Methods of Heat Transfer
Number of Learners: 90 Students
Grade (or Age): 8th grade
School/Town: Timilty Middle/Roxbury
Estimated Length of Session: 60 minutes
Curriculum Area: Science (Chemistry)
PREREQUISITE KNOWLEDGE AND SKILLS
Students have an understanding that heat can move from one place to another as well as a general familiarity that certain materials reduce this transfer (e.g. coats keep body heat in).
CONTENT TO BE TAUGHT
This lesson plan is meant to help illustrate and further understanding of the different methods of heat transfer (particularly conduction) and the role insulators play in the process.
The guided-inquiry portion of the lesson plan allows for students to connect methods of heat transfer like conduction, convection and radiation to a common item in their lives: the use of hats. Students are introduced to the concept that the design (style) of hats affect the heat transfer between the head and the environment differentially. The experimental portion of the lesson examines the way the material composition of a hat affects the rate at which heat transfers from inside a hat to the environment and how water effects the insulating properties of a substance.
It fulfills at least one of the Massachusetts Frameworks Physical Science (Chemistry), Grades 6–8 curriculum standards: 14. Recognize that heat is a form of energy and that temperature change results from adding or taking away heat from a system.
A number (N) of knit hats of various material (at least three: e.g. wool, acrylic, cotton) and different types (knit toboggan; visor; cowboy, straw or other sun hat).
N (or more) thermometers
N large test tubes (with rubber stoppers)
2*N rubber bands
Large amount of water (some of which should be kept at room temperature)
Heat source to boil water
Access to a refrigerator of some sort to speed cooling
Begin heating a large amount of water to near the boiling point.
Conduct beginning class work. Make sure that students bring up both hats aimed at warmth (like toboggans or Russian hats) and hats meant for shade (baseball caps, visors, straw, cowboy hats).
Pass out worksheets for the students to go through as they conduct the experiments.
Place rubber caps with thermometers through the middle on test tubes filled with hot water (or place solid rubber caps and have the thermometers between the outside of the test tubes and hats). Wrap test tubes in hats (socks would work equally well; wet or dry at room temperature) of various materials (wool, acrylic, cotton).
Have students predict: which will cool the fastest? slowest?
Ask: What if we soaked the hats in water? Would they cool faster or slower (i.e. does water make the hats better or worse insulators)?
Conduct Experiment. Students may also be required to plot the data on a simple Cartesian coordinate map plotting time vs. temperature in both conditions. Inquire about results: did heat transfer (dissipate) more quickly or less quickly when the hats were wet with room temperature water? Students may be asked to compare results with other groups using hats of different material.
Explain that: Heat is another word for the average speed of movement of particles (or molecules). The faster molecules move and bump into each inside of a thing, the warmer something is. An insulator is a material that does not transfer heat very easily (for instance, wood or rubber). A conductor does transfer heat very easily (silver or aluminum)…
There are three processes by which heat is transferred called: Conduction, convection, and radiation. Conduction occurs when two things (can include a liquid or gas) come into direct contact with one another and the molecules in one bounce into the molecules in the other. Convection occurs when currents in a liquid or gas (sometimes a solid) carries the molecules to somewhere else (for instance, imagine a hot swimmer in the ocean, the currents could carry his body (with is warm) someplace else). Radiation occurs when energy is transferred to molecules without the need for anything to transfer the energy (e.g. the light from the sun can make things hot but there are no molecule in outer space to carry the light here).
What other context might heat transfer be important? Sunburns, cooking things on stove, burn your hand from the steam on stove, refrigerator...
Which of these processes do you think is the most important in the experiment? Conduction: the molecules that are moving fast in the hot water, bump into the molecules of the test tube, which bump into the thermometer; changing its temperature.
How might each of the other types of heat transfer be occurring in the experiment? Radiation: the light from the room is hitting the hats and heating it from the outside. Convection: (difficult question) when you move the thermometer around to check the temperature it is carrying the heat from the thermometer to another location in space.
What types of heat transfer do the different styles of hats we mentioned in the beginning class work hope to address? Sun hats hope to limit radiation from the sun, baseball caps are different from visors because visors allow for conduction to occur more easily on the top of the head (visors let heat out of the top of the heat easier than baseball hats). Warm hats aim to slow down the conduction from the head into the cold environment. What material would be the best to make these hats out of, based on our experiment? Cotton is best for baseball hats because the heat from your head can dissipate (spread out) into the environment more easily. Wool is best for cold weather hat because it doesn't allow heat to dissipate from your head very easily.
Students are required to record data for temperature measurements and answer some preliminary questions for the experimental section. Additionally, student responses can be gauged during both the beginning class work materials and the closing section questioning.
Students can be asked to do additional research into one of the types of heat transfer and give a brief presentation about their results. Students can be asked to describe all three types of heat transfer in various situations (cooking on an outdoor stove).
Appendices for Heat Transfer Lesson Plan