Air PressureAir Pressure

Air PressureAir PressureAir Air PressurePressure is is a measure of a measure of the force of the the force of the air pressing air pressing down on the down on the earth’s surfaceearth’s surface

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

Density = mass / Density = mass / volumevolume

Factors that affect Factors that affect Air PressureAir Pressure

TemperatureTemperature

Water Vapor

Elevation

DefinitionsDefinitionsDensityDensity = Mass / Volume. = Mass / Volume.

- Warm air is less dense than - Warm air is less dense than cool air.cool air.

- Moist air is less dense than dry - Moist air is less dense than dry air.air.

- Air at high altitudes is less - Air at high altitudes is less dense than air at lower altitudes. dense than air at lower altitudes.

TEMPERATURE AND AIR PRESSURE

HEAT

Molecules move faster

Move apart (less dense)

LESS AIR PRESSURE

HIGH TEMPERATURE, LOW AIR PRESSURE

LOW TEMPERATURE, HIGH AIR PRESSURE

AMOUNT OF WATER VAPOR

consists of air and water molecules

More water vapor means less air

molecules

LOW AIR PRESSURE

DRY AIR = HIGH AIR PRESSURE

(more dense)

Less dense

Where is air pressure higher, up in the mountains or

down in the valley?

http://www.youtube.com/watch?v=GWEyFbyvElc&feature=related

This bottle was photographed at 3600m (left) then again at sea level (right)

We all live underneath a huge ocean of air that is several miles deep: the atmosphere.

The pressure on our bodies is about the same as ten meters of sea water pressing down on us all the time.

At sea level, because air is compressible, the weight of all that air above us compresses the air around us, making it denser.

DensityDensity = Mass / Volume = Mass / Volume Warm air is less dense than Warm air is less dense than cool air. Warm air rises. Cool air cool air. Warm air rises. Cool air sinks.sinks.

Air at high altitudes is less Air at high altitudes is less

dense than air at lower altitudes.dense than air at lower altitudes.

Factors Affecting Air Factors Affecting Air PressurePressure

FACTORFACTOR Increase/ Increase/ DecreaseDecrease

DensitDensityy

Air PressureAir Pressure

TemperatuTemperaturere

warmerwarmer

Water Water VaporVapor

More More humidhumid

Altitude Altitude higherhigher

Measuring Measuring Air PressureAir Pressure

Air Pressure is measured by an instrument called Barometer

Types of BarometerMercury BarometerAneroidVIDEO: Why use mercury?

Air pressure increases, column of mercury rises

Air pressure decreases, column of mercury drops

Video (minute 2): http://www.youtube.com/watch?v=-gGBMCqBoSE&feature=related

Air PressureAir Pressure & & WeatherWeather

Weather map

Low pressure system: Increased cloudiness, winds, temperatures, and chance of precipitation.

High Pressure System: Indicates clear, calm conditions with reduced chance of precipitation. Drier air usually results in a greater range of high and low temperatures.

High pressure generally means fair weather

Air mass in upper atmosphere

Layer of Air

Warm, moist air cannot rise

No clouds

Low pressure generally means cloudy, rainy weather

Air masses move apart

Warm air rises, clouds form

QUESTIONS – use your QUESTIONS – use your knowledge of air pressure to knowledge of air pressure to explain the following explain the following situationssituations

A falling barometer is followed by A falling barometer is followed by several days of rainy weather.several days of rainy weather.

Some people find it hard to Some people find it hard to breathe at high altitudes.breathe at high altitudes.

A rising barometer indicates a A rising barometer indicates a spell of cool dry weather.spell of cool dry weather.

More QuestionsMore Questions

A series of hot, humid days is A series of hot, humid days is preceded by a falling barometer.preceded by a falling barometer.

A southern, coastal areas tend to A southern, coastal areas tend to have lower air pressure than an have lower air pressure than an inland area farther north.inland area farther north.

Rapidly dropping temperatures Rapidly dropping temperatures are accompanied by a rising are accompanied by a rising barometer.barometer.