Air is a mixture of gases that has weight, takes up space, and can be compressed. It exerts pressure in all directions that increases with temperature as the gas particles move faster, and decreases with altitude as there is less air above pressing down. Experiments like the upside-down cup, balloon, and Cartesian diver demonstrate these key properties of air.

2. Properties of air
 Air is an example of matter. Air is a mixture of gases
consisting of approximately 4/5 Nitrogen and 1/5
Oxygen. Like all matter, air has weight and takes up
space. It can also be compressed, unlike solids and
liquids. These three properties will be studied in this
investigation.
 Air has weight--Weighing Air
 Air takes up space--The Upside-Down Cup
 Air can be compressed--The Cartesian Diver
Air Takes Up Space

3. Air Exerts Pressure

 Take a meter stick and lay it on a table. Unfold a full page of a
newspaper and lay it flat over the meter stick. Push down on the other
end of the meter stick. What happens? Why can’t you lift a super-light
piece of paper? Air exerts pressure (in all directions).
 The air above the paper pushes down on it (pressure). This pressure is
what makes the paper lay flat on the table - it’s being pushed down.
Even though they’re too tiny to see, all the molecules of air in the
atmosphere above your head weigh something. And the combined
weight of these molecules causes a pressure pressing down on your
body of 10,000 kg per square meter (10,000 kg = 22,000 lbs). This
means that the mass of the air above the 0.1 square meter cross section
of your body is 1,000 kg, or a tone.

4. Air is affected by Temperature

 Take a balloon and place it over the top of a pop bottle
(2L is best with a little bit of water in it). Observe the
size of the balloon now (@room temperature). Now
place it in a freezer for 10 minutes, remove it and
observe size of balloon. Now take the bottle and hold
it in a baking dish of almost-boiling water for 10
minutes. Now let the bottle sit on the table for 10
minutes. You should now see the balloon return to the
same size as it was to start.

5. Air is affected by Temperature
 The greater the temperature, the faster the air particles
move (increasing pressure), hitting the sides of the
balloon more often and harder, making the balloon
inflate more. The colder the air becomes though, the
slower the air particles move (lowering pressure),
resulting in the same amount of air now taking up less
space. This is why the beach-ball you left in the garage
over night will be “smaller” in the morning that it was
during the day (when it was warmer)

6. Air has weight
 Air has weight. Matter has three forms which are solid,
liquid and gas. Air is a mixture of gases so it will have
weight. We can demonstrate that air has weight by
comparing a full balloon with an empty balloon

7. Air takes up space
 The Upside-Down Cup demonstrates that air takes up
space. Students are challenged to devise a way to
submerge a tissue in water in such a way as it does not
get wet. The solution is to stuff the tissue into the
bottom of a cup which is then held in the water
upside-down.

8. Air Takes Up Space
 Take an empty Ziploc bag, open it and pull it through the air like
a parachute. Now close it, seal it and try to squish the bag.
There’s nothing in the bag, right? Wrong. The ziploc bag is full
of air.

 You can also prove this by blowing up a balloon. The balloon
expands because you are putting something into the balloon; air.
This air takes up space, so the more air you put into the balloon,
the more space it takes up. When you use a pump to blow up a
football, you don’t put nothing into it, you put air into it - this air
takes up space which is why the football expands.

9. Air can be compressed
 The Cartesian Diver demonstrates that air can be
compressed. It is generally credited to Rene Descartes,
the French mathematician and scientist who also
developed the Cartesian Coordinate System which we
use for making graphs.

10.  Despite this “pretend” atmosphere, the air pressure
inside an plane is not the same as at sea level. You
might have noticed that if you drink from a plastic
bottle during a flight and put the lid back on, when
you land the bottle will be crushed. This is because the
air in the bottle is at the lower pressure of the airplane
cabin and it can’t withstand the higher air pressure at
ground level.
Air is affected by Altitude

11. Air is affected by Altitude
The higher you are, the lower the air pressure. There is
less air above you to push the air down (which would
increase the air pressure). This is why climbers on
Everest use oxygen tanks - the air outside is too thin at
the summit for them to breathe normally. Human
bodies are used to air pressure. The air pressure in our
lungs, ears and stomachs is the same as the air
pressure outside of our bodies, which ensures that we
don’t get crushed. Our bodies are also flexible enough
to cope when the inside and outside pressures aren’t
exactly the same. Airplanes need pressurized cabins to
compensate for the lower air pressure at high altitudes