and energy.
NSES-S.5-8.D.1 STANDARD: Earth and Space Science – Structure of the Earth system.
NSES-S.9-12.D.1 - STANDARD: Earth and Space Science – Energy in the Earth system.
Washington State K-12 Science Education Standards 2008
WA EALR 4 6-8 PS3A STANDARD: Physical Science – Energy, energy transfer, and energy transformation
WA EALR 4 6-8 PS3B STANDARD: Physical Science –Heat and heat transfer: conduction, convection, and radiation
WA EALR 4 9-11 PS3A STANDARD: Physical Science –Energy transfer and energy transformation
WA EALR 4 9-11 PS3D STANDARD: Physical Science –Energy transfer in waves and interaction of energy waves, including electromagnetic waves (radiation), with matter
WA EALR 4 6-8 ES 2B STANDARD: Earth and Space Science –Energy transferred from sun to earth systems, role of uneven heating of earth in driving air and ocean currents
WA EALR 4 6-8 ES 2F STANDARD: Earth and Space Science – Convection in the mantle and plate tectonics
WA EALR 4 9-11 ES 2A STANDARD: Earth and Space Science – Global climate and the role of uneven heating by sun/hotter and colder parts of earth in determining regional climates
WA EALR 4 9-11 ES 2B STANDARD: Earth and Space Science – Energy transfer mechanisms in earth’s climate system; role of greenhouse gases and radiation in global climate
Supplemental Information
Background on Student Knowledge of Convection
Few studies have been published on how students understand convection and heat transfer. See Atlas of Science Literacy, vol. 2, p. 24, box in right-hand column, for a discussion andreferences on student knowledge of heat, temperature, energy transformation, and energy transfer. Also see Making Sense of Secondary Science: Research into Children’s Ideas, Chapter 19, “Heating,” p. 138-142.