Where Did That Heat Flow Now?

Courtesy of National Science Foundation Polar Connections
http://www.nsf.gov/od/lpa/nstw/teach/nstw98/english/actc/heat1.htm

MATERIALS
RADIATION STATION

• reproducible "Discovery Card"
• 4 thermometers
• ball of string
• heat lamp
• meterstick or yardstick
• graph paper

CONDUCTION JUNCTION

• reproducible "Discovery Card"
• containers made of various materials (metal, wood, glass, plastic, Styrofoam)
• other natural-fiber items (fur, cotton, leather)
• wood and metal yardsticks
• electric light
• heat lamp
• small balls of wax, slivers of crayons, or chocolate chips
• oven mitt (optional)
• towelettes for clean-up

CONTEXT
All warm-blooded animals, including humans, can survive only in a very narrow range of internal body temperatures. For most, just five or six degrees too high or too low means the difference between life and death. Polar animals have adapted to survive extreme temperatures at the poles by insulating and more efficiently using the body heat they generate in a wide range of ways. To begin their exploration of these forms of "polar protection," students will first realize the science underlying the flow of heat.

PREPARATION

• Make two copies of each Discovery Card and cut them out. Then place one thermometer away from obvious heat or cold sources. It should register room temperature.
• Create four science stations: two "Radiation Stations" and two "Conduction Junctions," equipping them with the materials described above. Make sure the containers and other items for Conduction Junction stations have been in the room where you'll conduct the experiments at least overnight.

PROCEDURE

1. Start by asking open questions:
   • What special challenges do animals (including humans) living in polar regions face?
   • How do they lose or gain heat?
   • How do they protect the heat they generate?
   • Why do they need to protect it—where does it go?
   • How could you track its flow?
2. Discuss:
   • How do we know that heat exists at all?
   • What senses do we use to detect heat?
   • What is the difference between heat and temperature? (Measuring temperature is one way we use to measure hotness and coldness—in other words, heat intensity. Remind students that there is some heat energy present even at very low temperatures.)
3. Divide the group into four science station teams and talk through the experiments described in the Discovery Cards. Have teams make predictions as to what will happen. Give teams 15 minutes to complete the Discovery Card at their stations; then have them switch to the other station. (You may have to help younger students a bit.) Each team should assign a member to record results and answers to the questions in a notebook. Finally, challenge each team to draw a heat graph from the Radiation Station data. The graph can be a pictorial "isotherm" map (which looks like a topographical map) with the heat source in the middle, or it can be a simple bar graph showing temperature and distance from the heat source.
4. At both stations, heat flows from one location to another. Ask:
   • What is the evidence that heat is flowing?
   • How does heat flow differently at the two stations?
   • Compare each team's graph for the Radiation Station. What patterns or interesting points do students observe?
5. Assuming all of the Conduction Junction containers and other items have been in the room long enough (overnight would suffice), they will all be the same temperature—room temperature. So why do they feel different to students' touch? Some materials, such as metal, allow heat to flow faster from your hand, leaving your fingers feeling colder. Other materials, such as Styrofoam, reduce the heat flow; your hand feels the same. Challenge students to hypothesize why. Ask which is warmer to begin with: their hands or the containers? Can they come up with a general rule for the direction in which heat flows? (From warmer to cooler areas. The feeling their hand gets depends upon the rate of conduction permitted by each material.)

ASSESSMENT
Ask teams to consider and explain some household examples of heat flow. For example: Which would make a bathroom feel hotter—if you filled the tub with hot water, or just the sink? Why? (The tub, because of the greater surface area and amount of water.) Or: When stirring a pot of boiling noodles, should you use a wooden spoon or a metal one? (The wooden spoon conducts heat less readily.)

EXTENSION
In what ways have polar animals adapted in order to control the flow of heat? Challenge teams of students to research and identify as many different strategies as possible, such as the following:

• Wood frogs of the Arctic are able to freeze solid, thaw, and survive. But they have adapted to avoid having to do so. Their blood contains a protein that lowers the frog's freezing temperature. Students can design an experiment to test "anti-freezes" such as salt, dirt, sugar, and rubbing alcohol in an ice cube tray. Which additives most efficiently prevent freezing?
• Smaller polar birds shiver through the cold polar winters. How does shivering warm you up? (Muscles generate body heat when they "fire" or move.) Experiment: Does exercising increase your body temperature? What other body defenses or effects does it trigger?