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Wind: Classroom Activities

Air Pressure and Wind


Goal

To develop a better understanding of the relationship between air density, air pressure, and air flow.

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Background Information

Because air is a fluid, it can move easily from place to place. Although several forces affect the direction in which air moves, differences in air pressure are what set the air in motion. Wind is the movement of air from an area of higher pressure to an area of lower pressure. Most differences in air pressure are caused by the unequal heating of the atmosphere. When air over an area of Earth's surface is heated, it expands and becomes less dense. As the air becomes less dense, its air pressure decreases. If a nearby surface is not heated as much, the air above it will be cooler and denser. The cooler, denser air exerts greater pressure, so it flows underneath the warmer, less dense air, forcing it to rise. In this way, equilibrium is achieved as high-pressure areas relieve their pressure into low-pressure areas, producing wind.

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Activity Overview

Students run a model that looks at how differences in the temperature, density, and pressure of two parcels of air influence their movement. They observe how air, cooled by ice water below it, contracts. They infer that it increases in density and creates an area of high pressure. At the same time, they observe how air, heated by warm water below it, expands. They infer that it decreases in density and creates an area of low pressure. Using smoke from an incense stick to monitor air flow, they see how the warmer, less dense air moves upward and the neighboring colder and more dense air moves in to take its place.

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Materials and Equipment

clear flexible tubing (about 10cm long), ruler, matches, 2 x 1-L plastic bottles, incense stick, ice, hot water, cold water

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Activity

  1. Have students use a sharp knife or scissors to prepare the materials needed for this activity. Alternatively, because these preparations require the use of a sharp edge, you may want to do this yourself. First, have students cut a piece of clear tubing that is about 10 centimeters long. Next, have them cut a hole into the sides of 2 clear plastic bottles (1-liter). The holes should be 10 centimeters from the bottom and just large enough to fit the tubing.
  2. Have students connect the two bottles with the piece of tubing according to the following diagram:
    Bottle diagram
  3. Ask students to fill one bottle with cold water and ice and the other with hot water. The water level should be about 3 centimeters below the holes.
  4. Have them light an incense stick. After a few seconds they should blow it out. The stick should be producing a lot of smoke.
  5. Tell them to fill the bottle with cold water with smoke by holding the smoking incense stick inside the bottle for 10 to 15 seconds.
  6. Tell them to remove the incense stick and observe the movement of the smoke.
  7. Have students record and explain their observations.
    Air in the bottle with cold water becomes cooler, more dense, and sinks. The air above the hot water is warmed, becomes less dense, and rises. As the air moves upward, the neighboring colder, less dense air above the ice water moves in to take its place, carrying the smoke along with it.

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