5.1 The Cat Family (Life Science) 5.2 Inside Sea Creatures (Life Science) 5.3 Staying Healthy (Life Science) 5.4 Food and Farming (Life Science) 5.5 Build an Aquarium (Life Science) 5.6 Changing World (Life Science) 5.7 Underwater Explorers (Earth Science) 5.8 Drought (Earth Science) 5.9 Mountains of the World (Earth Science) 5.10 Green Gardening (Earth Science) 5.11 Pioneers of Physics (Physical Science) 5.12 Baking Chemistry (Physical Science) 5.13 Building Science (Physical Science) 5.14 Generating Power (Physical Science) 5.15 The Light Bulb (Physical Science) 5.16 Telescopes (Space and Technology) 5.17 Moon Landings (Space and Technology) 5.18 Cars Present, Past, and Future (Space and Technology)
Trang 1Scott Foresman Science 5.14
Nonfi ction Predict • Labels
• Captions
• Diagrams
• Glossary
Forms of Energy
ISBN 0-328-13957-2 ì<(sk$m)=bdjfhg< +^-Ä-U-Ä-U
Scott Foresman Science 5.14
Nonfi ction Predict • Labels
• Captions
• Diagrams
• Glossary
Forms of Energy
ISBN 0-328-13957-2 ì<(sk$m)=bdjfhg< +^-Ä-U-Ä-U
Trang 21 How do batteries make our lives easier?
2 What is the purpose of an electric meter?
3 What are the benefi ts and drawbacks of the
use of fossil fuels as an energy source?
transmitted from power plants to homes and other buildings, its voltage has to be
increased, decreased, and regulated Write to explain how and why this happens Include examples from the book to support your answer
5 Predict Based on what you learned about
renewable resources, what types of energy
do you predict will become more important
in the future?
What did you learn?
Extended Vocabulary
circuit current fossil fuel generator geothermal energy hydroelectric energy nuclear fi ssion
renewable resources solar cells
turbine
Vocabulary
conduction
convection
electromagnetic radiation
energy
kinetic energy
potential energy
thermal energy
Picture Credits
Every effort has been made to secure permission and provide appropriate credit for photographic material
The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.
Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).
Opener: Lester Lefkowitz/Corbis; 4 (C) Warren Morgan/Corbis, (B) ©Bryan F Peterson/ Corbis; 7 ©Charles E Rotkin/Corbis;
8 ©Charles E Rotkin/Corbis; 11 (T) Lester Lefkowitz/Corbis; 14 Larry Lee Photography/Corbis;15 (T) Sally A Morgan/
Ecoscene/Corbis; 16 (B) Francesc Muntada/Corbis; 20 Attar Maher/Corbis; 22 ©Lester Lefkowitz/Corbis.
Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson
ISBN: 0-328-13957-2
Copyright © Pearson Education, Inc All Rights Reserved Printed in the United States of America
This publication is protected by Copyright, and permission should be obtained from the publisher prior to any
prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,
mechanical, photocopying, recording, or likewise For information regarding permission(s), write to
Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.
by Abbie Farara
Trang 3Chemical energy is energy that holds atoms together to form molecules Nuclear energy holds protons together to form the nucleus of an atom Sound energy is caused by particles vibrating, or moving back and forth, in a pattern called a wave Light is a form of electromagnetic radiation, which means that
it is a combination of both electrical and magnetic energy Thermal energy is created by the movement of particles inside matter Conduction, convection, and radiation are ways that thermal energy moves Conduction is the fl ow of thermal energy between objects that are touching Convection is the movement of warm liquids or gases to cooler areas Radiation
is the transfer of thermal energy through electromagnetic waves
We use electrical energy every day But where do we get it? People generate electricity in many ways All involve changing some other form of energy into electrical energy
Scientists defi ne energy as “the ability to do work or cause
a change.” Energy can change from one form to another, but
it cannot be created or destroyed There are many different
forms of energy They include sound, light, electrical,
magnetic, chemical, mechanical, nuclear, and thermal energy
Kinetic energy is the energy of motion The amount of
kinetic energy an object has depends on its speed and mass
Heavy, fast-moving objects have lots of kinetic energy Light,
slow-moving objects have less Kinetic energy can change
into other forms of energy For example, kinetic energy can
be changed into electric, sound, or thermal energy
Potential energy, sometimes called stored energy, is
energy that is not causing change right now, but could cause
change in the future A skier standing at the top of a steep
hill has potential energy As the skier begins to slide down
the hill, potential energy changes to kinetic energy Potential
energy can also be stored in a stretched rubber band or in
two magnets that tend to push each other away
A heavy, fast-moving truck has
a lot of kinetic energy
This power plant is turning chemical energy into electrical energy.
What You Already Know
Trang 4There is hardly anything we do that doesn’t rely on electricity We use it for light, heat, refrigeration, computer power, elevators, entertainment, and so on Factories depend
on electric power to make most of the things we use Beauty salons, restaurants, and laundromats all need electric power
to provide goods and services to customers Most of this electricity is supplied by power plants
Power cables built over train tracks provide the trains with electricity.
Hospitals rely on electricity They have backup sources in case the power goes out
Picture yourself in your house during a thunderstorm
You are working on an art project while listening to
the radio Your brother is watching television Your
grandmother is in the kitchen, baking a cake Several
lights are on in the house You notice that the storm is
getting worse when you see a streak of lightning in the sky
Suddenly, the house is dark and silent You look outside
and see that the streetlights are off and all the other houses
are dark too Lightning has struck a power line and shut off
the electricity in your neighborhood
Cellular phones run on batteries
Batteries are a handy way of storing electricity They let us take power wherever we go The electricity is stored in layers of special chemicals
How many things in your household run on batteries?
Trang 5Power Plants
Power plants need a source of energy to produce
electricity This source of energy might be a fossil fuel such
as coal, oil, or natural gas These plants use the heat energy
from burning fuel to make steam, which is used to make
electricity The movement of wind and water is a source of
energy for some power plants Others use nuclear energy or
the heat of rocks deep beneath the ground
At a coal-fi red power
station, burning coal
heats water into steam,
which drives a turbine.
Any of these sources of energy can be used to spin a turbine A turbine takes kinetic energy and transfers it to a generator, which makes electricity The kinetic energy may come from wind or moving water Or it may come from steam made by burning fossil fuels Turbines have many blades attached to a shaft, or rod Kinetic energy turns the blades on the turbine, which rotates the shaft The shaft is connected to the generator The spinning movement of the shaft drives the generator
About 70 percent of the electricity used in the United States is produced using coal, oil, or gas as a source of energy
20 percent is made using nuclear energy About 7 percent is produced by hydroelectric, or water, energy The remaining
3 percent is made by wind and other types of energy
At a hydroelectric dam,
fl owing water from a river
is used to spin a turbine.
Trang 6The picture below shows a simple homemade generator The two magnets create a magnetic fi eld A wire is bent into a square coil and held on a rod The rod holds the square coil in the magnetic fi eld and allows it to spin As the coil spins, it creates an electric current The current fl ows through the wires and into the meter, which shows how strong the electricity is
Generators
A generator is a machine that converts kinetic energy
into electrical energy In a power plant, a turbine spins a
coil of wire inside the generator The coil is surrounded
by magnets As the coil spins, it generates a small
electric current in each section of its wire Together
these currents create a large amount of electricity The
electricity fl ows out of the generator to begin its journey
to homes, factories, and businesses
You may have seen a tiny generator such as this on an older bicycle It transforms the movement of the wheel into electricity, which powers the headlights When you ride a bike with a generator, you have to turn the pedals
a bit harder to provide the energy that is changed into electricity.
Bicycle Generator
wires run under board
meter registers voltage
wire coil spins between magnets
The wire and magnets in this homemade generator create
an electric current
Many power plants have several generators
magnets
Trang 7Next the current reaches substations that contain other transformers These are called step-down transformers because they reduce voltage A device called a regulator bank maintains the proper voltage
Then the power is split off in different directions Power lines carry the electricity
to individual buildings While most power lines are on poles, some are buried underground
A distribution grid is all the wiring, transformers, and other
equipment that connects a power plant to the buildings
it supplies First the electricity goes into transformers that
increase its voltage These are called step-up transformers
Then it travels through high-voltage wires.
Distribution Grid
power
station
industry power
lines
homes
pylons step-down
transformer
step-up
transformer
So how does the electricity from a power plant get to
homes, schools, and businesses? Transformers and wires
connect power plants to all these places
First the electric current from a generator goes into a
transformer A transformer is a large machine that increases
the voltage, or strength, of the electric current When
electric power is carried long distances, the voltage is
increased to a very high level Weak currents can’t travel
long distances efficiently Power lines on pylons, or towers,
carry the high-voltage power for hundreds of miles
Electricity Supply
The symbol on this sign indicates high voltage It is placed in locations to warn people of high electric voltage.
An engineer checks the voltage at a power substation.
Trang 8Electricity travels through a building in a circuit, or circular pathway Wires travel to each room and connect to outlets
Outlets are the places where you plug in things that use electricity
Buildings are fi tted with safety devices to prevent fi re due to an electrical overload
Circuit breakers cut off the electricity whenever the current increases to an unsafe level The power is turned back
on by fl ipping a switch In cars and some appliances, fuses do the same job as circuit breakers
Fuses burn out when too much power fl ows through them, stopping the fl ow of electricity
A dishwasher needs electricity to run
Fuses such as these are found in appliances and cars They must
be replaced when they burn out.
When electricity reaches a building, the voltage is
decreased further A transformer drum attached to a pole
reduces the voltage for normal household use If power lines
in an area are buried underground, separate transformer
boxes are used for each home
Electric power enters a house or other building through
a meter People have to pay the electric company for power
The meter keeps track of the amount of electricity used
and how much it costs Electric wires run from the meter
through the walls of a building One wire carries electricity
to each light switch, outlet, or electric socket
Electricity in the Home
outlet
lighting circuit
meter
circuit
breaker
This diagram shows the circuit
of electricity in a house
Notice the meter, the fuse
box, and the sockets
Trang 9natural gas
Open-cast mining is
a way to mine coal that makes huge holes in the ground.
Power plants need energy to produce electricity Much
of this energy comes from coal, oil, or natural gas These
resources are known as fossil fuels
Millions of years ago, much of the Earth was covered
with swamps When the plants living in the swamps died,
their remains decayed and turned
into a brown, spongelike matter
called peat Over time, layers
of soil, rock, and volcanic ash
buried the peat Pressure
and heat changed the
peat into coal Oil
was formed through
a similar process
Fossil Fuels
Coal is removed from the Earth by mining In underground mines, a series of deep tunnels reach coal beds deep in the Earth In surface mines, layers of soil only a few feet deep are removed Oil and natural gas are removed by drilling Fossil fuels are widely used because they are easy to fi nd and collect However, fossil fuels cause serious problems Burning coal causes smog and other forms of pollution Oil spills damage the environment Most scientists believe the burning of fossil fuels is damaging Earth’s atmosphere Also, fossil fuels are not renewable, so once they are used up, they can’t be replaced
crude oil
coal
Fossil fuels come in liquid form (oil), solid form (coal), and gaseous form (natural gas).
This oil rig is set
up over the ocean
Pipelines or ships carry the oil and gas
to refi neries.
Trang 10Nuclear Fission
A dome of concrete and steel surrounds this nuclear reactor It allows the nuclear reaction to be used safely.
neutron
nucleus
nucleus splits energy
neutrons
Another form of energy used to produce electricity is
nuclear power About 20 percent of the electricity used in
the United States comes from nuclear power In the 1930s,
scientists learned to split atoms They found that this
process, called nuclear fi ssion, releases huge amounts of
energy Nuclear fi ssion was fi rst used for weapons during
World War II After the war, scientists discovered how to
use fi ssion to make electricity
In nuclear fi ssion, atoms of an element called uranium
are split, releasing huge amounts of energy This energy
boils water to make steam The steam turns a turbine, which
causes the generator to make electricity The steam is then
cooled and recycled through the system to be used again
Nuclear power is a relatively dependable, clean, and
inexpensive source of power However, the waste from
nuclear power plants must be disposed of very
carefully, or else it can make people sick
Nuclear Power
When atoms are split, neutrons are released The neutrons hit other atoms, causing them to split It’s similar
to the way one bowling ball knocks down all the pins
Fission releases so much energy that only a small amount
of uranium is needed
Trang 11The movement of the wind
turns the blades on a wind
turbine The generator
at the top of the turbine
changes this movement into
electricity The electricity is
then sent through cables to
locations where it is used
Wind Turbines
blade generator
As the demand for energy in the world increases, the
search for renewable energy sources has become more
important The supply of fossil fuels is running out quickly
Several sources of renewable energy are used in parts
of the world today These sources include wind energy,
hydroelectric energy, tidal energy, geothermal energy, and
solar energy There are both benefi ts and drawbacks to the
use of each source
Some wind turbines work on their own, while others work
in groups called wind farms.
Wind power is clean, readily available, and does not harm the environment However, since many people think that turbines are ugly or noisy, they don’t want them in their neighborhoods As a result, turbines may be placed far from areas where people live
Renewable Energy