Air Pressure

Ruthie L. Banks                Carter School
959 W. 71st Street             5740 South Michigan Ave.
Chicago IL 60621               Chicago IL 60637
(312) 723-0382                 (312) 535-0860

Objective:

 Students K-8 will be able to demonstrate the pushing power, or pressure, of
 air.

Materials Needed:

 Ice                           Cans (pop)
 Funnel                        Bowl
 Hot and Cool Water            Candle
 Graduated Cylinder            Index Card/Flat thin card
 Plastic Drink Bottle (soft)   Paper Cups 
 Clay                          Coin
 Glass Bottle                  Glass       
 Tissue Paper/Paper Towel

Strategy:

Ask students:  Did you know that air presses against you at all times?  Tell
them that they will see how air pushes, discover how air's pushing power,
or pressure, changes when you heat it, and find out what happens when you
reduce the air pressure inside a container.  Explain and demonstrate how air
takes up space.  Display the materials on the table and demonstrate the
following activities along with the students.

Activities:

1.  Paper Plunge:  Crumple a piece of paper and push it into the bottom of a
    glass.  Then plunge the glass straight down into the bowl of water.  Ask
    the students:
           1.  What happens to the paper?
           2.  Where is the water level in the glass?
    (Tell them) Water can only get into the glass by squashing/compressing the
    air inside it.  Air can be compressed, a little, but then it pushes back
    and prevents the water from reaching the paper.

2.  Cartesian Diver:  Have the students observe the eye dropper.  The
    eye dropper will rise and sink.

                (Ask them) Why the eye dropper rises and sink?

    Explain that when you put the dropper in the water, air becomes trapped 
    inside the dropper.  When you squeeze the bottle, water compresses the air 
    and the water takes up more space in the dropper, causing the dropper to 
    sink.  When you relax your grip on the bottle the air in the dropper top 
    expands again causing the water to be pushed out of the eye dropper. Then 
    the dropper floats back to the surface. 

3.  Jumping Coin:  First smear some cold water over the coin and over the top of 
    the bottle.  This will make an airtight seal when you rest the coin on top 
    of the bottle.  Hold your hands around the bottle and wait for about 30 
    seconds.  What happens to the coin?  Take your hands off the bottle and wait 
    again.  What happens to the coin now? 

4.  Sticking Together:  Cut a 1.5 cm hole in the middle of the blotting paper, 
    then wet it thoroughly.  Put a small amount of clay into the paper cup.   
    Stand a candle in the paper cup.  Tip the cup and light the candle.  Quickly 
    cover the cup with the wet blotting paper.  Then stand the second cup 
    upside-down on the top of the first cup, making sure that it fits exactly 
    over the first cup.  Wait until the flame goes out (about 20 seconds).  Then 
    lift the top cup gently.  If you have matched their rims exactly, the cups 
    should stick. 

5.  Crushing With Air:  Activity 1 (Bottle)
    Stand the bottle upright in a bowl.  Pour the hot water into it and leave it 
    for a short time.  Screw the top on the bottle.  Lay the bottle in the bowl 
    and pour ice cold water over it.  Then stand the bottle up. 
    
    Activity 2 (Can)
    Pour a small amount of water about (5 ml) into the can.  Heat gently over 
    candle.  When water begins to boil and steam rises from the can, remove from 
    the heat.  Quickly place the can upside down in the bowl of water.  
    (Answer)  The can/bottle retains it shape in a normal atmospheric condition, 
    because the air pressure inside the can/bottle is the same as the air 
    pressure outside.  The can/bottle collapse as the warm air inside the 
    can/bottle cools, it exerts less pressure.  The pressure of the air outside 
    is stronger and crushes the bottle/can.  (Ask students) 

           1.  What happened?
           2.  Which is stronger the pressure of the air outside
               or inside the bottle/can?
           3.  What made the bottle/can crush?
    

6.  Seal With Air:  Hold the glass over a bowl.  Carefully pour some water into 
    the glass.  Place the card on the glass.  Hold it down so the card touches 
    the rim all the way around.  Still holding the card, turn glass upside down.
    Let go of the card.  What happens?  (The water stays in the glass!) 

Performance Assessment:

After completing these activities students will be able to demonstrate various 
concepts about air; air exists, air has volume, air exerts pressure, hot air 
rises, and cold air has lower pressure than hot air.