Chapter 1
The Atmosphere
Section 3
Air Pressure
Properties of Matter
• All matter in the universe has:
– Mass
– Volume
– Density
– Pressure
Is air matter?
How Do We Find Out If Air
Has Mass and Volume?
If you put that balloon filled
with air onto a triple beam
balance, would the mass
get bigger by the tiniest
amount or would it stay the
same?
It gets bigger…
THAT’S MASS!!!
As you breathe into a
balloon, does it grow or just
stay the same size?
It gets bigger…
THAT’S
VOLUME!!!
Properties of Air
• Because air has mass and volume, we can find
air’s density because
Density = mass/volume
Is Air Matter?
• Air has…
–Mass
–Volume
–Density
–Pressure
Put air in a balloon on a triple beam balance
Put air in a balloon and measure the size
Density = mass ÷ volume
Have you heard about “air pressure” before?
Properties of Air
• The force pushing on an area or surface is
known as pressure.
• Air pressure is the result of the weight of a
column of air pushing down on an area.
Properties of Air
Measuring Air Pressure
• A barometer is an instrument that is used to
measure changes in air pressure.
• There are two kinds of barometers: a mercury
barometer uses liquid, while an aneroid
barometer uses springs and levers.
Measuring Air Pressure
Increasing Altitude
• As you increase in
altitude (go higher
up), the air pressure
and air density
decrease because
the amount of air
above you gets less
and less and is more
thinly spread out