Name:_______________________________________
AIR PRESSURE homework
Hold the eraser of a pencil against the palm of your hand. Now press down. What you
feel is the force of the pencil pressing against your hand. You feel pressure. As we know,
the air in the atmosphere is made up of a number of gases. These gases press down on the
Earth’s surface, exerting a force that we call atmospheric pressure or air pressure. Although
we are usually unaware of this pressure, it actually presses down very hard – roughly
equivalent to the force of an elephant balancing on a desk! The air pressure at any point on
the Earth is equal to the weight of the air directly above that point. We are walking on the
bottom of an “ocean” of air about 800 kilometers deep!
Air pressure can vary from one point to another on the Earth’s surface. The air
pressure at any particular point on the Earth depends on the density of the air (density
is equal to mass divided by volume.) Denser air has more mass per unit volume than less
dense air. So, denser air exerts more air pressure against the Earth’s surface than less dense
air does.
FACTORS THAT AFFECT AIR PRESSURE
The density of the Earth’s atmosphere, and thus air pressure, is affected by 3 factors:
temperature, water vapor, and elevation. As you have learned, the density of a fluid
decreases when the fluid is heated. Less dense air exerts less air pressure. So places with
high temperatures usually have lower air pressure than places with low temperatures.
At a given pressure, moist air is less dense than dry air. This is because a water
molecule has less mass than either a nitrogen or an oxygen molecule. Thus air with a large
amount of water vapor in it exerts less air pressure than drier air pressure than drier air.
AIR PRESSURE AND WEATHER
Because air pressure changes with changes in temperature and elevation, air pressure
can be measured with and instrument called a barometer. Barometers can be used to help
forecast the weather. Air pressure may become relatively high when large masses of air
come together in the upper atmosphere. These air masses press down on the layers of air
below. This pressure usually prevents warm, moist air from rising into the upper atmosphere.
As a result, clouds do not form. So high pressure usually means fair weather. But there are
exceptions.
Air pressure may become relatively low when large air masses move apart in the upper
atmosphere. This reduces pressure on the layers of warm air below. As a result, the warm
air rises. If the warm air is moist clouds will form in the upper atmosphere. So low pressure
can lead to cloudy, rainy weather.
Name:_______________________________________
Air pressure HOMEWORK SHEET QUESTIONS
1.) What is air pressure?
2.) What is the relationship between the density of air and air pressure?
3.) List and describe 3 factors that affect air pressure.
4.) How is air pressure measured?
5.) Which of the following cities has the highest air pressure? Which
one has the lowest? Explain
a. Atlanta, Georgia: elevation 320meters
b. Boise, Idaho: elevation 825 meters
c. Denver, Colorado: elevation 1600 meters
d. Salt Lake City, Utah: elevation 1300 meters