Lesson 2: The roles of pressure and differential heating in wind

Activity 2. Differential heating of land and water from solar radiation

This activity illustrates how dark land surfaces, light land surfaces, and water all heat at different rates. Students will learn that water heats more slowly than land and therefore the surface of the Earth heats at different rates, causing our weather.

Online Resource: Which Gets Hotter, Land or Water http://www.teachingboxes.org/catalog.jsp?id=DLESE-000-000-004-574

Materials:

• 3 identical waterproof containers (1–2 cup size plastic containers, U-shaped dishes, large Styrofoam cups, etc.)
• 3 thermometers
• Large reflector lamp and ring stand with at least a 100-w bulb
• Black or dark brown sand, white sand and water, all at room temperature. The sand needs to be dry.
• Stop watches or a large clock with second hand

Advanced Preparation:

Read through the procedure before class; gather the materials for the student activity together

Time needed: Teacher Prep - 15 minutes; Class activity - 90 minutes (Teacher tip: if you don’t have block scheduling, try 30 minutes of heating and 15 minutes of cooling)

Procedure:

Introduce the concept of solar radiation and differential heating and cooling of land and water by asking if anyone has ever walked barefoot on the beach on a sunny day. What did they notice about the temperature of the dry sand as they walked along the beach and in and out of the water? Which material felt warmer? (Dry sand) Which material felt cooler? (The wet sand and the water, which is why we go in to cool off!) Why? (An example, wet sand: The sun’s energy goes into evaporating the water in the sand before it begins to actually raise the sand's temperature.)

In this activity, students will use water (at room temperature), light soil, dark soil, and a reflector lamp to explore how, even at a small scale, water heats up much more slowly than land. Students will measure the temperature of the heating and cooling of each material in Celsius every 5 minutes for approximately 70 minutes. Then they will graph their results.

1. Print out the activity, “Which Gets Hotter: Land or Water?” http://www.teachingboxes.org/catalog.jsp?id=DLESE-000-000-004-574 for yourself. It comes with teacher instructions and student procedures and worksheets. Make copies of the student procedures and worksheets for your class.
2. Have the students follow the instructions to set up the activity.
3. Divide the students into groups of 2 or 4.
4. Check the set up of each team's equipment to make sure set up is correct (most importantly that the heat source is directly over all three cups evenly!). Make sure each group has a reliable timekeeper and that they all know how to read the thermometers.
5. The students follow the student procedures to measure the temperature of the heating and cooling of each material in Celsius every 5 minutes for approximately 70 minutes.
6. Get the students started on creating their graphs by drawing on the board a large example graph with time on the x axis and temperature on the y axis.
7. Discuss the questions on the worksheets with your students.

Closing the activity: This activity may lead to a discussion about how continents will be warmer than oceans when heated by the sun. This is a good lead in to the next lesson where you explore high- and low-pressure centers due to the temperature differential between land and water.