Air Pressure
• I can compare and contrast high and low
pressure systems.
• I can describe that high pressure systems
result in fair weather due to air sinking,
and low pressure systems may result in
severe weather due to air rising.
Air Pressure
Air Pressure
• Air Pressure is
a measure of the
force of the air
pressing down on
the earth’s surface
Air Pressure can vary at any
particular point on the Earth
depending on the density of the air
Density = mass / volume
Density of Air
Density = Mass / Volume
 Warm air is less dense than
cool air. Warm air rises. Cool air
sinks.
 Air at high altitudes is less
dense than air at lower altitudes.
Measuring Air Pressure
Types of Barometer
Air Pressure
is measured by
an instrument
called A
Barometer
Mercury Barometer
Aneroid
Air Pressure & Weather
Low pressure generally
means cloudy, rainy
weather
Air masses
move apart
Warm air
rises, clouds
form
High pressure generally
means fair weather
Air mass in upper
atmosphere is
sinking (cold, No
dense air)
Layer of Air
clouds
Warm,
moist air
cannot rise
Weather Map Symbols
Fronts
•I can describe the causes and
effects (weather conditions) of
cold fronts, warm fronts, and
stationary fronts.
What are Fronts?
• Fronts happen when
2 different air
masses meet BUT
they do not mix
together
•4 Different Types of Fronts:
• Cold Front
• Warm Front
• Occluded Front
• Stationary Front
Fronts: Mr Parr Rap Song
How do air masses move?
• Cold air (more dense)
ALWAYS sinks under warm
air (less dense).
• So what is the difference
between the 4 types of fronts?
– Which air mass takes over
the other! It’s a
battleground.
– One air mass is pushing
the other out of the way
because it does not want
to mix!
Video on Air Masses:
http://www.youtube.com/watch?v=vPC5i6w3yDI&f
eature=related
Demos:
• http://www.classzone.com/books/earth_sci
ence/terc/content/visualizations/es2002/es
2002page01.cfm?chapter_no=visualization
Hot and Cold Water Demo:
http://www.youtube.com/watch?v=Ak9CBB1bTcc&feature=related
Cold Fronts
What happens? A fast
moving cold air mass
runs into a slow moving
warm air mass, pushing
the warm air up
quickly to form clouds.
Weather forecast:
heavy rains and
thunderstorms
Cold Front: Weather map symbol
• A cold front symbol—The direction that
the teeth point indicate the direction the
front is moving.
Warm Fronts
What happens? A
fast moving warm air
mass collides with a
slowly moving cold
air mass. Warm air
slowly moves over the
cold air.
Weather forecast:
slow steady rain!
Warm front: Weather Map Symbol
• Warm Front symbol—The directions that
the bumps face is the direction the front is
moving.
What types of fronts can you find on
the map? In which direction are they
moving?
Stationary Front
 What happens: A cold air
mass and warm air mass
meet, but neither air mass
has enough force to move
the other air mass.
 Can sometimes mix
together OR will turn into
a warm or cold front.
 Weather forecast: clouds,
rain for multiple days
Stationary Front: Weather Map Symbol
Not moving in
any direction!
What types of fronts can you find on
the map? In which direction are they
moving?
Summary of Front Symbols
Practice Reading Weather Maps
Which types of fronts can you find on this
map?
What types of fronts are on the map?
In which direction are they moving?
What type of weather would it produce?
What types of fronts are on the map?
In which direction are they moving?
What type of weather would it produce?
What types of fronts are on the map?
In which direction are they moving?
What type of weather would it produce?
Analyze a Map
Front Classification
• 1. When a warm air mass moves in on a cold air mass.
• 2. When a warm and cold air mass meet, but neither one
has enough force to rise over the other.
• 3. Brings gentle rains that may last for hours or days.
• 4. Strong winds are formed followed by heavy rain,
crashing thunder, and flashing lightning.
• 5. When the front passes, the temperature warms up and
it becomes humid.
• 6. When the front passes, the weather turns cooler.
• 7. Tornados could occur.
• 8. Usually happens and is over with quickly.
• 9. Stay in the same area for a long period of time.
• 10. When a cold air mass moves in on a warm air mass.
11. Causes warm air to move up slowly
• 12. Causes warm air to move up quickly
Interpreting Weather Maps
• In groups, complete the interpreting
weather maps activity
• When finished, work on the “Reading a
Weather Map” Worksheet
Inverted Cup
cardboard
Air Pressure
When cup is completely
filled with water, no air is
left in cup, thus no air
pressure. The inverted
cup can therefore hold
water up because the air
pressure is working
against the underside of
the cup.
There is higher air pressure outside pushing
upward than the inside of cup pushing downward.
Collapsing Can
Before heating, the can was filled with water and air.
By boiling the water, the liquid changed into water vapor
 The water vapor or steam pushed the air that was inside, out of the can.
 In closing off the can, air is prevented from going back to the can.
 Cooling (water in basin) condenses water vapor back to water. All the
vapor which took up space inside the can turned into a few drops of
water, which take up less space.
 Pressure inside can drops allowing outside air pressure to push on the can and
crush it.
Straw Drinking Race
The higher pressure in
outside air pushes the
liquid up the straw in our
mouth
Sucking creates a
partial vacuum or a
lower pressure in
straw above the
liquid that we drink
The student with the
leaky straw cannot
create a vacuum above
the liquid, so the liquid
is not pushed up.