TOPICS:  Heat transfer, Bernoulli's principle

LEVEL:  High school

TIME:  This activity can be done as a class on school grounds or assigned as a homework project.  Allow enough time for students to have film developed, pictures mounted, and so on.

ADVANCE PREPARATION:  Collect ski or other outdoor magazines for class use. You may wish to take photographs yourself to illustrate the answers to the discussion questions.  Student displays which are particularly well done can be saved and added to your collection .

PREDICTION: In class discussion, encourage creative, logical, and critical thinking. We recommend that you introduce the following ideas if they are not suggested by students:

Warm sports are typically found next to buildings and other heat sources, water, trees and other dark objects. The ground is a heat source in winter; frost spots are typically found on objects not in good thermal contact with the ground, such as automobiles, bridges, tree twigs, grass, and windows. Snow drifts are often found on the downwind side of fences, and just inside wooded areas. Snow scours are often found at building corners.

QUESTIONS 2-10 require higher order thinking skills.  We recommend that you discuss these questions in class before students write out their answers. Other questions relating to heat transfer may be found in the Winter Hot Spots activity .

2. The sun, being low in the sky in winter, will not shine on the north-facing side.  Therefore, snow melts there last .

3. Road surfaces have contact with the ground, a good heat source.  Bridges have far less thermal contact with the ground .

4. Clouds reduce the heat loss due to radiation .

5.  On humid days, water will condense on the snow releasing considerable latent heat which goes into melting.  For every gram of water condensed, enough heat is released to melt about 7 grams of water .

6. The visible wavelengths of sunlight can pass through the window to heat the cat, but infrared radiation from the cat cannot be transmitted out the window.  Window glass is opaque to thermal infrared radiation .

7. As the wind passes over the edge of the roof, it slows down and deposits the snow it is carrying .

8. The trees slow down the wind, causing the snow to drop forming a drift .

9. Wind speeds up as it passes through constricted openings in the snow fence or passes over the fence.  High speed wind can carry more snow than low speed wind.  The wind slows after passing through the openings and deposits snow downwind .

10. The wind passing over the top of the dune speeds up, thus picking up sand; this sand is dropped further downwind.  A fence on the upwind face of the dune slows the wind.