Download Air Pressure

Earth Science Rocks!
Bellringer—write the question
Question: Why does a hot air balloon rise?
Earth Science Rocks!
MYP Unit Question: What should I wear
today?
Area of Interaction: Environment
Learner Profile: Communicator
Earth Science Rocks!
Standard: Understand how the distribution
of land and oceans affect climate and
weather.
Learning Target: Today I am learning
about air pressure because it is a factor in
determining weather.
Air Pressure—Activating
Strategy
Create a 4 square
Air pressure notes
Egg in a bottle
Crushing cans with air pressure
What I learned today
Air facts
Air has mass.
Air takes up space.
Air has density.
Air pressure is the
weight of a column of
air pressing down on
an area.
Air Pressure
Air pressure is the
result of the column
of air that is above
you.
There is so much air
above you that at
sea level you have
14.7 lbs/in2 pushing
on you.
Pressure analogy
Imagine a stack of
books. The bottom
book feels all the
weight of the all the
books stacked above
it, while the second
one up feels slightly
less weight. The
higher in the stack,
the less pressure
one would feel.
Why are we not crushed by air
pressure?
Air pressure is equal
in all directions.
So air pushes equally
in all sides of us.
The forces are
balanced!
Altitude and Pressure
Altitude (or
elevation) is the
distance above sea
level.
The higher the
altitude, the less air
there is above you.
So as altitude
increases, air
pressure decreases.
Altitude and Density
As the air pressure
decreases, the density of
the air decreases. The
air particles are not
squashed together as
tightly the higher one
goes.
The air at sea level and
at 6km has the same 21%
oxygen, but at 6km there
are fewer molecules, so
you take in less oxygen
with each breath.
Air Pressure
As Air Pressure
decreases, so does
density.
Measuring Air Pressure
We use barometers to
measure air pressure.
Mercury barometer: a
glass tube sealed at the
top partially filled with
mercury.
Air pressure pushing on
the mercury in the dish
causes the mercury to
rise and fall in the tube.
Mercury Barometer
Aneroid Barometers
Aneroid Barometer:
Works without
liquid. Has an
airtight metal can
that is sensitive to
changes in air
pressure. This
chamber is
connected to a dial.
Units of Air Pressure
TV weather stations
and aviation use inches
of mercury.
Meteorologists (and the
NWS) use millibars, an
SI unit.
Flask Experiment & extra credit
Egg in a Bottle
Egg in
bottle
Fire heated air, causing it to expand and leave
the bottle.
When fire went out, temperature cooled,
molecules condensed, changing air pressure.
Since the pressure outside bottle was higher, the
higher pressure tried to get in the bottle.
Since the egg is squeezable, it got pushed into
the bottle by the air.
Crushing cans with Air Pressure
You explain it!
Hint: Air moves from high to low pressure.
Atmosphere