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Heat Transfer
Lesson Plan
Content Areas: Science, Art, Weather, Engineering Goals:
- Students will understand how to visualize and explore the three types of heat transfer: conduction, convection, and radiation.
- Students will understand and conceptualize how heat energy flows from place to place, always flowing from warmer to cooler substances until the temperature of both substances is the same (equilibrium).
- Students will understand how various factors affect heat transfer, including temperature differentials, duration of contact, surface area, and type of material.
- Students will understand how to visualize and explore heat transfer through sketches and drawings as they find ways to stay cool in a heat wave or warm in a blizzard. Background and “Big Picture” In our daily lives, we use the word heat in several ways. For example, we might use it as a verb, such as when we heat the oven to bake brownies, or we might use it as a noun to describe the warmth of an object, like when we feel the heat of a fire. In science, heat is the energy that makes molecules move. Molecules with more heat energy move faster and spread further apart than molecules with less heat energy. A key point to remember is that heat energy always flows out of a hotter substance and into a colder substance. Heat keeps flowing until the objects reach the same temperature (equilibrium). Heat transfers faster between objects with greater temperature differences. Likewise, larger areas of contact (surface area) and longer times (duration) of contact lead to faster heat transfer. The type of materials involved also affect the rate of heat transfer (conductivity). Heat energy moves from place to place in three ways: conduction, convection, and radiation.
Figure 1. Example drawings of the three types of heat transfer. Conduction refers to how heat energy moves by direct contact with objects that are touching. Some materials, like metals, are more conductive than other materials, which is why we cook with metal pots, which conduct heat rapidly to the food inside, but stir hot food with a wooden spoon, which conducts heat poorly and keeps us from burning our hands. Convection refers to how heat energy moves in a fluid like water or air. Warmer fluids are less dense and rise up. Colder fluids are more dense and sink from the pull of gravity. We can see convection clearly in a lava lamp: as the base warms the fluids (wax and water) above it, they get less dense and rise up, until they cool, become denser again, and fall. Radiation describes how heat moves through space. It is electromagnetic energy, such as the visible and ultraviolet light moving as waves from the sun. If you have ever had a sunburn, you have felt ultraviolet waves transfer heat energy from the sun to your skin. Understanding heat transfer is essential for atmospheric scientists, who use it to predict weather patterns. Mechanical engineers also use this concept to design cooler car interiors. And urban planners use it to design shadier sidewalks in cities. Age: This lesson plan can be adapted for students ages 6 to 18 and older. Duration: This lesson plan takes about 60 minutes. Materials:
- A flat metal material made of aluminum, stainless steel, copper, or other metal.
- A similar sized material made of carpet, cloth, fabric. o The more similar the materials appear to be, the more effective the demonstration. For example, the same size square, the same thickness, etc. o The activity works best if these materials have been sitting at the same room temperature for at least 2 hours. Avoid heat or light sources.
- A matching set of black and white objects (made of the same substance, either both ceramic tiles or both cloth, etc.)
temperature of the metal (cooler than body temperature). Heat still flows from your finger to the cloth or other object(s) as long as they are in contact, it just happens so slowly you do not notice it as much. Metal has a high thermal conductivity. This property makes it good at transferring heat, which is why it is useful for cooking (transferring energy as heat from flame to food). Air has a low thermal conductivity. Objects that contain air (carpet, insulation, down feathers, wool sweater) trap air that impedes heat transfer. These materials are called thermal insulators. *Remind students to revise drawings or make new ones to describe what they see/learn/think. Then ask them to show-and-tell what they drew. d. Instruct students to touch the metal for longer periods of time to see what happens. Instead of the brief split-second of touch, try touching the metal with your fingertip for 10 or 20 seconds. What happens now? Answer: The heat from your finger warms up the metal, and your finger cools off. The longer you are in contact, the more energy that transfers. Eventually, your finger and the metal reach the same temperature. Once the temperature of the two objects is the same (i.e., the temperature difference is zero), heat transfer stops. *Remind students to revise drawings or make new ones to describe what they see/learn/think. Then ask them to show-and-tell what they drew. e. Now have students place their whole hand on the metal. What happens now? Answer: Clearly, more heat is transferred from your whole hand to the metal than when you touched it with just your fingertip. It is faster to use your whole hand to warm up the metal than to use just your finger. As the area of contact increases, the total energy transfer increases. *Remind students to revise drawings or make new ones to describe what they see/learn/think. Then ask them to show-and-tell what they drew. PART II. CONVECTION INQUIRY & CONCEPTUALIZATION (10 minutes)
1. SETUP - Turn on a lava lamp about 30 minutes before the lesson starts (or longer if the lamp has been sitting in a cold room). If you do not have a lava lamp, show a YouTube video such as https://www.youtube.com/watch?v=xB5FUYNXt9c.
2. CONSIDER & DRAW - Observe what happens to the fluid inside the lava lamp and make a quick sketch (~1 minute) describing what is happening. Ask questions to encourage students’ thinking. a. Why does the blob rise and fall? Answer: The waxy blob rises and falls because of convection , which refers to how heat energy moves in a fluid. The lamp at the base heats up and warms the colored fluids (wax and water). The fluid contains a waxy material that changes when the temperature changes. At warmer temperatures, the waxy fluid gets less dense and rises upward. As it gets farther from the heat source, the waxy blob cools down, gets more dense, and falls down from the pull of gravity. b. How might this type of heat transfer (convection) relate to weather? Answer: Warmer surfaces on the Earth transfer heat energy to the air they touch by conduction. That warm air rises, then cools at higher altitudes, then falls again, creating up and down convection currents. *Remind students to revise drawings or make new ones to describe what they see/learn/think. Then ask them to show-and-tell what they drew. PART III. RADIATION INQUIRY & CONCEPTUALIZATION (10 minutes) 1. CONSIDER & DRAW -- Introduce this activity by placing matching black and white colored objects, such as ceramic tiles or cloth, in the sun (or under an incandescent light bulb) for a few minutes. Observe what happens and make a quick sketch (~1 minute) of the experience. Ask questions to spur students’ thinking. a. Which surface feels warmer? Answer: The black surface feels warmer than the white surface because, through radiation , it absorbs all of the wavelengths of visible light. White surfaces reflect visible light, which is why they look white. When you touch the black surface, the temperature is hotter (it absorbed more radiation ), so heat transfers by conductance to your finger from the hotter black object, more than that from the cooler white object. b. How might radiation from the sun affect the weather? Answer: The sun transfers heat as electromagnetic radiation to the Earth’s surface, warming the ground, oceans, buildings, roads, etc. By conduction, these warmer surfaces transfer heat energy to the air they touch. That warm air rises, then cools at higher altitudes (like the convection in a lava lamp), then falls again, creating up and down convection currents. There are always colder and warmer areas on the Earth’s
● Panels can show different time-frames or sequences. ● Arrows can show things going in and out or changing from one thing to the next. ● Color can show temperature differences (warm or cool colors); dark and light colors push things back or bring things forward. ● Lines, texture, and repetition can represent motion or diagram a system. ● Text can clarify intended meaning. Visualizing ideas and thoughts serves to build and demonstrate understanding. --it allows us to apply complex scientific concepts in new ways --it helps us explore alternate perspectives --it helps us explain the concepts to others -- we learn better by teaching others Evaluation: There are several ways to evaluate learning from this lesson. For example, look at students’ drawings to explore their thinking. Ask them to explain what they drew. If needed, explore misconceptions by asking guiding questions to push their thinking toward accuracy. Another way to evaluate learning is to have students free-write about conduction, describing how heat energy flows between two objects. You could create an art exhibition where students can show-and-tell their ideas for staying cool in a heat wave or warm in a blizzard and teach each other about the science. You could ask students to design a home that requires less energy to stay cool in summer and keep warm in winter in places where outside temperatures vary greatly. Modifications : Adjust the vocabulary and assessment to match grade level and content area. Resources:
- Khan Academy: https://www.khanacademy.org/science/physics/thermodynamics/specific-heat-and- heat-transfer/v/thermal-conduction
- Physics.org: https://phys.org/news/2014- 12 - what-is-heat-conduction.html
- Conduction in Weather: https://scied.ucar.edu/conduction#:~:text=Conduction%20in%20the%20Atmosphere,Ea rth's%20surface%20and%20the%20atmosphere.&text=Although%20sunlight%20warms %20the%20surface,the%20poor%20conductivity%20of%20air
Acknowledgements: This lesson was created by the Cool Science project, which is funded by the following National Science Foundation Grants: AISL-1906793, AISL-1906640, & AISL-
- Learn more at https://www.coolscience.net/.
