TOPICS: Survival, heat transfer, insulation
LEVEL: High school
TIME: 45 minutes
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MATERIALS:
Purchase cotton denim, other cotton like flannel, and wool yard goods. Try to obtain fabrics of comparable thickness. Use Celsius thermometers if possible. A covered plastic bucket can be used to hold hot water for the class. Point out to students that the water being used is much higher than body temperature. This activity is a demonstration of the comparative effectiveness and a higher temperature will assure results in a short time
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INTRODUCTION:
Obviously, the hiker pictured here is improperly dressed for winter weather. Question 10 below asks students to use the data from this activity to suggest ways to decrease the hiker's heat loss. You may wish to discuss this issue prior to the activity
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PREDICTIONS:
In class discussion, encourage creative, logical, and critical thinking. We recommend that you introduce the following ideas if they are not suggested by students: a loft or thickness of material is critical in determining effective or windproof covering over fabric enhances air trapping ability.
Layering clothing allows students to take advantage of best properties of each fiber and fabric. This experiment is qualitative rather than quantitative so keep a record of results from year to year to see the variability.
OPTIONAL DEMONSTRATION: Obtain a wool and a blue jean pant leg. At the beginning of the activity, soak both in water and wring them out. Hang them outside the window for 10-15 minutes while lab is underway. Pass the pant legs around the class, having students put their arms into the pant leg to experience the dramatic difference between the fabrics. The sleeve of a bulky sweater, a down or polyesther jacket, a sweatshirt, and similar items can be compared to each other and to the fabric squares to demonstrate the importance of garment construction (No need to remove sleeve from garment!) Various types of socks can also be compared
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PROCEDURE:
For a fair test, it is important to tell your students to be CONSISTENT with everything they do. They should fill the containers with the same amount of water at the same temperature and time. They should mist with cool water equally and fan all the cans together
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OPTIONAL STEP B & C:
You may want to have some students set the containers in a shallow pan of snow on the window sill outside.
QUESTIONS 3-11 require higher order thinking skills. We recommend that you discuss these questions in class before having students write out their answers
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3.
The control container is used to test the insulating effectiveness of fabrics in general
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4.
Wool
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5.
Evaporation of water increases the cooling rate, especially with cotton
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6.
Cotton denim or possibly other cotton. The uncovered container retains heat better than the one covered with wet cotton denim, because the uncovered container dries off faster.
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7.
Wind increases evaporation by bringing in new dry air as evaporation proceeds and air warmed by the body is replaced by cold air (wind chill)
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8.
You'd probably be better off wearing nothing than wet jeans in cold weather
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9.
The fabrics may differ in weight and thickness, texture (knit or woven), or tightness of weave
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10.
Dress in wool clothing; layer clothes to allow adding or removing clothes when cool or warm to reduce accumulation of perspiration moisture; wear a hat to reduce heat loss from head; wear long sleeve shirt and jacket, long pants for insulation; wear mittens. See "Avoiding the Big Chill: Clothing" for more information
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11.
Go with a partner; make sure someone knows where you are; take high energy snack; consult an experienced person before going into a new area. See "Avoiding the Big Chill: Winter Outings" for more information.