Learning target: _________________________________________________________________
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Chapter 15.2: Air Pressure
KEY TERMS
density – the amount of __________ in a given volume of air.
pressure – the force __________ on an area or surface.
air pressure – the result of a column of air __________ down on an area.
barometer – an instrument used to measure ____ __________.
altitude – the __________ above sea level (__________).
Properties of Air
 Because air has mass, it has other properties, including __________ and __________.
 __________ is the amount of mass in a given volume. You can calculate the density of a
substance by dividing its mass by its volume: density  mass
volume
Pressure
 There is a column of ____ above you all the time.
 The weight of the _____ is constantly __________
on your body.
Why doesn’t air pressure crush you?
 Molecules in air push in ALL directions – down,
up, sideways.
 The air pressing down on you is __________ by
the air pushing up on you.
 Air pressure can __________ from day to day.
 Denser air has _______ air pressure than less
dense air.
Measuring Air Pressure
 Two main types of barometers – mercury barometers and aneroid barometers
MERCURY BAROMETER
Air pressure pushes down on the surface of the
mercury in the dish, causing the mercury in the tube to
rise. The air pressure is greater on the barometer on
the right, so the mercury is higher in the tube.
ANEROID BAROMETER
This diagram shows an aneroid barometer. Changes in
air pressure cause the walls of the airtight metal
chamber to flex in and out. The needle on the dial
indicates the air pressure.
Altitude and the Properties of Air
Air Pressure and Altitude
 Air at sea level carries the weight of
all the air above it. As you go
higher, the air has less air on top of
it, therefore it weighs less. So, air
pressure __________ as altitude
increases.
Altitude and Density
 The density of air decreases as
altitude increases. Air at sea level
has more gas molecules in each
cubic meter than air at the top of a
mountain.
Use your notes above to answer the following questions:
1. Circle the letter of each sentence that is true about the properties of air
a. air has no density
b. air has mass
c. air that has more mass has greater density
2. True or False: Denser air has more air pressure than less dense air.
3. Match each term to its meaning:
density
a. The pressing down of weight on an area
pressure
b. the force pushing on an area or a surface
air pressure
c. the amount of mass in a certain volume
4. Circle the letter of each sentence that is true about barometers:
a. There are 2 kinds of barometers.
b. A barometer is used to measure temperature.
c. A barometer is used to measure air pressure.
5. Circle the letter of each sentence that is true about altitude
a. Altitude affects the density of air.
b. Altitude is the distance above sea level.
c. Altitude is also called elevation.