Water Cycle - Atmosphere (3)
Lab 

   
OBJECTIVES:
  • Exploring atmospheric pressure.
  • Experimenting with bubbles and atmospheric pressure.
VOCABULARY:
  • atmospheric pressure
MATERIALS:

Students experiment with bubbles.

BACKGROUND:

Atmospheric pressure refers to the weight of the air exerting a force or pressure on an object.  All things, living and non-living, are subjected to this pressure.  Students do not usually think of themselves as being on the surface of the Earth with tons and tons of air on them.  They assume that they could not possibly be able to walk around with such pressures placed upon them. 

An instrument called a barometer measures the atmospheric pressure. An analog to a barometer is a handboiler or love meter.  Let one of the students hold the meter in their hand.  The class should observe what happens and try to figure out what causes the liquid to boil.  Many will assume that the heat of the hand boils the liquid,  but it doesn't.  The liquid inside the glass chamber is usually methyl alcohol or another liquid that has a low vaporization rate.  The heat of the hand starts to vaporize the liquid, that in turn changes the pressure inside the chamber and forces the liquid up.  The air in the chamber then is forced up after the liquid is up and it appears like it is boiling.

Air has weight and hence creates pressure.  The weight pulls down on us and creates a pressure.  The pressure is equal in all directions.  In this activity the students will use different bubble makers to discover that the reason bubbles are spheres, is because the pressure acts on their surface equally, forming a sphere. In space where is there is not air pressure, the pressure is still equal so you will still get spherical bubbles. 

PROCEDURE:

  1. Use the Tour of Bubbles to watch the bubbles move upward.  Notice at the beginning of the bubble, they are more oblate (flattened). As the bubble moves upward it becomes spherical.  This is because the pressure is equal when it is spherical and unequal when it is oblate. 
      
  2. Use the bubble trumpet or other bubble makers to have children look at the shape of the bubbles that leave the trumpet.  
      
  3. Give groups of students 4 pieces of stiff wire (no more than 10 cm long).  Direct them to make a shape of  a circle, triangle, and square.  The fourth shape can be one of their choice.
      
  4.  Students should do 4 trials of each wand and record their information.  Scientific experiments always need more than one experiment to prove something.  All the bubbles should be spherical.
      
  5. Students should test their bubble makers using bubble solution.  Below are some solutions that you can use.  Note: Dawn (or other soap with high glycerine content) can be substituted for glycerine.

 BUBBLE MAKERS

An instrument that makes bubbles can be just about any size.  The smaller the bubble maker the thinner the wire can be.  If you are making a large bubble maker stiff wire (like a clothes hanger) is required.  If you are using a clothes hanger, you might have to wrap twine around the wire to help the solution adhere to the wire.  Clothes hangers usually have a coating on it that makes it hard for the solution to adhere.   Dip  your bubble makers into the soap mixture and blow through it very gently.  The skin will stretch and eventually a bubble will break free. A twist in the wrist will insure that the bubble will go free. 

MATERIALS:  clothes hanger or other stiff wire, twine


SIMPLE SOLUTIONS:

  1. Mix 1 part soap to 1 part glycerine to 6 parts distilled water
  2. Put 3 or 4 tablespoons of soap powder or soap flakes into four cups of hot water.  Let the mixture stand for 3 days and then stir in a large spoonful of sugar
     

OTHER SOLUTIONS THAT YOU MAY WANT TO TRY:

  • 3 parts water, 1 part Karo Syrup, 1 part glycerine, 2ml salt. 
        
  • 3 parts water, 1 part detergent, 1 part glycerine, 2 ml salt 

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