Chapter 5 – Chapter 5 – Earth’s WeatherEarth’s Weather

Lesson 1 –Lesson 1 –Earth’s AtmosphereEarth’s Atmosphere

What is air pressure?What is air pressure?

• Air is mostly nitrogen & Air is mostly nitrogen & oxygen.oxygen.• AtmosphereAtmosphere is the layers of is the layers of

gas (air) that surround Earth.gas (air) that surround Earth.• The atmosphere The atmosphere

consists of consists of fivefive layers. layers.• Weather happens Weather happens

in the lowest layer, in the lowest layer, the the tropospheretroposphere..

What is air pressure?What is air pressure?

• Air in the atmosphere Air in the atmosphere presses down onto Earth’s presses down onto Earth’s surface.surface.• air pressureair pressure: the amount of : the amount of

air pressing onto an areaair pressing onto an area• The The higherhigher you go, you go,

the the lowerlower the air the airpressure.pressure.

What can make air What can make air pressure change?pressure change?• Air pressure can be changed Air pressure can be changed

by:by:– amount of spaceamount of space (less space = more pressure) (less space = more pressure)– height above Earthheight above Earth (higher = less pressure) (higher = less pressure)– temperaturetemperature (warmer = less pressure) (warmer = less pressure)

What can make air What can make air pressure change?pressure change?• Air pressure can be changed Air pressure can be changed

by:by:– amount of water vapor, oramount of water vapor, or humidityhumidity (more humidity = less (more humidity = less pressure) pressure)

What is a barometer?What is a barometer?

• A A barometerbarometer is used to is used to measure air pressure.measure air pressure.

Mountain image courtesy of Mountain image courtesy of Wikimedia Commons and Wikimedia Commons and

used under a Creative used under a Creative Commons Attribution license. Commons Attribution license. All other images courtesy of All other images courtesy of

Microsoft Office Online.Microsoft Office Online.