Transcript Air Pressure - Laconia School District

Air Pressure
Ch 15 Sec. 3
By:Irma Krupic
T-3
Contents
Guide for reading
 Properties of air
 Measuring air pressure

Properties of Air
Atoms,mass,molecules,
density,pressure.
 Density:amount of mass
in a given volume of air.
 The more molecules in
a given volume of air
the higher the
density.Fewer molecules
=low density.
 Force pushing on an
area is pressure.



Denser
substance=more mass
per unit volume than a
less dense one.
Air pressure: weight of
a column of air pushing
down on an
area.Molecules in air
push in all directions.
Instrument Used to Measure
Air Pressure
Mercury
barometers+aneroid
barometers are
used to measure changes
in air pressure.
 Falling air
pressure=storm is
coming.
 Rising air
pressure=weather is
clearing.

Mercury Barometer
Was the first barometer invented.
 Glass tube open at bottom. Partially filled
with mercury. Space above the mercury has
no air.Open end of tube is in a dish of
mercury.Air pressure pushing down on
surface of mercury in dish is equal to weight
of column in the tube. When air pressure
increases ,it presses down more on the
mercury. Greater air pressure makes the
column of mercury higher.

Aneroid Barometer
Has airtight metal
chamber,metal chamber
is sensitive to changes
in air pressure.
 As air pressure
increases,thin walls of
chamber push in. As
pressure drops,walls
come out.
 Chamber is connected
to dial be series of
springs +levers.When
shape of chamber
changes needle on dial

Units of Air Pressure




Inches of mercury.
National weather
service maps use
millibars to measure air
pressure.
One inch of mercury
=33.87 millibars.
30 inches of
mercury=1016
millibars.
Increasing Altitude
Air pressure at the top of mount
McKinley is more than 6 kilometers
above sea level, that’s less than half the
air pressure above sea level.
 Altitude-distance above sea level.Air
pressure decreases as altitude
increases. When air pressure
decreases,so does density.

Altitude Affects Density



Air pressure is greatest
at sea level.
Near the top of the
atmosphere it has less
weight pressing on it.
As you go up through
the atmosphere, air
pressure decreases, and
as air pressure
decreases,the density of
air decreases too.
Web Resources
http://www.grc.nasa.gov/WWW/K12/airplane/pressure.html
 http://kids.earth.nasa.gov/archive/air_p
ressure/
