THE WEIGHT OF AIR

KEY CONCEPTS

  1. The atmosphere has weight and its entire weight exerts pressure on the earth's surface due to the influence of gravity. The Earth's air is estimated to weigh five billion tons, which translates to approximately fifteen pounds per square inch.
    • Click here to see an animation that depicts the thickness of Earth's atmosphere (710 K).
  2. The weight of air is known as atmospheric pressure or air pressure; its variations are caused by the circulation of hot and cold air.
 

MATERIALS

  • 2 balloons (equal size)
  • 2 strings, each 8 inches in length
  • ring stand
  • ring
  • dowel rod, 18 inches in length
  • (optional) QuickTime animation viewer installed on your computer
 
 

PROCEDURE

  
 
 

Activity

  1. Tie one string around each end of the dowel.
  2. Tie the deflated balloons to each string.
  3. Balance the dowel on the ring stand.
  4. Mark the balance point of the dowel with a pencil.
  5. Remove and inflate one balloon.
  6. Place the rod back on the ring stand in the original balanced position, according to the pencil mark.
  7. Discuss the results.
 
 

Assessment Ideas

  • Students should be assessed in lab procedure accuracy and interpretation of results.
  
 
 

CROSS-CURRICULAR IDEAS

  • Mathematics: Graph the results of the experiment.
  • English/Language Arts: Have the students keep journals and share results with their groups.
 
 

VOCABULARY

  • atmosphere: the mass of air that surrounds Earth.
  • atmospheric pressure: the weight of air exerting pressure on a unit area of Earth's surface
  
 

SOURCE

  • "Winds of Change" educational CD-ROM, Copyright Caltech and NASA/Jet Propulsion Laboratory