# energy in the atmosphere

## the greenhouse effect

When sunlight heats Earths surface, some of the heat radiates back into the atmosphere. Some of this heat is absorbed by gases in the atmosphere. This is the greenhouse effect, and it helps to keep Earth warm. The greenhouse effect allows Earth to have temperatures that can support life. Gases that absorb heat in the atmosphere are called greenhouse gases. They include carbon dioxide and water vapor. Human actions have increased the levels of greenhouse gases in the atmosphere. This is shown in Figure 15.11. The added gases have caused a greater greenhouse effect. How do you think this affects Earths temperature?

## energy and latitude

Different parts of Earths surface receive different amounts of sunlight. You can see this in Figure 15.10. The Suns rays strike Earths surface most directly at the equator. This focuses the rays on a small area. Near the poles, the Suns rays strike the surface at a slant. This spreads the rays over a wide area. The more focused the rays are, the more energy an area receives and the warmer it is.

## conduction

In conduction, heat is transferred from molecule to molecule by contact. Warmer molecules vibrate faster than cooler ones. They bump into the cooler molecules. When they do they transfer some of their energy. Conduction happens mainly in the lower atmosphere. Can you explain why?

## convection

Convection is the transfer of heat by a current. Convection happens in a liquid or a gas. Air near the ground is warmed by heat radiating from Earths surface. The warm air is less dense, so it rises. As it rises, it cools. The cool air is dense, so it sinks to the surface. This creates a convection current, like the one in Figure 15.9. Convection is the most important way that heat travels in the atmosphere.

## what is energy

What explains all of these events? The answer can be summed up in one word: energy. Energy is defined as the ability to do work. Doing anything takes energy. A campfire obviously has energy. You can feel its heat and see its light.

## forms of energy

Heat and light are forms of energy. Other forms are chemical and electrical energy. Energy cant be created or destroyed. It can change form. For example, a piece of wood has chemical energy stored in its molecules. When the wood burns, the chemical energy changes to heat and light energy.

## movement of energy

Energy can move from one place to another. It can travel through space or matter. Thats why you can feel the heat of a campfire and see its light. These forms of energy travel from the campfire to you.

## energy from the sun

Almost all energy on Earth comes from the Sun. The Suns energy heats the planet and the air around it. Sunlight also powers photosynthesis and life on Earth.

## photons of energy

The Sun gives off energy in tiny packets called photons. Photons travel in waves. Figure 15.7 models a wave of light. Notice the wavelength in the figure. Waves with shorter wavelengths have more energy.

## electromagnetic spectrum

Energy from the Sun has a wide range of wavelengths. The total range of energy is called the electromagnetic spectrum. You can see it in Figure 15.8. Visible light is the only light that humans can see. Different wavelengths of visible light appear as different colors. Radio waves have the longest wavelengths. They also have the least amount of energy. Infrared light has wavelengths too long for humans to see, but we can feel them as heat. The atmosphere absorbs the infrared light. Ultraviolet (UV) light is in wavelengths too short for humans to see. The most energetic UV light is harmful to life. The atmosphere absorbs most of this UV light from the Sun. Gamma rays have the highest energy and they are the most damaging rays. Fortunately, gamma rays dont penetrate Earths atmosphere.

## how energy moves through the atmosphere

Energy travels through space or material. Heat energy is transferred in three ways: radiation, conduction, and convection.

Radiation is the transfer of energy by waves. Energy can travel as waves through air or empty space. The Suns energy travels through space by radiation. After sunlight heats the planets surface, some heat radiates back into the atmosphere.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

A campfire warms the campers sitting around it by conduction.

a. true

-->  b. false

When heat is transferred by the movement of electromagnetic waves it is called

a. convection

b. conduction

d. none of these

Energy can travel only through matter.

a. true

-->  b. false

Electromagnetic spectrum

a. is all visible to humans

-->  b. has the highest energy at the short wavelengths.

c. has the highest energy in the infrared.

d. is only able to travel through material

Most of the energy on Earth comes from the sun.

-->  a. true

b. false

The vertical movement of air due to the uneven heating is called

-->  a. convection

b. reflection

c. conduction

d. refraction

Wavelengths that are short and very high energy are

a. infrared

-->  c. ultraviolet

d. visible light

The electromagnetic spectrum is the range of wavelengths of visible light.

a. true

-->  b. false

Light with the most energy is infrared light.

a. true

-->  b. false

a. reflect back into space

b. be absorbed by clouds

c. strike the ground

-->  d. all of these

Gamma rays do not penetrate Earths atmosphere.

-->  a. true

b. false

Warmer molecules have more energy than cooler ones.

-->  a. true

b. false

Conduction happens mainly in the upper atmosphere.

a. true

-->  b. false

Warm air always sinks to the surface in a convection current.

a. true

-->  b. false

The greenhouse effect causes more solar energy to reach Earths surface.

a. true

-->  b. false

Energy cannot be created or destroyed.

-->  a. true

b. false

ability to do work

b. convection

c. ultraviolet light

d. photon

-->  e. energy

f. infrared light

g. conduction

Two important greenhouse gases are carbon dioxide and water vapor.

-->  a. true

b. false

tiny packet of energy

b. convection

c. ultraviolet light

-->  d. photon

e. energy

f. infrared light

g. conduction

transfer of energy by a current

-->  b. convection

c. ultraviolet light

d. photon

e. energy

f. infrared light

g. conduction

Sunlight hits Earth surface, then heat travels by conduction back into the atmosphere.

-->  a. true

b. false

transfer of energy by waves through air or empty space

b. convection

c. ultraviolet light

d. photon

e. energy

f. infrared light

g. conduction

Deep purple is part of the ultraviolet spectrum.

a. true

-->  b. false

Burning wood releases chemical energy.

-->  a. true

b. false

light with wavelengths too long for humans to see

b. convection

c. ultraviolet light

d. photon

e. energy

-->  f. infrared light

g. conduction

transfer of energy by direct contact between molecules

b. convection

c. ultraviolet light

d. photon

e. energy

f. infrared light

-->  g. conduction

light with wavelengths too short for humans to see

b. convection

-->  c. ultraviolet light

d. photon

e. energy

f. infrared light

g. conduction

Forms of energy include

a. electrical energy.

b. chemical energy.

c. light energy.

-->  d. all of the above

Which statement about energy is false?

a. Energy can change form.

-->  b. Energy can be created.

c. Energy can do work.

d. Energy can travel.

Convection occurs in

a. gases.

b. solids.

c. liquids.

-->  d. two of the above

Energy can travel through space by

a. conduction.

b. convection.

d. two of the above

Differences in solar energy by latitude result in

a. winds.

b. weather.

c. ocean currents.

-->  d. all of the above

A greenhouse gas mainly absorbs heat that

a. radiates directly from the sun.

-->  b. re-radiates from Earths surface.

c. comes from burning fossil fuels.

d. before it reaches Earths surface.

The greenhouse effect is caused

a. completely by human actions.

-->  b. partly by natural processes.

c. only by carbon dioxide.

d. two of the above

## diagram questions

No diagram questions associated with this lesson