Air and Air Pressure

Mildred L.Butler               Douglass Math and Science Academy
                               543 N. Waller
                               Chicago IL 60644
                               (312) 534-6176
 
Objectives:

     To find air.
     To observe that air takes up space.
     To observe that air has weight.
     To observe that air exerts pressure.

Materials Needed:

  2 - 5 gallon clear aquariums   Equipment per group:
  water                          4-sticks
  soil                           2-balloons
  8-balloons                     1 container with a hole
  paper                          water
  clear glasses                  1 straw
  sticks                         1 pin
  cans with holes
  straws
  pins

Strategy:

     1.  Have the students take the piece of paper that is on their desk and fan 
         with it.  Discuss and have students draw conclusions.  Explain that air 
         is everywhere. 
     2.  Place a lump of soil in a container of water and have students observe. 
         Ask students did they see anything that might indicate the presence of 
         air in the soil?  Bubbles began to come out of the soil and go up to 
         the top of the water.  Discuss. 
     3.  Secure an aquarium or a container and fill it nearly full of water. 
         Turn one of the glasses upside down under the water. Ask students what 
         did they observe?  You will see that it stays full of air.  Put the 
         second glass under the water with the other hand.  Turn the second 
         glass on its side as you lower it so it fills with water.  Have 
         students make hypotheses.  Move the two glasses together and tilt the 
         first glass so that bubbles of air begin to rise into the second glass. 
         Have the students observe and draw conclusions: water in the second 
         glass is driven out by air rising from the first glass.  The first 
         glass fills with water, which replaces the lost air. 
     4.  Tie the end of one string tightly to the middle of a stick.  Hang the 
         stick up by the other end.  Slide the string along the stick until it 
         hangs exactly level.  Blow up one balloon and tie the neck with a 
         second string.  Blow up the second balloon until it is about the same 
         size as the first.  Tie a balloon on to each end of the stick.  Slide 
         the strings along the stick until the stick hangs exactly level again. 
         Now prick one balloon with a pin and watch.  Have students draw 
         conclusions: when you burst one balloon, all the air comes out.  The 
         other balloon with air in weighs more than the empty one, so the stick 
         goes down.  Now burst the other balloon and the stick will become level 
         again. 
     5.  Have students drink some liquid and explain how easily it comes up the 
         straw.  Then make a small hole in the straw about 2 inches (5 cm) from 
         the top end and try to drink again.  Ask students to explain why it 
         took much longer: when you suck through a straw, you lower the pushing 
         power of the air in your mouth and in the straw.  The air pushing down 
         on the surface of your drink forces liquid up the straw. 


References:

Schug, Ken. Demonstrations given during SMILE, Summer, 1993
Barbara Pawela, Ed Gudziol, Patricia Riley, Therese Donatello,
Resource books, 700 Science Experiments for Everyone, by Gerald
Wendth, Chemistry for Every Kid, by Janice Van Cleave, and
The Know How Book of Experiments.