Download Air Exerts Pressure

Air Exerts Pressure
Air molecules are constantly in motion, similar to a room full of bouncy balls
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With every bounce, air is exerting a force
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You do not feel the pressure of air at any one time because it is balanced on all times.
When air pushes from behind it is equally pushing in the front
Air Pressure is the force of molecules pushing on an area, air pressure moves in all
directions
Air Pressure Related to Altitude and Density:

Air pressure is determined by the weight (mass) of the air above it
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As you move up in the atmosphere you are also moving up in altitude, this upward
movement has less weight (mass) so there is less air pressure; less air pressure,
density and mass in Flagstaff.
If air pressure was the same in all places air would not move; air pressure is always
moving from areas of high pressure to areas of low pressure. Much like opening a can of
tennis balls or soda, there is little pressure inside, but the high pressure on the outside
rushes inward.
Barometers are instruments that measure the amount of air pressure. It is a flexible
machine that expands and contracts with the change in pressure
Movement of Air
Uneven heating of Earth’s surface causes air to move
Weather is the condition of Earths Atmosphere at a particular time and place.
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Wind is an important factor of weather
Wind is air that moves horizontally or parallel to the ground
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Much like air pressure, wind moves from areas of high pressure to low pressure
Formation of Wind:
1.
First, low pressure, or warm air, rises
2.
Second, high pressure, or cold air, sinks
3.
Winds then move across the surface of Earth
This can be such a slight change that you may not even feel the movement of the wind or
air
Some winds die after a short distance.
Global winds, however, travel long distances and may last weeks. Uneven heating between
the poles and the equator cause the winds
Coriolis Effect Curves the winds from the poles as the Earth rotates
Global Wind Belts
Doldrums are low pressure sections of air that do not move air quickly and are found at the equator.
Warm air is rising. The rising air in this area produces clouds and heavy rains
Horse Latitudes are high pressure sections of air that do not move quickly and are above and below
the equator. so cold air is sinking. Weather tends to be clear and dry in this area but can bring rain
across the United States
Wind Belts:
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Trade Winds blow from the east and move from the horse latitude to the equator
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Westerlies blow from the west and move from the horse latitudes to the poles. Bring storms across
the United States
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Easterlies blow from the east and move from the poles to mid-latitudes. Stormy weather occurs
when the easterlies cold air meets the warm air of the westerlies
Travel and Wind:
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The calm regions of the doldrums and horse latitudes make sailing difficult, boats may not move for
days or weeks, Wind belts are more ideal for sailing.
Jet Stream and Breezes
Jet Stream:
1.
Flow in the upper troposphere lower stratosphere
2.
Air moves at speeds greater then 200kilometers per hour
3.
Caused by uneven heating of Earths surface
4.
Two jet streams in each hemisphere; polar and subtropical
5.
Polar Jet streams affect weather in North America
6.
Jet Streams affect air travel because planes fly in this region. Depending on the strength of the
wind your plane ride may be shortened or lengthened
Local Breezes:

Winds change daily in a regular pattern
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As beaches heat up during the day the warm air rises and flows out to sea. Because the water takes
longer to heat up the water sends cool air to shore. This is why you would feel cool breezes while on
the beach

This same effect takes place in mountains and valleys. Mountains (beach) heat faster then valleys
(sea).
Monsoons
Monsoons are winds that change directions with the
seasons
- Caused by different heating and cooling rates
- Flow long distances and effect large areas
- Winter Monsoons occur when land is colder then the
sea
- Summer Monsoons occur when land is much hotter
then sea
Temperature Affects Water in the Air
1.
Water is always in the atmosphere
2. When temperatures change water changes form
3. Evaporation is changing from a liquid to a gas and condensation is a
gas changing into a liquid
4.
Gas in this process is water vapor
5. Precipitation is any liquid that falls to Earths surface
Humidity is the amount of water in the air
- Saturation of the air means that the amount of water evaporating is
equal to the amount of water that is condensing
Formation of Clouds
Clouds form when water vapor condenses
- Warm air
rises and cools as it gets higher, the cooling of
the air forms ices crystals or water droplets, these
droplets form the clouds
- The water must condense on to something hard, such as
the dust particles that are in the air. Smoke, and salt are
other examples
Fog: A cloud that rests on the ground or a body of water.
Has a smooth appearance. Forms when the ground is colder
then the air around it
Clouds
Cirrus:
A. Curl of Hair, form in high altitudes
B. Made of ice crystals, feathery appearance.
C. Winds form the tails of these clouds, these tails show the
direction of the wind in the upper troposphere. Seen in
fair weather, but can indicate that a storm is approaching
Clouds Continued
Cumulus:
•
Heap or Pile often like cotton balls.
Puffy white clouds, with dark bases.
• Form in the day time when warm air rises and the vapor condenses. If they
keep growing they produce showers.
• Smaller ones only produce light showers that last less then an hour, larger
ones that reach 18kilometers (11miles) will produce large thunderstorms
Stratus:
•
•
Spread-out, flat layers, appear gray.
Are smooth clouds because there is little wind when forming the clouds.
• If they are low they can produce light and steady precipitation as well as
block the sun and moon. When higher in the atmosphere they are thinner and
produce a halo of light around the sun and moon.
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