Air Pressure

Brian Cagle                    John W. Cook
                               8150 S. Bishop
                               Chicago IL 60620
                               (312) 535-3315

Objective: 

    The main objective of the mini-teach is to demonstrate an understanding of 
how air pressure works.  Students will be able to identify, construct, and      
define the concept of air pressure by working in groups after experimenting 
with various activities on air pressure.  Students will also have a working 
knowledge of the different terminology used when describing the process of air 
pressure. 

                                 Activity #1: Water Fountain
    
Materials: 

    2 jars (one with the lid), 4 straws, small bucket, water, tape              

Strategy:  

    Make two holes in the jar lid, one hole in the middle of the lid and the 
other near the edge.  Place one straw in the middle hole and secure both ends  
of the hole with clay.  Now tape the three straws together and place one end    
inside the second hole of the jar lid about an inch.  Secure both ends of this 
hole with clay.  Fill jar #1 without the lid about three-fourths of the way  
with water.  Now fill jar #2 with the lid about 2 inches high with water and 
then close the lid.  Take jar #2 with the lid and turn it over so that the 
one straw in the middle hole is half-way in jar #1 and half-way in jar #2.
While the other straws which are connected are hanging over the edge into a   
small bucket.  Now observe what happens in jar #1 and jar #2. 

Results:

    As the water from the closed lid jar #2 pours down into the small bucket    
through the connected straws, the air pressure inside the jar become less as 
the air spreads out to take up space left by the water.  The air outside in     
jar #1 is at a greater pressure than the air inside, thus forcing the water up 
the straw and making a fountain. 

                                 Activity #2: The Magic Glass

Materials:

    Jar, 4"x6" index card, water

Strategy:

    Fill the jar to the top with water and wet the rim slightly.  Lay the card 
on the top of the jar.  Hold the card firmly in place and turn the jar over.  
Now take away your hand and see what happens. 
    
Results:

    The water should stay in the glass, showing that air pressure is exerted on 
the card from the top, the side, and the bottom as Pascal's law states.

                                 Activity #3: Candle In Glass

Materials:

    Shallow dish or pan, candle, matches, tall glass or flask, food coloring

Strategy:

    Light a candle and stand it upright in the middle of a pan and secure it 
with melted candle drippings.  Fill the pan half full with water.  Then add a  
drop of food coloring to the water to make it more noticeable from the back of 
the room.  While the candle is still burning, place a narrow glass or flask 
over the candle.  Carefully observe the base of the container, the water level 
in the container, and the flame.  Record your observations.

Results:

    The candle will burn for a time but will eventually go out and you will see 
that the water rises up into the jar.  You will find out that the water will 
rise about one-fifth of the way up the jar.  Water rises in the container due 
to an imbalance in pressure.  As the gas inside the container heats and expands 
causing bubbling around the base.  The oxygen inside diminishes, the flame gets 
cooler, and so does the air resulting in a pressure drop.  Water starts to move 
into the container.  When the candle is extinguished, the temperature in the 
flask drops, causing a further reduction in pressure and a further rise in the 
water level.  

                                 Activity #4: The Power of Air

Materials:

    Ruler,  2 sheets of notebook paper, 2 sheets of newspaper 

Strategy:

    Lay the ruler on the table so about one-third of it lies over the edge.
Place two sheets of notebook paper on the ruler and press against the table 
until the paper is flat as possible.  Now hit the overhanging portion of the 
ruler with your hand and try to make the paper fly into the air.  Repeat this 
procedure using two sheets of unfolded newspaper and record your results.
 
Results:

    The ruler should snap when placed under the newspaper, but not when placed  
under the notebook paper.  The notebook paper is small enough that the ruler    
can lift it without breaking.  While the newspaper has a much greater surface 
area than the notebook paper.  The air presses down on the sheet of newspaper,  
there is a lot of air pushing down on it and this is enough to stop the paper 
and ruler from moving.


Performance Assessments: 

    Through an oral evaluation and teacher observations each student will have 
to describe the procedure of each activity and the results of each experiment. 
Explaining what happens when their is an indifference in air pressure and what  
caused it.

Conclusion:

    After experimenting with each activity, each student should have an 
excellent idea of how air pressure works.  While having a working knowledge 
of some of the key terms associated with air pressure such as: high air 
pressure, difference in pressure, and low air pressure.