Properties of Air
Mass
 Air has _________.
 Why?
Atoms
 Air is made up of ___________
Molecules
+ ___________.
Density
 Mass ÷ Volume = __________
increases as the # of
– Density ____________
molecules in given volume increases.
decreases as the # of
– Density ____________
molecules in given volume decreases.
** Volume = amount of space matter takes
up!
** Remember: atoms/molecules make up
matter.
Warm Air vs. Cold Air
1
2
Which of the two above represents cold air?
Why?
Which of the two above represents warm air?
Why?
Warm Air vs. Cold Air
1
2
Warm air because it has _______
less
# 1 = __________
molecules.
Cold air because it has _______
# 2 = __________
more
molecules.
Warm Air vs. Cold Air
 Why do hot air balloons rise?
– Air is heated. Molecules bounce off each other. As a
result, there are less molecules in a given volume. The
warm air in the balloon is less dense than the cold air
around the balloon so the balloon rises!
Air Pressure
 What is pressure?
– Force pushing on an area.
– Denser air exerts __________
more pressure
because _________________________
there are more molecules
in a given volume.
– As altitude increases, air pressure
decreases
__________________.
Temperature at Altitude
Sea Level
10,000 Feet High (on
top of mountain)
colder at the top of a mountain because
 It is __________
the molecules are not bumping into each other as
much.
 Cold air ________
sinks and warm air ________.
rises
 When warm air rises, the molecules spread out &
then the air becomes colder. This cooled air sinks.
Air Pressure Continued
 The amount of air pressure being exerted
on your desk and you is the weight of a
school bus. Why are you not smashed like
a pancake?
– Air pressure acts in ALL directions.
Overview: Properties of Air
 Properties of Air
– Mass
– Density
– Air Pressure