Differential Heating and Cooling of Land
All you need to do on a sunny day is walk on a dry beach in the
early afternoon to learn that the sand can get very much warmer
than sea water. Water is a slow conductor of heat, thus it needs
to gain more energy than the sand or dry land in order for its temperature
to increase. On the other hand, soil loses its heat much faster.
But your toasted toes would perhaps mislead your mind: Earth's oceans
are far more important than the land as a source of the heat energy
which drives the weather. Not only do the oceans cover more than
2/3 of the Earth's surface, they also absorb more sunlight and store
more heat. Additionally the oceans retain heat longer. The Sun's
rays also penetrate the oceans to a depth of many meters, but only
heat up the top layer of the sand or soil. Water has to lose more
energy than the sand (dry land) in order for the temperature to
During the summer the land is much warmer than the water. It's
made up of many different materials which absorb the Sun's rays
differently. Land covered in forests or snow warms and cools very
differently from a city blanketed with asphalt streets and concrete
buildings. Darker materials absorb more radiation than lighter materials.
Texture also matters. Rougher and dryer materials absorb more radiation
than smoother and wetter materials. If you have ever walked barefoot
on a street or sidewalk you'll recall these are much hotter than
the grass beside them.
This Activity can also be adapted to challenge older students to
come up with their own experimental protocols to test some of these
fundamental and important principles. As an extension, you can invite
students to suggest various materials to test other than those specified
Students will research, compare and contrast temperature patterns
around the country/world.
Students will observe that soil both heats up and cools faster
Students will observe that different colors absorb different
amounts of the Sun's radiation.
Provide temperature maps to each group of students (see p. 3 of
student handout). Allow time for them to study there maps and share
observations with each other. Then ask each team to prepare 3-5
generalizations they have gathered from the maps. Prompt them to
"Discuss the different temperature patterns you observe. Where are
the highest temperature located? Where are the lowest temperatures
located? Compare coastal temperatures with temperatures further
inland. Compare temperatures at different latitudes and elevations.
Record these observations on an overhead transparency, chalkboard
or large chart to facilitate whole class discussion.
Based on what they have observed on the temperature maps and from
their existing knowledge, challenge students to form a hypothesis
about whether soil or water will heat faster, and which will cool
- Reflector lamp with 100 watt bulb
- 2 x 250 ml beakers
- 150 ml of soil
- 150 ml of water
- 2 thermometers
- Temperature map (download current
maps here or see URL's below)
- Student Worksheet 1.2 (Side 1 supports the main Activity and
Side 2 the "Sports Shirt" extension.)
Distribute Student Worksheet 1.2 and review the procedure with
students. Ensure each group has all the materials required and understands
safety guidelines for the use of glassware and thermometers. Have
students place 150 ml of soil in one beaker and 150 ml of water
in the other beaker. They will then place a thermometer in each
beaker and record the starting temperature. Ensure they position
the lamp 10 cm from the beakers. Make sure that both beakers are
equally distant from the lamp and that both receive an equal amount
of light. Students should turn on the lamp and record temperatures
every minute for 10 minutes. Turn off the lamp and record the temperature
every minute for 10 minutes. Students should then graph their results.
(The soil will heat up faster and also cool off faster. The water
will warm up more slowly, but will then also cool off more slowly.)
Temperature map for this activity: http://www.comet.ucar.edu/dstreme/images/sfc_temp.gif
Simple explanation about why weather systems develop, due mainly
to the non-uniform heating of the Earth.
NOAA Office of Oceanic and Atmospheric Research web page for students
on ocean temperatures: includes good background information, activities
and links to additional resources.
More advanced explanation of sea and land breezes, and the relationship
to the uneven heating of land and oceans.
Return to: Creating an Earth System I
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