Chapter 11 Section 5 Notes
What is air pressure?
Name: ______________________________________
Date: ________________________
Weight and Pressure
❖ Weight is a _______________.
➢ If you hold a book in the palm of your hand, you feel the _______________ of
the book _______________ down.
➢ This force is measured in units called _______________ (N).
➢ A 1-kg mass has a force of about 10 N.
❖ The _______________ of force per unit of area is called _______________.
➢ When you hold the book in the palm of your hand, the book’s weight is
_______________ over your hand.
➢ Suppose the book’s force is 10 N, and your hand has an area of 110 square cm,
or 100 cm​2​.
➢ The force on each square centimeter is then 10 N divided by 100 cm​2​, or 0.1
N/cm​2​.
➢ The pressure of the book on your hand is 0.1 N/cm​2​.
Force
Area
= P ressure
10 N
100 cm2
= 0.1 N /cm2
❖ A _______________ exerted over a _______________ area causes _______________
pressure than the _______________ force applied over a _______________ area.
❖ Air has _______________.
➢ One liter of air weighs about 0.01 N at sea level.
■
This is about the weight of a _______________ clip.
➢ The _______________ of Earth is at the _______________ of the
_______________.
➢ Air molecules are in _______________ motion and are _______________
towards Earth’s center of _______________.
➢ The _______________ of all these moving molecules causes air
_______________.
➢ Most of the air in the atmosphere is _______________ near Earth’s
_______________.
➢ So air pressure is _______________ near Earth’s surface and
_______________ as altitude _______________.
1. EXPLAIN: ​Why does air exert pressure on Earth’s surface?
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Elevation
❖ Air _______________ changes with _______________, or height above sea level.
➢ The atmosphere is hundreds of kilometers _______________.
➢ The weight of all this air causes _______________ pressure near the
_______________.
➢ This _______________ the air molecules _______________ together.
➢ Near the _______________ of the atmosphere, the air molecules remain
_______________ apart.
➢ There is very _______________ weight of air pressing down.
➢ Therefore, the air pressure is _______________.
➢ The _______________ the elevation, the _______________ the air pressure.
❖ Air pressure _______________ as distance above the surface _______________.
➢ The air pressure on _______________ of a mountain is _______________ than
the air pressure at _______________ level.
➢ Air pressure at sea level is about 10 N/cm​2​.
2. DESCRIBE: How does elevation affect air pressure?
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Water Vapor
❖ The _______________ water vapor in the air, the _______________ the air pressure.
➢ Water _______________ from lakes, rivers, and oceans.
➢ Living things _______________ off water vapor.
➢ All of this water vapor goes into the _______________.
➢ The lighter molecules of water vapor _______________ some of the other gas
molecules in air.
➢ Air with a lot of water vapor weighs _______________ than dry air with less
water vapor.
➢ Thus, _______________ air exerts _______________ pressure.
➢ Air pressure goes _______________ as the amount of water vapor in the air
_______________ up.
3. DESCRIBE: How does water vapor affect air pressure?
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Temperature
❖ Under ordinary conditions, the _______________ the temperature, the
_______________ the air pressure.
➢ Heat makes air molecules move _______________.
➢ As the molecules move _______________, they spread apart.
➢ This makes the air _______________ dense.
❖ So _______________ air is _______________ dense than cool air.
➢ In summer, when temperatures are _______________, the air pressure is
usually _______________.
4. RELATE: How is temperature related to air pressure?
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