Heating Land and Water

Objectives: To study different heating characteristics of water and land

Introduction
One of the keys to understanding weather and climate is learning about the difference in the way that water and land heats up and cools off. The purpose of this lab is to help you understand this difference.

Materials

lamp with support stand, two small cups, sand, water, paper towels, wooden slats, short plastic thermometers, clothespin or clip, stopwatch or clock with a second hand and data table, graph paper, textbook.

Procedure

1. Set up the apparatus as instructed.

2. Fill the water container about three fourths full and find the mass (Tare with empty cup first). Use an equal mass of sand. If the sand isn’t at least 2 cm in height, add more of both sand and water. Place the two cups 10-15 cm below the base of the lamp so that they will receive equal light. Use the wooden slats so the levels will be the same. The bottom of the probes/thermometers should be about 1 cm below the surface of the water and sand. Do not turn the light on yet.

3. On a separate sheet of paper, design a data table so that you can record the 21 temperatures for each container. Record the temperatures of both thermometers BEFORE the light is turned on. Record this on the data table in the space for “0” (zero) time.

4. Switch on the lamp and record both temperatures every 60 seconds for 10 minutes

5. Shut off the light, and move it away from the containers because the lamp will continue to give off heat after it is turned off. Continue to record the temperatures every 60 seconds for another 10 minutes.

6. Plot your data (or print your graph). Label one line “water”, and the other “land”.

Questions

1. During your lab, which heated up the fastest, the land (sand), or the water? Justify your answer by comparing the lines on your graph.

2. Which cooled the fastest once the light was shut off? (Look at the graph again.)

3. According to your text water has a high specific heat. How does this lab show that?

4. Air in the troposphere (bottom layer) is heated from the bottom up by heat given off by the surface. If the sun shines equally on San Diego and Phoenix, AZ, which would get hotter during the day? Why do you think so?

5. Based on the results of your lab, which of the two cities would probably have a bigger difference between its day and night temperatures?

6. Anchorage (southern coast of Alaska) is several hundred miles north of Helena, Montana yet its January temperatures are similar to Helena’s. Explain why.

7. Most texts have maps that shows average January and July temperatures. Use the map in your text to find 3 of the warmest places during each of those months. Write them down below (e.g. southern Africa, central North America, northern Ireland etc.):
January:

______

July:

______

8. Are they on land or water? Based on the results of this lab, is that what you would expect? Explain

9. On the January map do the isotherms in the N. Hemisphere bend northward or southward as they go from ocean to land? ______

This means that in the winter, areas over land are (Circle one): . . .warmer . . . colder

10. Which regions tend to have a greater difference between summer and winter temperatures, areas close to oceans, or areas far from oceans?

11. What have you learned from doing this lab?

Heating Land and Water – Teacher’s Notes

Intoduction
One of the most important concepts that students should learn about in the study of meteorology/climate is that continents and oceans heat up and cool off differently. Understanding this difference is crucial to learning about daily and seasonal changes that impact weather and climate. The “Heating of Land & Water Lab” helps students learn and remember this important concept. The students will be recording the temperature of the materials as they are heated beneath a light for 10 minutes and also monitoring them as they cool in the 10 minutes after the light is removed.

Materials
Each lab group will need the materials shown in the photo above: a lamp (we use 75, 100, 150, or 200 watt bulbs), a ring stand or other support stand for lamp, two 8 oz. cups, dry sand, water, stopwatch or clock with a second hand, two small thermometers, (Use short thermometers so they won’t get heated directly by the light. The cheap plastic ones we use are alcohol-based and available at scientific supply houses).

Note: Graph paper copies best (if at all) by using the darkest setting available.

Set-Up
Place the two cups 10-15 cm below the base of the lamp so that they will receive equal light. They should be filled to the same amount. The bulb of the thermometers should be about 1 cm below the surface (of the water and the soil) The clothes pin will hold the thermometer in the water in place. If the surface students will be working on is dark, run the experiment over a neutral- colored surface (like a wooden slat). Have paper towels available for spills.

Typical Results
The temperature of the soil will rise from about 27 C to 43 C while the light is on (depends a lot on the power of the light bulb used ). The water (tends to be cooler than the sand if gotten directly from the tap) will go from about 25 C to 33 C. After the light is shut off, the water will lose only a few degrees (it may stay essentially the same for the first one or 2 minutes. The sand will cool to a lower temperature than the water, however it won’t reach its starting temperature in the 10-minute cooling period.

The map referred to in Questions 7 and 8 is on page 464 in your text.

Your notes here: