Introduction To Energy Page 3
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1
2
3
4Electricity
is energy stored in objects by the
Stored Mechanical Energy
application of a force. Compressed springs and stretched rubber
Electricity is different from the other energy sources because it is
bands are examples of stored mechanical energy.
a secondary source of energy. We must use another energy source
Nuclear Energy
is energy stored in the nucleus of an atom; it is the
to produce electricity. In the U.S., coal is the number one energy
energy that holds the nucleus together. The energy can be released
source used for generating electricity.
when the nuclei are combined or split apart. Nuclear power plants
Electricity is sometimes called an
energy carrier
because it is an
split the nuclei of uranium atoms in a process called
fission
. The sun
efficient and safe way to move energy from one place to another,
combines the nuclei of hydrogen atoms in a process called
.
fusion
and it can be used for so many tasks. As we use more technology,
Gravitational Energy
is the energy of position or place. A rock
the demand for electricity grows.
resting at the top of a hill contains gravitational potential energy.
Hydropower, such as water in a reservoir behind a dam, is an
example of gravitational potential energy.
Conservation of Energy
U.S. ENERGY CONSUMPTION BY SOURCE, 2008
To scientists,
conservation of energy
is not saving energy. The law
of conservation of energy says that energy is neither created nor
destroyed. When we use energy, it doesn’t disappear. We change it
from one form of energy into another.
A car engine burns gasoline, converting the chemical energy in
NONRENEWABLE
RENEWABLE
gasoline into mechanical energy. Solar cells change radiant energy
into electrical energy. Energy changes form, but the total amount of
energy in the universe stays the same.
Energy Efficiency
PETROLEUM
37%
BIOMASS
3.9%
Uses: transportation,
Uses: heating, electricity,
Energy efficiency is the amount of useful energy you get from a
manufacturing
transportation
system. A perfect energy-efficient machine would change all the
energy put in it into useful work—a technological impossibility
today. Converting one form of energy into another form always
involves a loss of usable energy.
Most energy transformations are not very efficient. The human
COAL
22.6%
HYDROPOWER
2.5%
body is a good example. Your body is like a machine, and the fuel for
your machine is food. Food gives you the energy to move, breathe,
Uses: electricity, manufacturing
Uses: electricity
and think.
Your body isn’t very efficient at converting food into useful work.
Your body’s overall efficiency is about 15 percent most of the time.
The rest of the energy is lost as heat. You can really feel that heat
when you exercise!
NATURAL GAS
23.5%
GEOTHERMAL
0.4%
Uses: heating, manufacturing,
Uses: heating, electricity
Sources of Energy
electricity
We use many different energy sources to do work for us. They are
classified into two groups—renewable and nonrenewable.
In the United States, most of our energy comes from
nonrenewable
energy sources
. Coal, petroleum, natural gas, propane, and
URANIUM
8.5%
WIND
0.5%
uranium are nonrenewable energy sources. They are used to make
Uses: electricity
Uses: electricity
electricity, heat our homes, move our cars, and manufacture all
kinds of products. These energy sources are called nonrenewable
because their supplies are limited. Petroleum, for example, was
formed millions of years ago from the remains of ancient sea plants
and animals. We can’t make more crude oil deposits in a short time.
PROPANE
1%
SOLAR
0.1%
Renewable energy sources
include biomass, geothermal energy,
hydropower, solar energy, and wind energy. They are called
Uses: heating, manufacturing
Uses: heating, electricity
renewable because they are replenished in a short time. Day after
day, the sun shines, the wind blows, and the rivers flow. We use
Source: Energy Information
renewable energy sources mainly to make electricity.
Administration
7
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1.800.875.5029
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