Air pressure is difficult for children
to understand because it is difficult to see and feel. However, if air's
properties are made aware to children it is very easy for them to
understand. The atmosphere has its own weight or air pressure.
Air pressure is lower on the top of the mountains because there is less air to
weigh down from above. Cold air is heavier than warm air, which is
referred to as high air pressure. The warmer the air the lower the air
pressure. Air with a high moisture content is heavier than without moisture.
Galileo Galilei was the first person to
show air has weight and it was his student Evangelista Torricelli who invented
the barometer. He noticed that the level of mercury changes in a glass tube
open to air at the base.
- Show students the
“handboiler.” When you hold the bottom of the handboiler you will
notice that the liquid moves upward and looks like it is boiling.
However, what is happening is that you are increasing air pressure in the
vacuum. This causes the air to force the liquid (methyl alcohol)
up the tube, the “boiling” is actually the rest of the air.
- The air that is all around
us can act as a force. The following experiments illustrate air pressure
by doing several activities.
- Since this experiment requires water, it is
better to do experiments one at a time. Many of these activities
should be done over the sink, over a bucket or tray, or do it outside.
Tell students how long each exercise will take. On the students'
lab sheets, the exercises are illustrated. Use the outline below
to verbally review the instructions.
- Fill a plastic glass 3/4 full
- Place a piece of cardboard enough
to cover the top of the glass.
- Hold the card tightly on top
of the glass. Turn the glass upside down.
REASON: air pressure holds
the cardboard to the glass.
- Hold a small square piece of
paper against one end of a straw.
- Suck through the other end.
Release the paper.
REASON: air pressure holds
the paper against the straw
- Take the same straw and hold
your finger over one end.
- Push the other end straight down
into a glass of water.
- Now put straw in without finger
- After the straw is submerged
put finger on the top of straw and remove from glass.
REASON: air pressure prevents
water from going into the straw and once water is in straw it prevents
water from going out
- Using a large pan of water, put
a glass with a paper towel inside the glass and turn glass upside down
into the pan. The towel will not get wet.
- Put one glass filled with water
upside down, put another glass not filled with water next to the other
glass. Move the glass full of air so that an edge is under the glass
full of water, tipping it so that the air bubbles move up into the glass
full of water. Air will transfer from one glass to the other.
- You may want to refer to
Air is All Around Us by F. Branley, if you would like more information.