The atmosphere is almost
invisible to the majority of people. Most young children do not even
realize that air is a “thing.” The atmosphere is very powerful especially
if you consider that weather is caused by the many interactions of temperature,
moisture, pressure, and wind. Ancient people had a difficult time
trying to figure out exactly what was in the atmosphere. In the fourth
grade, emphasis is on how the elements of temperature, pressure, and wind
When we discuss air pressure,
we don't usually realize that air presses on every side of an object.
Air exerts its force in all directions equally. Only in a vacuum,
where there is no air, is an object free from pressure.
Air pressure is real. In our
atmosphere air moves in part because of unequal heating of land and water
that creates air currents. The rotating Earth also causes movement.
The important concept to emphasize is that air is a real substance, that
interacts with the hydrosphere and land (lithosphere) to create different
Review with students that air is a substance that has
properties. Either do the demonstrations suggested below or have the students
perform them. The activities emphasize that air pressure is all around
us and we can use its “magic” if we understand it.
- Blow up a balloon and ask
students how to make the balloon fly. Hopefully the students will
realize that just releasing the unknotted tip will let the balloon propel
backwards. Why? The air is released and the force of the air
propels the balloon forward. [For every action, there is a reaction.]
- A simple experiment to illustrate
that air exerts a pressure is to place a balloon in an empty jar.
Blow into the balloon and inflate it in the jar. Notice that the
balloon will swell out until it touches the glass sides. A few more
puffs, and it becomes an easy matter to lift the jar with the air of the
The air pressure inside the balloon
exerts its force in all directions, pressing the walls of the balloon so
tightly against the glass jar that it cannot easily be pulled free unless
some air is released from the balloon.
- How can you make the little
ball in the Bernoulli pipe stay afloat? Blow into the pipe.
Just a stream of air increases the pressure below and makes the ball look
like it is floating. You have increased the air pressure below the
ball, which keeps the ball afloat.
- Can air be captured to help
machines fly? Yes, take for instance the puddle jumper. If
you curl the base away from your body and release it, notice that the puddle
jumper acts like a helicopter for a while. The design of the toy’s
wings helps to direct the air under the wood to help keep it afloat.