The direction of air movement, is in part,
controlled by air pressure. Warmer areas tend to have a low pressure (warmer
air is less dense, molecules are farther apart, hence low pressure) and cooler
areas tend to have high pressure (cooler are more dense or compact).
High pressure is usually associated with
dry weather because as air sinks and warms, water in the air will evaporated.
Low pressure is usually associated with moist weather because as air rises and
cools, water vapor tends to condense.
Under the same solar radiation
(temperature), different substances will heat up differently. Oceans heat up
slowly, but cool very slowly. Land heats up quickly, but then cools quickly.
This causes a difference in air pressure which in turn causes wind. Breezes
can be caused by conditions created by this changing heat.
Air that is warmed exerts less pressure on
the ground causing a low pressure region. Air that is cooled is denser,
causing a high pressure region. Remember that cold, cool, warm, and hot are
relative terms. The movement of air is greatest from high pressure to low
pressure when the temperature differential is the greatest.
The lab exercise is to prove
to students that certain substances will heat up more quickly than others.
In your discussion you might want to review that heat makes molecules
of a substance move faster.
Emphasize with students that wind
is caused in part, when there is an unbalance in the heating of the earth.
They should conclude that water takes longer to heat up, and also longer
to cool down. Light sand reflects more heat than dark sand, so it
takes longer to heat up. Salt water takes more heat to warm up than
fresh water. Review that the different surfaces on earth (water,
ice, soil, and rock) heat at different rates and cause different air pressures.
Heat lamps work quickly in the classroom.
If you are using sunlight this activity may require more time.
- Put the materials listed
in the student’s lab sheet in a tray or cup. You can easily substitute
or add objects. Make sure there is enough material so the thermometer’s
reading is accurate.
- Place a thermometer into
each of the materials listed. Emphasize with students that
each thermometer is the same distance below the surface.
- Students should record the
starting temperature of each of the materials in students data table.
- Students should place their
tray in the sunlight (heat lamp) for 10 minutes and record the temperature
in their data table.
- Bring the trays inside (or
turn off the heat lamp) and let them cool for 10 minutes before students
record the temperatures.