Air Pressure

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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.

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Air Pressure
3
Air Pressure

• Air Pressure is a measure of the force of the air
  pressing down on the earths surface

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Air Pressure can vary at any particular point
on the Earth depending on the density of the air

• Density mass / volume

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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.

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Measuring Air Pressure
Types of Barometer
Air Pressure is measured by an instrument called
A Barometer

• Mercury Barometer

• Aneroid

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Air Pressure Weather
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Low pressure generally means cloudy, rainy
weather
Warm air rises, clouds form
Air masses move apart
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High pressure generally means fair weather
Air mass in upper atmosphere is sinking (cold,
dense air)
No clouds
Warm, moist air cannot rise
Layer of Air
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Weather Map Symbols
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Fronts

• I can describe the causes and effects (weather
  conditions) of cold fronts, warm fronts, and
  stationary fronts.

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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
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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! Its 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
?vvPC5i6w3yDIfeaturerelated
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Demos

• http//www.classzone.com/books/earth_science/terc/
  content/visualizations/es2002/es2002page01.cfm?cha
  pter_novisualization

Hot and Cold Water Demo http//www.youtube.com/wa
tch?vAk9CBB1bTccfeaturerelated
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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

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Cold Front Weather map symbol

• A cold front symbolThe direction that the teeth
  point indicate the direction the front is moving.

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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!

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Warm front Weather Map Symbol

• Warm Front symbolThe directions that the bumps
  face is the direction the front is moving.

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What types of fronts can you find on the map? In
which direction are they moving?
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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

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Stationary Front Weather Map Symbol
Not moving in any direction!
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What types of fronts can you find on the map? In
which direction are they moving?
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Summary of Front Symbols
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Practice Reading Weather MapsWhich types of
fronts can you find on this map?
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What types of fronts are on the map? In which
direction are they moving?What type of weather
would it produce?
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What types of fronts are on the map? In which
direction are they moving?What type of weather
would it produce?
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What types of fronts are on the map? In which
direction are they moving?What type of weather
would it produce?
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Analyze a Map
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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

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Interpreting Weather Maps

• In groups, complete the interpreting weather maps
  activity
• When finished, work on the Reading a Weather
  Map Worksheet

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Inverted Cup
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.
cardboard
Air Pressure
There is higher air pressure outside pushing
upward than the inside of cup pushing downward.
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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.
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Straw Drinking Race
The higher pressure in outside air pushes the
liquid up the straw in our mouth
The student with the leaky straw cannot create a
vacuum above the liquid, so the liquid is not
pushed up.
Sucking creates a partial vacuum or a lower
pressure in straw above the liquid that we drink