Transcript Slide 1

Physical
Physics
The Study of How Matter Behaves
Physics is the branch of science that concerns
the behavior of matter in our world—the forces
that cause matter to behave as it does. Physics
helps to explain how cellular molecules can
move from a lower concentration in an
organism to a higher one, how ocean tides
occur, and how matter exists in the states of a
solid, liquid, or gas. (page 555)
Physical Science
Physics
The Study of How Matter Behaves
Many of the properties and behaviors of
matter can be explained by force and
energy. A force shows the presence of
energy in an environment. Energy is the
capacity to do work. The area of physics
that deals with forces, energy, and their
effect on bodies is mechanics. (page 555)
Physical Science
Physics
The Study of How Matter Behaves
Physical Science
Physics
Mechanics
The study of mechanics was one of the first
sciences developed. Ancient Greek philosopher
and scientist Aristotle theorized that heavy
bodies fall faster than light bodies. This theory
was proved false in the early 17th century by
Italian scientist and mathematician Galileo, who
dropped items of different weights from the
leaning tower of Pisa. (page 556)
Physical Science
Physics
Mechanics
Physical Science
Physics
Mechanics
The force acting upon the objects was not
fully understood, however, until
Englishman Sir Isaac Newton formulated
laws of gravity and motion that explained
how different forces act on objects. (page
556)
Physical Science
Physics
Mechanics
Physical Science
Physics
Mechanics
Physical Science
Physics
The Force of Gravity
Gravity is the most commonly experienced of all
forces in nature. The presence of gravity was first
proposed by Newton when he observed the
motion of an apple falling from a tree. On the basis
of this simple observation, he developed the Law
of Universal Gravitation, which holds that every
body having a mass exerts an attractive force on
every other body having a mass in the universe.
(page 556)
Physical Science
Physics
The Force of Gravity
The strength of the force depends on the masses of
the objects and the distance between them. (Mass is
the measure of the amount of matter in an object.)
Thus, the apple's falling illustrates the gravitational
pull (attraction) of the larger Earth on the smaller
apple. The Law of Universal Gravitation also explains
how the planets, attracted by the much larger Sun,
remain in their orbits as they revolve around it. (page
556)
Physical Science
Physics
NEWTON'S THREE LAWS OF MOTION
The Law of Inertia
A body remains at rest or continues in a state of
uniform motion unless a force acts on it. For
example, when you drive a car and suddenly
jam on the brakes, you continue to move
forward. This is because your body's tendency
is to remain in the same state of uniform motion
(moving forward). The brakes were applied to
the car, so its uniform motion was changed.
(page 556)
Physical Science
Physics
NEWTON'S THREE LAWS OF MOTION
The Law of Applied Force
A body's change in speed and direction is
proportional to the amount of force
applied to it. For example, the vanes on a
windmill, which move by the force of the
wind, will accelerate according to the
speed and direction of the wind that drives
them. (page 556)
Physical Science
Physics
NEWTON'S THREE LAWS OF MOTION
The Law of Action and Reaction
For every action there is an equal but
opposite reaction force. For example, a
gun's muzzle kicks backward when a
bullet is discharged from it. (page 556)
Physical Science
EXERCISE 1
Laws of Force and Motion (page 557)
Directions: Identify the following statements as (G) illustrating Newton's
Law of Universal Gravitation, (I) applying to the Law of Inertia, (AF)
applying to the Law of Applied Force, or (AR) applying to the Law of
Action and Reaction.
1. ____ A ball on a pool table rebounds off another ball it just hit.
2. ____ A rocket is propelled upward by the powerful downward
discharge of exhaust gases.
3. ____ A bullet fired into the air eventually falls to the ground.
4. ____ A pendulum in a clock, once set in motion, continues to swing,
thereby regulating the clock's movement.
5. ____ A jet airplane, upon landing, lowers the flaps on its wings. The
flaps create drag, a force that reduces lift and helps the plane to slow
down.
Physical Science
EXERCISE 2 (page 557)
The Force of Gravity
Directions: Read the paragraph below and answer the questions that follow.
An astronaut weighs in before blast-off. He weighs only a fraction of his
original weight when he steps on a scale on the moon. Journeying to
Jupiter, he finds that his weight has increased several times over his original
weight.
1. How may these changes in weight be best explained?
(1) the amount of force each planetary body exerts as the astronaut weighs
himself
(2) the distance from the Sun of the planetary bodies on which he weighs
himself
(3) changes in the atmospheric pressure on the different heavenly bodies
(4) the amount of calories consumed during the flight
(5) the duration of time that elapsed between weigh-ins
2. What do you estimate the weight change for the same astronaut would
be if he were to land on Mercury?
Physical Science
Work, Energy, and Power
According to physics, work occurs when a
force succeeds in moving an object it acts
upon. For example, a person who lifts a
50-pound weight one foot off the floor is
performing work. For work to be
performed, the movement of the object
must be in the same direction as the
force—in this case vertical. (page 558)
Physical Science
Work, Energy, and Power (page 558)
Work may be expressed as any force unit
times any distance unit and may be written
as follows:
W = FxD
The amount of work done is the amount of
force multiplied by the distance moved. In
the preceding example, 50 foot-pounds of
work is done when 50 pounds are lifted one
foot:
50 lb x 1 ft = 50 ft lb
Physical Science
Work, Energy, and Power
Energy is required to do work. In the
example above, muscular energy is
illustrated in the form of a body that is
capable of doing work. Energy may be
classified as either kinetic or potential
energy. (page 558)
Physical Science
Work, Energy, and Power
Kinetic energy is energy possessed by a
body in motion. The form of energy shown
by a moving train is kinetic energy.
(page 558)
Physical Science
Work, Energy, and Power
Potential energy is energy that is stored
or is available for use by a body. For
example, coal has potential energy that is
released only when it is burned. A boulder
positioned on a hilltop has potential
energy before it is released. When the
boulder is pushed, its potential energy
becomes kinetic. (page 558)
Physical Science
Work, Energy, and Power
Power is the rate at which work is done.
Power is generally measured in
horsepower, which is equal to 550 footpounds per second or 33,000 footpounds
per minute. (page 558)
Physical Science
The Law of Conservation of Energy
The Law of Conservation of Energy holds
that all of the energy of the universe is
conserved. The capacity for energy to do
work can be changed from one kind to
another, but it cannot be lost. This
principle can be illustrated in the following
example of energy generated from a
waterfall. (page 558)
Physical Science
The Law of Conservation of Energy
Water possesses potential energy. When water
moves rapidly in a downward motion, drawn by
the pull of gravity, the potential energy is
changed into kinetic energy. Kinetic energy
from a waterfall can be harnessed to power a
turbine, a rotary engine, creating rotational
energy. This is sufficient to generate electrical
energy, which in turn is converted into light and
heat energy, which we use in our homes. The
initial potential energy has been changed into
five different forms. (page 558)
Physical Science
EXERCISE 3
Forms of Energy (page 559)
Directions: Identify the following statements as
either demonstrating kinetic energy (K) or
demonstrating potential energy (P).
1. ____ a strong west wind blowing across a
region
2. ____ a stick of unlit dynamite
3. ____ a hamburger
4. ____ a waterfall
Physical Science
EXERCISE 4
Types of Energy (page 559)
Directions: Read the following definitions of the five
types of energy. Then choose the best answers for the
questions below.
nuclear energy - energy from splitting an atom or
fusing atoms
chemical energy - energy from the reaction of two or
more substances combining with one another
electrical energy-energy from an electric current
solar energy - energy from the heat of the Sun
steam energy - energy from steam pressure
Physical Science
EXERCISE 4
Types of Energy (page 559)
1. Which form of energy results from the
fission of uranium-235 nuclei that is used to
generate electrical power?
(1) nuclear energy
(2) chemical energy
(3) electrical energy
(4) solar energy
(5) steam energy
Physical Science
EXERCISE 4
Types of Energy (page 559)
2. Which form of energy results from the
ignition of a gas and air mixture and
powers a car?
(1) nuclear energy
(2) chemical energy
(3) electrical energy
(4) solar energy
(5) steam energy
Physical Science
Simple Machines
A machine is a device that transmits or
multiplies force. A machine operates on
the principle of a little force as being
applied through a great distance and a
great resistance being overcome through
a short distance. (page 560)
Physical Science
Simple Machines
The lever
Physical Science
Simple Machines
The lever
Physical Science
Simple Machines
A lever is a simple machine used to
perform work by lifting a great weight. A
lever is just a bar that is free to pivot on its
support (called a fulcrum). Through the
use of a lever, for example, a 1,000-pound
weight can be lifted with relatively little
effort (force). (page 560)
Physical Science
Simple Machines (page 560)
The illustration above shows that it would
take 100 pounds of force for a person to
lift a 1,000-pound weight positioned 1 foot
from the fulcrum when the lever bar is 10
feet long. This may be expressed as
follows:
1,000 lbx1 ft = 100lbx10ft
Physical Science
Simple Machines
In this case a relatively small force (100
lb) applied at a great distance from the
object (10 ft) is able to overcome great
resistance (1,000 lb). According to this
principle the greater the distance between
the fulcrum and the applied force, the less
force required to perform the work. (page
560)
Physical Science
Simple Machines
The wheelbarrow,
the crowbar, the
pulley, and the
inclined plane are
simple machines.
Complex machines
are made up of more
than one simple
machine. (page 560)
Physical Science
EXERCISE 5
Simple Machines (page 561)
Directions: Choose the best answer for
each of the following questions.
1. According to the principle that a little
force applied through a great distance can
overcome great resistance, which would be
most likely to happen if the lever bar in the
preceding illustration is increased to 20 feet
in length and the weight remained at the end
of the bar?
Physical Science
EXERCISE 5
Simple Machines (page 561)
(1) The effort to lift the weight would increase to
150 pounds of applied force.
(2) The effort to lift the weight would remain at
100 pounds of applied force.
(3) The effort would be decreased by half, to 50
pounds of applied force.
(4) The resistance of the weight would double.
(5) The resistance of the weight would triple.
Physical Science
EXERCISE 5
Simple Machines (page 561)
2. What are some other types of
household items that could be considered
levers? (Hint: Any tool that makes the job
easier is likely a lever.)
Physical Science
The Nature of Heat and Energy
Today we know that heat is the result of
the random motion of molecules. It is
nothing more than energy itself. One
theory of physics that has contributed
greatly to our understanding of the
phenomenon of heat is kinetic theory, a
basic theory that explains how different
states of matter can exist. (page 561)
Physical Science
The Nature of Heat and Energy
The Kinetic Theory of Matter
According to the Kinetic Theory of Matter,
matter exists in three states— solid, liquid,
or gas. A fourth state, plasma, is an
ionized gas; the Sun is made up of
plasma. The form, or phase, of matter is
determined by the motion of the
molecules within it. (page 561)
Physical Science
The Nature of Heat and Energy
The Kinetic Theory of Matter
Physical Science
The Nature of Heat and Energy
The Kinetic Theory of Matter
Solids are composed of atoms or
molecules in limited motion. These atoms
or molecules are in direct contact with one
another, allowing little or no space for
random movement. The attractive forces
of the particles keep the solid intact and
give the solid its definite shape and
structure. (page 561)
Physical Science
The Nature of Heat and Energy
The Kinetic Theory of Matter
In liquids, individual atoms or molecules
are able to move past one another into
new positions, giving this form of matter
its fluidity. Cohesive forces hold liquids
intact. (page 561)
Physical Science
The Nature of Heat and Energy
The Kinetic Theory of Matter
Gases are substances in which the
individual atoms or molecules are in
constant random motion. The motion, or
kinetic energy, increases along with an
increase in temperature. Molecules are
unable to hold together, and this property
gives gases the ability to flow or spread out
to fill the container in which they are placed.
(page 562)
Physical Science
The Nature of Heat and Energy
Heat, Temperature, and the States of
Matter
The state of matter depends on its heat
content. Temperature is a measure of heat
intensity. The change from one state of
matter to another involves the addition or
subtraction of a certain amount of heat
per gram of substance. (page 562)
Physical Science
The Nature of Heat and Energy
Heat, Temperature, and the States of Matter
For example, at 32 degrees Fahrenheit,
water, a liquid, changes to ice, a solid. When
the temperature is raised above 32 degrees
Fahrenheit, the ice, a solid, changes to
water, a liquid. At temperatures at or above
212 degrees Fahrenheit, the boiling point of
water, the water changes to steam, a
gaseous state. Impurities in water affect its
freezing point. (page 562)
Physical Science
The Nature of Heat and Energy
Heat, Temperature, and the States of Matter
Certain materials expand when their
temperatures are raised and shrink when
they are lowered. Liquids expand more
noticeably than solids, but gases expand
even more. The mercury thermometer
employs this principle. Temperature can be
measured in degrees centigrade or degrees
Fahrenheit. (page 562)
Physical Science
The Nature of Heat and Energy
Heat, Temperature, and the States of
Matter
On the centigrade (or Celsius) scale, 0
degrees represents the freezing point of
water, and 100 degrees is the boiling
point. On the Fahrenheit scale, 32
degrees represents the freezing point of
water, and 212 degrees is the boiling
point. (page 562)
Physical Science
The Nature of Heat and Energy
Heat, Temperature, and the States of Matter
Temperature is measured in degrees by
thermometer, and heat is measured by the
calorie or British Thermal Unit (BTU). A
calorie is the amount of heat needed to raise
one gram of water one degree centigrade.
The BTU is the amount of heat required to
raise one pound of water 1 degree
Fahrenheit. (page 562)
Physical Science
The Nature of Heat and Energy
Heat, Temperature, and the States of
Matter
Physical Science
The Nature of Heat and Energy
Heat, Temperature, and the States of
Matter
Heat is transferred by three methods. The
first is called conduction, the transfer of
heat between objects that are in direct
contact. You have experienced this
whenever you have picked up a hot item,
such as a handle on a heated pan. The
second method is convection. (page 562)
Physical Science
The Nature of Heat and Energy
Heat, Temperature, and the States of Matter
This method depends on the currents of
water and air. When you are adding hot
water to one end of the bathtub filled with
water, convection transfers the heat to the
rest of the water. The third method is
radiation. You can feel waves of heat by
putting your hands near a radiator (used to
heat many apartments). (page 562)
Physical Science
The Nature of Heat and Energy
Heat, Temperature, and the States of Matter
Physical Science
EXERCISE 6
Kinetic Theory of Matter (page 563)
Directions: Identify the following statements as either
true (T) or false (F). 1. ___ There is more rigid
molecular structure in a solid than in a gas.
2. ___ An increase in temperature decreases the
molecular motion of a gas.
3. ___ Molecules moving past each other in a liquid
give it fluidity.
4. ___ Molecules in a gas are close together and
exhibit little motion.
5. ___ Heat is transferred by conduction, convection,
or coercion.
Physical Science
EXERCISE 7
Heat and Temperature
Directions: Read the passage below and
answer the questions that follow.
Different materials expand at different
degrees of temperature change and in
different percentages of their length,
volume, or surface. (page 564)
Physical Science
EXERCISE 7
Heat and Temperature
Buckling can occur when a material such as
asphalt used for road surfaces reacts to
changes in temperature, causing potholes.
This is one of the reasons for the
widespread use of reinforced concrete
(concrete with a steel framework) rather than
asphalt on road surfaces and the use of
reinforced concrete in high-rise apartment
construction. (page 564)
Physical Science
EXERCISE 7
Heat and Temperature
Physical Science
EXERCISE 7
Heat and Temperature (page 564)
1. What does the widespread use of reinforced concrete in
construction suggest?
(1) Concrete and steel expand and contract at nearly the
same temperatures.
(2) Reinforced concrete expands at temperatures much
higher than ordinary asphalt and does not buckle.
(3) Reinforced concrete does not expand and contract at all.
(4) Asphalt can be used only on roadways and never in
construction.
(5) Asphalt is much more expensive and harder to use than
concrete.
Physical Science
EXERCISE 7
Heat and Temperature (page 564)
2. Which heat transfer method is
demonstrated when your hand is positioned
directly over the flame of a lighted candle?
(1) convection
(2) conduction
(3) radiation
(4) expansion
(5) coersion
Physical Science
The Nature of Waves
A wave is a periodic or harmonic
disturbance in space or through a medium
(water, for instance) by which energy is
transmitted. Water, sound, and light all
travel in waves. The illumination a lamp
provides comes from light waves (a form
of electromagnetic waves) while the music
emanating from a stereo comes from
sound waves. (page 565)
Physical Science
The Nature of Waves
Wave
Physical Science
The Nature of Waves
The powers to preserve food and warm it
come from electromagnetic waves, and
the power that transmits signals to a
television set comes from radio waves
(another form of electromagnetic waves).
The energy that gives a waterbed its
soothing motion comes from water waves.
(page 565)
Physical Science
The Nature of Waves
Types and Properties of Waves
Waves transmit energy in different ways,
and all phases of matter transmit waves.
An example of a solid transmitting wave
energy is an earthquake that takes place
when rocks are under pressure and snap
or slide into new positions. Waves that are
felt and seen in water are examples of a
liquid transmitting wave energy. (page 565)
Physical Science
The Nature of Waves
Types and Properties of Waves
Gases also transmit wave energy, as in an
explosion, when heat, sound, and light
waves are generated. Two basic types of
waves exist: longitudinal waves and
transverse waves. (page 565)
Physical Science
The Nature of Waves
Types and Properties of Waves
Longitudinal wave
Particles of the medium move back and
forth in the same direction as the wave
itself moves. An example of a longitudinal
wave is a sound wave that occurs when a
tuning fork is tapped, as shown below.
(page 565)
Physical Science
The Nature of Waves
Types and Properties of
Waves (page 565)
LONGITUDINAL WAVE
When a tuning fork is
tapped, the prongs move
from right to left in a rapid
periodic motion. A sound
wave is produced, and it
moves parallel (right and
left) to the moving prong.
Physical Science
The Nature of Waves
Types and Properties of Waves (page
565)
Transverse wave
Particles of the medium move at right
angles to the direction of the wave's
movement. An example of a transverse
wave is one that occurs when a pebble is
tossed into a still pond. Light travels in
transverse waves. (Page 565)
Physical Science
The Nature of Waves
Types and Properties of
Waves (page 565)
TRANSVERSE WAVE
When a stone is dropped
into a pond, the waves
produced appear to
move outward. These
waves move at right
angles to the dropped
stone. (page 565)
Physical Science
The Nature of Waves
Waves have two components, a crest and
a trough. A crest is the point of highest
displacement in a wave, and the trough is
the point of lowest displacement. Crests
and troughs are easily visible in water
waves. (page 566)
Physical Science
The Nature of Waves
Physical Science
The Nature of Waves
Two specific characteristics of a wave are
length and frequency:
• Wavelength is defined as the distance
between two successive wave crests or
two successive wave troughs.
• Wave frequency is the number of wave
crests that pass a given point per second.
(page 566)
Physical Science
The Nature of Waves
Therefore, the shorter the wavelength, the
higher the wave frequency. In fact, a wave's
speed equals the wavelength times the wave
frequency.
When a source of a wave is in motion, a
compression of the wavelength is detected.
This can be demonstrated with sound waves.
As a train passes you by while you are standing
on the platform, you will notice a distinct drop in
the pitch or sound quality. (page 566)
Physical Science
The Nature of Waves
This drop in sound pitch is heard by the
observers standing on the side during an
automotive race such as the Indianapolis 500.
Water waves demonstrate the same
compression in the direction of motion. The
water waves in the front of a boat are squeezed
together, while those at the rear of the boat are
far apart. This is referred to as the Doppler
Effect. Scientists use the Doppler Effect to
forecast tornadoes and to detect the motions of
stars in our galaxy. (page 566)
Physical Science
The Nature of Waves
Physical Science
The Nature of Waves
Sound waves, as illustrated above, are
longitudinal waves. A musical pitch, or tone, is
heard when there is a definite frequency to a
wave. The lower the frequency, the lower the
tone. For example, the frequency of a bass
speaker in a stereo system is lower than a
tweeter, or high-frequency speaker, because
the low-pitched sound of the bass results from
a lower number of vibrations per second. (page
566)
Physical Science
The Nature of Waves
A sound wave is a wave of compression.
It begins at a source—in the case above,
a horn speaker. The speaker vibrates,
compressing the air in front of it and, like
a spring, pushes it away. As the wave
passes, the air molecules are forced
together. The sensation of hearing results
when these waves strike the eardrum.
(page 566)
Physical Science
The Nature of Waves
Sound waves can travel through solids,
liquids, and gases. In fact, the human
body can be a medium for sound waves.
Ultrasonic waves, very high-pitched
waves, are used in medicine today to
detect diseases or to show images of
unborn fetuses. (page 566)
Physical Science
EXERCISE 8 (page 567)
Wave Types
Directions: In the space provided, write L if the
example is an example of a longitudinal wave and T if
it is an example of a transverse wave.
1. ____ a wave that can be seen when a loose rope
held end to end is jerked at one end
2. ____ the noise caused by the detonation of an
atomic bomb
3. ____ the hum created when an arrow is released
from a bow
4. ____ waves that appear on the surface of the
ocean
Physical Science
EXERCISE 9
Properties of Waves (page 567)
Directions: Look at the illustration below
and choose the best answers to the
questions that follow.
Physical Science
EXERCISE 9
Properties of Waves (page 567)
1. According to the illustration above, which
points could be used to measure
wavelength?
(1) T and Y
(2) X and Y
(3) Z and Y
(4) V and W
(5) T, X, and U
Physical Science
EXERCISE 9
Properties of Waves (page 567)
2. The Doppler Effect is used for which
of the following purposes?
(1) to find fish in lakes
(2) to predict storms and tornadoes
(3) to test wave frequency
(4) to reflect images to satellites
(5) to heighten sound in stereos
Physical Science
The Nature of Light
Physicists define light as a form of
electromagnetic energy that stimulates
sensitive cells of the retina of the human
eye to cause perception of vision.
Electromagnetic energy can be expressed
in wavelength ranges along a continuum,
or spectrum. Light occupies the center of a
spectrum that ranges from the low end
(gamma rays) to the high end (radio
waves). (page 568)
Physical Science
The Nature of Light
Electromagnetic Spectrum
Physical Science
The Nature of Light
Electromagnetic Spectrum
Physical Science
The Nature of Light
The other rays that occupy the
electromagnetic spectrum are Xrays,
ultraviolet rays, and infrared rays.
Ultraviolet rays are invisible and are
chiefly responsible for sunburn and tan.
Heat-emitting objects such as the sun or a
radiator send out infrared rays that can be
detected only by certain sensitive
instruments. (page 568)
Physical Science
The Nature of Light
Electromagnetic Spectrum
Physical Science
The Nature of Light
Electromagnetic Spectrum
Physical Science
The Nature of Light
The visible rays of the spectrum are
recognized by the human eye as color. In
order, these colors are red, orange,
yellow, green, blue, indigo (deep blue),
and violet. The shortest wavelengths that
we can see are those we call violet; the
longest ones are those we call red. (page
568)
Physical Science
The Nature of Light
Two theories about the nature of light
exist: the wave theory and the particle
theory. These theories seem to oppose
each other but really just focus on
different properties of light. According to
the Wave Theory of Light, light is a
luminous energy emitted by a light source
and travels through space as a transverse
wave. (page 568)
Physical Science
The Nature of Light
According to the Particle Theory of Light,
light energy is both radiated (transmitted)
and absorbed as tiny packets, or bundles,
and not as continuous waves. Atoms and
molecules are able to emit or absorb light
energy in specific amounts. (page 568)
Physical Science
EXERCISE 10
The Photoelectric Principle
Directions: Read the passage below and
answer the question that follows.
The electric eye, or photoelectric cell, is a
mechanism used to open and close a
garage door when a beam of light is
activated or broken. The principle of the
electric eye is based on the photoelectric
effect. (page 569)
Physical Science
EXERCISE 10
The Photoelectric Principle
The photoelectric effect occurs when a
beam of light strikes certain metals,
causing electrons to be knocked out of the
metal, producing an electric current. This
is how it happens: (page 569)
Physical Science
EXERCISE 10
The Photoelectric Principle
Light falling on the inside of a bulb coated
with an active substance causes electrons to
be emitted. The electrons are attracted to a
positively charged electrode positioned in
the center of the bulb as a filament. An
electric current results when the electrons
(negatively charged particles) are attracted
to the positively charged particles of the
electrode. (page 569)
Physical Science
EXERCISE 10
The Photoelectric Principle
It is observed that electrons are knocked loose
only when a certain light energy is reached.
The current can then be controlled by changes
in light intensity. It appears that electrons are
able to absorb only a certain amount of light at
one time. When light shines on the electric eye,
a current is established and the door moves.
When the beam of light is broken, the door
stops. (page 569)
Physical Science
EXERCISE 10
The Photoelectric Principle (page 569)
How does the principle of the electric eye act?
(1) to support the wave theory of light that light comes only
from a luminous source
(2) to dispute the belief that all light exists only as a
continuous wave
(3) to support the particle theory of light, which states that
light energy is transmitted in packets and bundles and not
as waves
(4) to complement the idea that light acts like particles in a
wave
(5) to contradict the idea that light is generated only in a star
Physical Science
PROPERTIES OF LIGHT WAVES (page 570)
Reflection -the angular return of a light wave
that occurs when it strikes a shiny surface
Example: light bouncing off a mirror
Refraction - the apparent bending of light
waves as they pass from one medium to
another
Example: drinking straw looking broken in a
glass of water
Physical Science
PROPERTIES OF LIGHT WAVES (page
570)
Diffraction - the bending of light waves
according to their wavelengths as they
pass near the edge of an obstacle or
through a small opening
Example: "rainbow" pattern on an old
phonograph record held edgewise toward
white light
Physical Science
PROPERTIES OF LIGHT WAVES (page
570)
Interference the altering of
brightness of light rays that occurs when
they interfere with each other, causing
reinforcement and cancellation
Example: holding thumb and finger
together and looking through the opening
at a bright light
Physical Science
PROPERTIES OF LIGHT WAVES (page
570)
Polarization - the restriction of light
waves to a particular plane, horizontal or
vertical
Example: sunglasses that minimize glare
off shiny surfaces
Physical Science
EXERCISE 11
Properties of Light Waves (page 570)
Directions: Use the information above to choose the best
answer for each question below.
1. A coin lying at the bottom of a pool is located at a
different point from where the eye perceives it to be. The
light rays from the coin bend as they pass from water to
air. This demonstrates
(1)
reflection
(2)
refraction
(3)
diffraction
(4)
interference
(5)
polarization
Physical Science
EXERCISE 11
Properties of Light Waves (page 570)
2. Rays of light striking a polished piece of
chrome appear to bounce off its surface.
This demonstrates
(1) reflection
(2) refraction
(3) diffraction
(4) interference
(5) polarization
Physical Science
The Nature of Electricity
Electricity is another invisible but vital
form of energy that we often take for
granted. Without electricity, however, our
lives would be paralyzed. The more
urbanized we become, the more
dependent on electricity we are. Nuclear
energy, despite its potential hazards, is an
important source for generating the
electrical power we need. (page 571)
Physical Science
The Nature of Electricity
Physicists define electricity as a form of
energy that results from the flow of loose
electrons— electrons weakly bound to
atoms. Electricity is closely related to
magnetism; therefore, the attractive force
of magnetism must be discussed in order
to explain electrical energy. (page 571)
Physical Science
The Nature of Electricity
Magnetism and Electrical Charges
The points of attraction at opposite ends of a
magnet are called its poles. Magnets have a
north and a south pole, also called a positive
and a negative pole. The opposite poles of
two magnets (a north pole and a south pole)
will attract each other. Correspondingly,
similar poles (two north or south poles) will
repel each other. (page 571)
Physical Science
The Nature of Electricity
Magnetism and Electrical Charges
The space around magnets is called a
magnetic field. Only a few natural and
synthetic materials can be magnetized—
iron, steel, nickel, cobalt, and some alloys.
A magnet, with its poles and lines of force,
is illustrated below. (page 571)
Physical Science
The Nature of Electricity
Magnetism and Electrical Charges
Physical Science
The Nature of Electricity
Magnetism and Electrical Charges
Physical Science
The Nature of Electricity
Magnetic Lines of Force
Every magnetic substance contains
domains, groups of molecules with attractive
forces. Before a substance is magnetized,
these domains are arranged randomly so
that the field of one domain is canceled out
by the field of another. When the substance
is magnetized, the domains line up parallel
to the lines of force, with all north poles
facing in the same direction. (page 571)
Physical Science
The Nature of Electricity
Magnetic Lines of Force
This arrangement makes a permanent
magnet out of a material in which the
domains are too weak to disarrange
themselves.
In most elements the atoms possess a
slight magnetic field because of their
spinning electrons. (page 571)
Physical Science
The Nature of Electricity
Magnetic Lines of Force
However, the fields cancel each other out
because the atoms rotate and spin in
different directions. In a magnet, however,
whole groups of atoms line up in one
direction and increase one another's
magnetic effect rather than cancel it out.
These magnetic concentrations are
magnetic domains. (page 571)
Physical Science
The Nature of Electricity
Static Electricity and Magnetism
Static electricity is a stationary electrical
charge caused by the friction of two
objects, one positively charged and the
other negatively charged. Static electricity
operates on the same principle as
magnetism. The rubbing of the carpet by
your shoes causes your body to become
electrified. (page 572)
Physical Science
The Nature of Electricity
Static Electricity and Magnetism
The shock you feel is caused by your
negatively charged body being neutralized
by the positive charge of the object you
touch. Upon contact your body is no longer
charged. Static electricity is stored and does
not move. The charged object must be
brought into contact with another object that
has an opposite charge for electrical shock
to occur. (page 572)
Physical Science
The Nature of Electricity
Static Electricity and Magnetism
Physical Science
EXERCISE 12
GED PRACTICE
Electricity and Magnetism
Directions: Choose the best answer for
the questions on page 573, The first
question is based on the following
paragraph.
Physical Science
EXERCISE 12
Electricity and Magnetism
Earth itself is surrounded by a magnetic
field. This may be because of strong electric
currents in Earth's core and the rotation of
Earth. The north magnetic pole is located in
Canada; the south magnetic pole is in nearly
the opposite location. The strong magnetic
attraction of these poles tends to align the
needle of a compass in a northerly-southerly
direction. (page 572)
Physical Science
EXERCISE 12
Electricity and Magnetism (page 573)
1. What makes a compass tell direction?
(1) The whole Earth acts as a magnet.
(2) The Chinese discovered the magnetic
poles.
(3) The Greeks discovered the magnetic poles.
(4) Large iron deposits are located in Canada.
(5) The magnetic attraction of Earth is
increasing.
Physical Science
EXERCISE 12
Electricity and Magnetism (page 573)
2. Which of the following would be
attracted to either pole of a magnet?
(1) a piece of aluminum
(2) a piece of brass
(3) a piece of tin
(4) an unmagnetized piece of cobalt
(5) a magnetized piece of cobalt
Physical Science
Electric Currents
Early scientists who experimented with
electric charges found that charges could
move easily through certain materials called
conductors. As you learned in the chemistry
section, metal was found to be a good
conductor of electricity, as were salt
solutions, acids, and hot gases. Other
materials such as rubber were found not to
conduct charges at all. These materials are
called insulators. (page 573)
Physical Science
Electric Currents
An electric current is created by an electric
charge in motion. In a solid conductor, such
as wire, the current is a stream of moving
electrons. In a liquid or gas, the current may
be positively and negatively charged
atoms— ions. An electric current flowing
through a solid conductor can be compared
to the flow of water through the pipes in your
plumbing system. (page 573)
Physical Science
Electric Currents
An electric current moves slowly—about a
hundredth of an inch per second.
Although our lights come on instantly
when a switch is turned on, it is because
the wires are always filled with electrons,
just as a water pipe is always filled with
water. (page 573)
Physical Science
Electromagnets
An electromagnet is a core of soft magnetic
material surrounded by a coil of wire. An
electric current is passed through the wire to
magnetize the core when a switch is flicked
or a button is pushed. The device then has
the power to attract iron objects. When the
switch is turned off, the attraction is broken.
Electromagnets are used in radios and in
ordinary doorbells. (page 573)
Physical Science
EXERCISE 13 (page 575)
Conductors and Insulators
Directions: Identify the following terms as
either a conductor of electricity (C) or an
insulator (I).
1. ________ leather
2. ________ wood
3. ________ salt water
4. ________ plastic
5. ________ copper
Physical Science
EXERCISE 14 (page 574)
Electromagnets
Directions: Choose the best answer for the following
questions.
1. Why would a radio with a strong electromagnet be placed
far away from the navigation instruments on a plane or ship?
(1) The radio wouldn't work because of electrical interference.
(2) The radio couldn't be heard clearly because of static.
(3) The accuracy of the compass would be affected by the
magnetic field established by the radio's electromagnet.
(4) The radio's electromagnet would cause all the navigation
instruments to malfunction.
(5) The radio would draw too much electrical energy, causing
the electrical system of the ship or plane to discharge.
Physical Science
EXERCISE 14 (page 574)
Electromagnets
2. Identify which of the following are true
(T) or false (F).
___ You need an insulator to keep
electricity flowing only along wires.
___ Electromagnets are used in doorbells.
___ When the switch is in the off position,
electricity still is flowing through the
circuit.
Physical Science
Creating Electricity
Electricity is created by power companies
and sent to our homes by high voltage
wires through transformers. There are
several ways to create electricity. Because
there is a concern about the limited
quantities of fossil fuels, alternative power
supplies for electricity are being used.
(page 575)
Physical Science
Creating Electricity
One system requires the fission of nuclear
energy in nuclear power plants. These
plants bombard the nuclei of large
unstable uranium atoms with neutrons.
The large release of heat is used to heat
water, which is used to turn a turbine, a
wire loop connecting two magnets. (page
575)
Physical Science
Creating Electricity
When the turbine is forced to turn, the
electrons are stolen from the magnets and
sent through the wire as electricity. This
alternative energy has many drawbacks,
including the safe disposal of radioactive
nuclear waste left over from the reaction.
(page 575)
Physical Science
Creating Electricity
TURBINE
Physical Science
Creating Electricity
TURBINE
Physical Science
Creating Electricity
TURBINE
Physical Science
Creating Electricity
Another alternative is solar energy. Scientists
have found that pure silicon (found in sand and
one of the most common elements in the crust
of the Earth) is electrically excited in the
presence of light. You may have experienced
this if you own a solar calculator, but it may not
have performed in a dimly lighted area. The
sun's energy excites the electrons, which then
flow along wires to provide electricity to the
attached appliance. (page 575)
Physical Science
Creating Electricity
SOLAR ENERGY
Physical Science
Creating Electricity
SOLAR ENERGY
Physical Science
Creating Electricity
SOLAR ENERGY
Physical Science
Creating Electricity
Other alternative energies are limited to
the availability of the conditions necessary
to generate electricity. One such
alternative is wind power, which has been
successfully captured through the use of
windmills throughout the history of
civilization. California has wind farms
where many large windmills are connected
to generate electricity. (page 576)
Physical Science
Creating Electricity
These new models on the old design limit
the number of arms on the mill and make
these arms out of durable synthetic
materials. Windmills do not need a strong
wind; in fact, strong winds can damage
the mechanics. The best condition is a
steady wind that maintains a continuous
motion of the flywheel. (page 576)
Physical Science
Creating Electricity
WIND ENERGY
Physical Science
Creating Electricity
WIND ENERGY
Physical Science
Creating Electricity
WIND ENERGY
Physical Science
Creating Electricity
WIND ENERGY
Physical Science
Creating Electricity
Hydroelectric power is another source
that has to be limited to the already
established use of the water flow in the
region. Many rivers are used as
transportation and cannot be dammed to
provide the reservoir of water needed to
control the flow of water through the
turbine system. (page 576)
Physical Science
Creating Electricity
Yet hydroelectric power, as well as wind
and solar powers is a clean, renewable
resource. Critics suggest that the reason
these systems have not been fully
developed is the fear energy companies
have in reducing their own incomes.
(page 576)
Physical Science
Creating Electricity
Hydroelectric power
Physical Science
Creating Electricity
Hydroelectric power
Physical Science
Creating Electricity
Hydroelectric power
Physical Science
EXERCISE 15
Creating Electricity (page 577)
Directions: Use the information above to fill in the blanks in
each statement below.
1. Hydroelectric power is not always possible because
sometimes rivers are used for _______________.
2. Fossil fuels will not be around forever, so we need to
explore the use of other energy systems called
_______________.
3. Windmills do not need strong wind, but they do need
_______________ wind.
4. Pure silicon has electrons that are excited into motion by
_________________.
5. A loop or wire that is turned between two magnets and
creates electricity is a _______________.