Air on the Go

In this activity, students will observe that air under high pressure will move toward an area of lower pressure.

Learning Objectives

  • Students learn that air moves from areas of higher presure to areas of lower pressure.

Materials

  • One clean/dry, clear 12-ounce plastic beverage bottle with cap off
  • One small, round wad of paper

Directions

  1. Hold the bottle approximately a hand’s distance from your mouth with the bottle flat on its side and the opening pointing directly at your mouth.
  2. Place the small round paper wad on the edge of the inside lip of the bottle opening.
  3. Ask students what they predict will happen to the wad of paper as you blow into the bottle. (Students may predict that the paper will move in the direction that you blow into the bottle.)
  4. Stand as still as possible and blow into the bottle. (Do not move your head or the bottle.)
  5. Ask students to observe what happens to the paper wad. By blowing into the bottle, you are increasing air pressure in the bottle. Air rushes out of the bottle toward lower pressure, pushing the paper out of the bottle instead of into it.
  6. Repeat the demonstration several times so that students understand whether it happens in the same way each time.

Ask students the following questions

  1. What pushed the paper out of the bottle? (Air!)
  2. Why was air moving out of the bottle? (Because more air had been pushed into the bottle.)
  3. An area where air is pushed together is an area of high air pressure. Where is the air pressure highest in this demonstration: inside the bottle or outside the bottle? Where is air pressure lowest? (Air pressure is higher inside the bottle than outside the bottle.)
  4. How does air move when there are differences in air pressure? (It moves from high pressure to low pressure.)
  5. What would happen to the paper if there was a hole in the bottom of the bottle? (Pressure wouldn't get as high inside the bottle. Try this and other ideas that students have based on this activity.

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Background

Although air is invisible, it still takes up space and is made of molecules. There is more space between the air molecules in a room than the air molecules in a balloon, for example. Under high pressure, air molecules are more densely packed. Under low pressure, air molecules are less densely packed. When you blow into the bottle in this activity, air is compressed and air pressure inside the bottle increases.

Air moves from areas of high pressure to areas of lower pressure as the air molecules attempt to spread out. For example, if you let go of a balloon that you have blown up but not tied, the air rapidly exits. The air is moving out of the balloon to an area of lower pressure. The greater the difference in pressure, the faster the air will move. The air blown into a bottle is a lot like air blown into a balloon. If it’s not trapped, it will rush out of the bottle toward lower pressure. Consequently, the paper is pushed out of the bottle instead of into it.

In the atmosphere, air moves toward low pressure and its motion is also influenced by the spin of the Earth. This is called the Coriolis Effect and causes air to move counterclockwise around low pressure in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Air pressure records:

  • United States
    • Highest: 31.85 inHg (1078.8 mb) in Northway, Alaska, on January 31, 1989
    • Lowest: 25.10 inHg (850 mb) in Manchester, South Dakota, on June 24, 2003 during an F4 tornado
  • Global
    • Highest: 32.06 inHg (1084.8 mb)in Tonsontsengel, Mongolia, on December 19, 2001
    • Lowest: 25.69 inHg (870 mb) in the Philippine Sea in the southwestern Pacific Ocean during Typhoon Tip on October 12, 1979