the atmosphere

altitude and density

Altitude is height above sea level. The density of air decreases with height. There are two reasons. At higher altitudes, there is less air pushing down from above. Also, gravity is weaker farther from Earths center. So at higher altitudes, air molecules can spread out more. Air density decreases. You can see this in Figure 15.4.

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density of air

Density is mass per unit volume. Density is a measure of how closely molecules are packed together. The closer together they are, the greater the density. Since air is a gas, the molecules can pack tightly or spread out. The density of air varies from place to place. Air density depends on several factors. One is temperature. Like other materials, warm air is less dense than cool air. Since warmer molecules have more energy, they are more active. The molecules bounce off each other and spread apart. Another factor that affects the density of air is altitude.

properties of air

We usually cant sense the air around us unless it is moving. But air has the same basic properties as other matter. For example, air has mass, volume and, of course, density.

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particles in the air

Air includes many tiny particles. The particles may consist of dust, soil, salt, smoke, or ash. Some particles pollute the air and may make it unhealthy to breathe. But having particles in the air is very important. Tiny particles are needed for water vapor to condense on. Without particles, water vapor could not condense. Then clouds could not form and Earth would have no rain.

gases in air

Figure 15.3 shows the main gases in air. Nitrogen and oxygen make up 99 percent of air. Argon and carbon dioxide make up much of the rest. These percentages are the same just about everywhere in the atmosphere. Air also includes water vapor. The amount of water vapor varies from place to place. Thats why water vapor isnt included in Figure 15.3. It can make up as much as 4 percent of the air. Ozone is a molecule made of three oxygen atoms. Ozone collects in a layer in the stratosphere.

composition of air

Air is easy to forget about. We usually cant see it, taste it, or smell it. We can only feel it when it moves. But air is actually made of molecules of many different gases. It also contains tiny particles of solid matter.

the atmosphere and sound

Sound is a form of energy that travels in waves. Sound waves cant travel through empty space, but they can travel through gases. Gases in the air allow us to hear most of the sounds in our world. Because of air, you can hear birds singing, horns tooting, and friends laughing. Without the atmosphere, the world would be a silent, eerie place.

the atmosphere and weathering

Weather makes life interesting. Weather also causes weathering. Weathering is the slow wearing down of rocks on Earths surface. Wind-blown sand scours rocks like sandpaper. Glaciers of ice scrape across rock surfaces like a file. Even gentle rain may seep into rocks and slowly dissolve them. If the water freezes, it expands. This eventually causes the rocks to crack. Without the atmosphere, none of this weathering would happen.

altitude and air pressure

Like density, the pressure of the air decreases with altitude. There is less air pressing down from above the higher up you go. Look at the bottle in Figure 15.5. It was drained by a hiker at the top of a mountain. Then the hiker screwed the cap on the bottle and carried it down to sea level. At the lower altitude, air pressure crushed it. Can you explain why?

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air pressure

Because air is a gas, its molecules have a lot of energy. Air molecules move a lot and bump into things. For this reason, they exert pressure. Air pressure is defined as the weight of the air pressing against a given area. At sea level, the atmosphere presses down with a force of about 1 kilogram per square centimeter (14.76 pounds per square inch). If you are standing at sea level, you have more than a ton of air pressing against you. Why doesnt the pressure crush you? Air presses in all directions at once. Other molecules of air are pushing back.

the atmosphere and earths temperature

Gases in the atmosphere surround Earth like a blanket. They keep the temperature in a range that can support life. The gases keep out some of the Suns scorching heat during the day. At night, they hold the heat close to the surface, so it doesnt radiate out into space.

the atmosphere and the suns rays

The atmosphere protects living things from the Suns most harmful rays. Gases reflect or absorb the strongest rays of sunlight. Figure 15.1 models this role of the atmosphere.

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the atmosphere and living things

Most of the atmosphere is nitrogen, but it doesnt do much. Carbon dioxide and oxygen are the gases in the atmosphere that are needed for life. Plants need carbon dioxide for photosynthesis. They use sunlight to change carbon dioxide and water into food. The process releases oxygen. Without photosynthesis, there would be very little oxygen in the air. Other living things depend on plants for food. These organisms need the oxygen plants release to get energy out of the food. Even plants need oxygen for this purpose.

why the atmosphere is important

We are lucky to have an atmosphere on Earth. The atmosphere supports life, and is also needed for the water cycle and weather. The gases of the atmosphere even allow us to hear.

the atmosphere and weather

Without the atmosphere, there would be no clouds or rain. In fact, there would be no weather at all. Most weather occurs because the atmosphere heats up more in some places than others.

the atmosphere and earths water

Figure 15.2 shows the role of the atmosphere in the water cycle. Water vapor rises from Earths surface into the atmosphere. As it rises, it cools. The water vapor may then condense into water droplets and form clouds. If enough water droplets collect in clouds they may fall as rain. This how freshwater gets from the atmosphere back to Earths surface.

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instructional diagrams

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questions

The top four gases in Earths atmosphere include

a. helium.

b. hydrogen.

c. water vapor.

-->  d. carbon dioxide.

What are the two most common gases in the atmosphere?

a. hydrogen and oxygen

b. nitrogen and water vapor

c. hydrogen and nitrogen

-->  d. oxygen and nitrogen

The atmosphere is needed for all of the following except

a. weathering.

b. life on Earth.

-->  c. plate tectonics.

d. the water cycle.

The most important gas(es)for life are

a. nitrogen and oxygen

-->  b. oxygen and carbon dioxide

c. oxygen

d. nitrogen, oxygen and carbon dioxide

Plants need oxygen in order to

a. undertake photosynthesis.

-->  b. obtain energy from food.

c. make their own food.

d. breathe.

Photosynthesis

-->  a. uses carbon dioxide and creates oxygen

b. uses oxygen and creates carbon dioxide

c. uses carbon dioxide and oxygen and creates food energy

d. uses food energy and creates carbon dioxide and oxygen.

On the Moon

a. birds couldnt breathe

b. birds couldnt fly

c. if birds said "cheap" they wouldnt be heard

-->  d. all of these

Solid particles in the atmosphere

a. may include salt and ash.

b. may harm human health.

c. allow clouds to form.

-->  d. all of the above

Which property of air varies from sea level to the top of a high mountain?

a. state

-->  b. pressure

c. composition

d. all of the above

An increase in air pollutant particles

a. would have no effect on the number of raindrops

b. would have an unknown effect on the number of raindrops

-->  c. could produce more raindrops

d. might produce fewer raindrops

Without the atmosphere, Earth would have

-->  a. a greater range of temperatures.

b. more severe weather.

c. more glaciers.

d. two of the above

At sea level, the atmosphere presses down with a force of about

-->  a. 1 kg/cm2 .

b. 1 g/cm2 .

c. 1 lb/in2 .

d. 1 ton/in2 .

The atmosphere protects Earth from harmful solar rays.

-->  a. true

b. false

Sound waves travel rapidly through empty space.

a. true

-->  b. false

Carbon dioxide is abundant in the atmosphere.

a. true

-->  b. false

Ozone is a type of oxygen.

-->  a. true

b. false

Weather on the Moon is always stormy.

a. true

-->  b. false

Without the atmosphere, we could not hear most sounds.

-->  a. true

b. false

The main reason Earth can support life is its atmosphere.

-->  a. true

b. false

Earths atmosphere consists mainly of oxygen.

a. true

-->  b. false

Gases in the atmosphere are too thin to block any solar rays.

a. true

-->  b. false

The atmosphere is about 10 percent water vapor.

a. true

-->  b. false

Sound waves travel through empty spaces between air molecules.

a. true

-->  b. false

Solid particles in the atmosphere may include dust and soil.

-->  a. true

b. false

Clouds could not form if the air contained no solid particles.

-->  a. true

b. false

The density of air depends on how closely gas molecules are packed together.

-->  a. true

b. false

The density of air is greatest at high altitudes.

a. true

-->  b. false

third most common gas in Earths atmosphere

a. air pressure

b. altitude

c. sound

d. nitrogen

-->  e. argon

f. carbon dioxide

g. water vapor

gas in Earths atmosphere that varies in amount from place to place

a. air pressure

b. altitude

c. sound

d. nitrogen

e. argon

f. carbon dioxide

-->  g. water vapor

gas in Earths atmosphere that is needed for life

a. air pressure

b. altitude

c. sound

d. nitrogen

e. argon

-->  f. carbon dioxide

g. water vapor

weight of air pushing against a given area

-->  a. air pressure

b. altitude

c. sound

d. nitrogen

e. argon

f. carbon dioxide

g. water vapor

height above sea level

a. air pressure

-->  b. altitude

c. sound

d. nitrogen

e. argon

f. carbon dioxide

g. water vapor

main gas in Earths atmosphere

a. air pressure

b. altitude

c. sound

-->  d. nitrogen

e. argon

f. carbon dioxide

g. water vapor

form of energy that travels through matter in waves

a. air pressure

b. altitude

-->  c. sound

d. nitrogen

e. argon

f. carbon dioxide

g. water vapor

diagram questions

No diagram questions associated with this lesson