Effect of Soil Moisture on Temperature Laboratory Experiment

Goals/Outcomes

1. Use a thermometer and an infrared gun to measure and compare the temperature of dry sand and moist sand over a period of time.
2. Measure the surface temperature of different surfaces and compare the results to those in the lab activity.

Assumptions About Prior Knowledge

Student has some understanding of:

• Specific heat
• Sensible heat
• Latent heat

NOTE: As part of the teaching box, lab activities that demonstrate these two concepts have been included as an appendix “Heat and Temperature Concepts”.

Teacher Preparation

1. Make copies of the lab directions and tables—one per student group. Master obtained at:
   
   http://space.hsv.usra.edu/TRESTE/papers/06_drought_files/soil_moisture_lab.doc


2. Set up the apparatus pictured in the lab handout (one per group of 2-3 students is ideal)
3. Materials needed (for each student group)
   • Ring stands
   • Water
   • Clamps to support lamps
   • Thermometer
   • Styrofoam cups (2)
   • Infrared gun
   • Sand
   • Incandescent light bulbs w/reflectors
   • Room temperature water
4. Identify locations for outside portion of the lab activity

Activities

1. Set up the experiment.
   Predict what the temperature will do in each cup.
   What difference do you expect between the thermometer and the infrared gun?
2. Conduct the experiment. Record data in the appropriate charts of the handout.
3. Discuss the results.
• What did you observe in the wet sand?
• What did you observe in the dry sand?
• What differences were observed between the temperatures obtained with the thermometer and the infrared gun?
• What accounts for the differences?
• Why did this happen?
• What would happen if a different colored surface were used?
(The temperatures in both cups should rise with the dry sand rising faster. Some of the heat energy on the wet sand is being used to evaporate the water (latent heat) instead of raising the temperature. The infrared gun is measuring the surface temperature while the thermometer is reading just below the surface.)
4. Have students repeat the experiment using dark soil instead of sand.
• What did you observe with the dark soil?
• What differences did you observe between the dark soil and the sand?
• What might account for the differences between the two experiments?
• Predict the temperatures you would find over different surfaces outside.
(Dark surfaces tend to absorb more of the radiation than the light-colored surfaces and should show a greater increase in temperature over the same time. If wet, dark soil was also used, the wet soil should show a slower increase because of latent heat used to evaporate the water.)
5. Student groups will record the surface temperatures over five different surfaces outdoors.
• How did your observations compare with your predictions?
• How can you explain the differences?
  (Darker surfaces exposed to the sun should show the highest temperatures.)

Assessment

1. Completed lab sheet
2. Answers to questions—written or oral
3. Revisit the original problem sheets to see if there are changes—additions, corrections, deletions.