Download Chapter 2: Science and the Universe

2. Science and the Universe
and the ideas it supports (or does not support). In doing
so, you will gain experience in using the scientific
method as you learn about our modern understanding of
our surroundings.
The task of physical science is to describe the entire
universe, from its tiniest components to its largest collections of matter, living and nonliving, and to understand the rules governing its behavior. To begin, we
will sketch a description of the universe and show how
the universe is constructed from a few simple components. You may think of this description as a kind of
map of the material we will discuss in this book. Each
step in the description will be elaborated in subsequent
chapters, where we will elaborate each level of description, explain the rules governing the changes that occur,
and present some of the relevant evidence.
Humans have always been curious about their environment and how they relate to and control it.
Earthquakes, volcanoes, hurricanes, and drought are
examples of natural phenomena that have affected lives
in important ways. People have sought to control these
phenomena, or at least their impact on human lives.
Over the years people have built “models” or “schema”
of how natural phenomena worked. In earlier times
these models often claimed a supernatural relationship
among humans, gods, and natural phenomena. Our
models of the physical world today have evolved
significantly from those of our ancestors of just a few
generations ago.
Whatever the motivation, we now know more
about the universe than our ancestors did. Their curiosity and study helped unveil a structure and order that is
more profound, yet simpler, than they could have imagined. We truly do live in the age of science. Our lives
are partly controlled and greatly enriched by the fruits
of our knowledge, and science gives us the power to
continue improving the conditions under which we live.
Those who have little control over their society
might argue that they need not pay attention to the
knowledge and ideas of science. However, in a free
society, citizens are often able to make decisions about
the interaction of science and their lives. Wrong choices might unleash a destructive mechanism or might
deny them the use of a technology that could be the
basis of future prosperity and peace. The freedom to
choose implies the responsibility to understand. If we
use our knowledge unwisely, we have the power to
destroy our civilization.
Our purposes in this book are to describe the universe and the rules that govern it and to help you gain
some experience with the scientific method of thinking.
We will do this without using sophisticated mathematical notation even though the description is more elegant
in that form. We cannot describe every detail in a book
of this size, so we have chosen those parts of the universe that seem to us most interesting and important and
those rules or laws that have the broadest range of application. Further, we will explain some of the evidence
that leads us to believe that what we describe is valid.
You will gain the most from your study if you make sure
you understand the relationship between the evidence
The World Around Us
As we go through life we encounter a dazzling
array of objects and materials. Bricks, rocks, sand,
glass, soil, air, cans, footballs, rain, mountains, trees,
dogs, and many other things are forms of matter that
enrich our lives. And there is motion all around. Rain
falls, rivers flow, the wind blows, cars and people start
and stop, waves move across a lake, objects fall to the
ground, smoke rises, the sun and stars move through the
heavens, and the grass grows. Matter also seems to
change form in arbitrary ways. Wood burns and disappears, whereas water does not burn but may disappear
all the same.
This variety in motion and matter at first seems
unfathomable. How can mere humans, so limited in
senses and mobility, hope to comprehend it all? Can
any order exist in such diversity? Are there rules which
govern change?
The answers have come through the centuries, little
by little. Gifted and persistent people have learned to
ask the right questions and how to induce nature to yield
the answers. Each stands upon the shoulders of those
who went before and thereby gains a more complete
view. We together stand at the apex of a great pyramid
of giants from which we view the truth more completely than people in any other age.
What we see is astounding. Much of the physical
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Some objects have a characteristic called electric
charge. Charge may be positive or negative and is a
characteristic associated specifically with the electromagnetic force. Objects with like charges are repelled
by the electromagnetic force while objects with opposite charges attract one another. Objects may also have
a characteristic called mass. Objects with mass are
attracted (never repelled) by the force of gravity.
world can be understood simply. Matter is made up of
only a few kinds of pieces, which can be arranged in
countless ways. The motion we see around us depends
on just a few simple rules. Changes in form and substance are also easy to understand in terms of a few
comparatively simple ideas. When these rules and ideas
are understood, chaos becomes order. Order and law
really do govern our world. Even living things seem to
operate on the same principles. The laws of force and
motion and chemical change govern the processes of
life as well as the behavior of nonliving objects.
But the view is not yet complete. As we consider
our knowledge and observations, we encounter questions for which the answers are not yet known. Perhaps
we have not asked the right questions. Perhaps we are
just not yet wise enough to understand the answers. At
any rate, asking and trying to solve the puzzle is half the
fun. We will try to let you share the mysteries as well
as the answers as we proceed.
A distinctive nomenclature is worth noting. When
we speak of objects too small to be seen without a
microscope, we refer to them as microscopic objects.
Atoms, molecules, and their constituents are microscopic, as are most living cells. Objects large enough to
be seen without the aid of a microscope are macroscopic. Thus, one way to characterize this chapter is to
say that we are describing the macroscopic parts of the
universe in terms of its microscopic constituents (a
strategy called reductionism). This, as you will see, is
the key to understanding the structure and behavior of
the universe in terms of a few simple ideas.
It is often useful in the study of physical objects to
categorize and compare them on the basis of their size
and the forces that hold them together. The size of a
physical object may be given in terms of its spatial
dimensions. People-sized objects have typical dimensions of a meter or a few meters or a fraction of a meter.
Much smaller objects, such as cells in the human body,
have typical dimensions of micrometers (millionths of a
meter). The extremely small nuclei of atoms typically
have dimensions of milli-micro-micrometers (thousandth-millionth-millionths of a meter). Buildings have
dimensions of a few tens to a few hundreds of meters.
The earth is approximately spherical in shape with a
diameter of about 13,000 kilometers. The earth moves
about the sun in an approximately circular orbit with a
diameter of about 300 million kilometers. The Milky
Way has a diameter of about 100,000 light years. (A light
year is approximately 10 million million kilometers.)
There are four basic forces in nature: strong force,
electromagnetic force, weak force, and gravity. In
some structures these four forces may be at work simultaneously and may even have opposite effects. The
strong force is operative only over very short distances
while the electromagnetic force and gravity, in contrast,
reach much further, although they weaken with distance.
Nuclear Matter
All matter as we currently understand it is made up
of elementary particles, point-like objects without size
or structure. Among these particles we number quarks
and electrons. The electron carries a unit of negative
electric charge. Quarks are charged particles, each carrying a positive or negative charge equal to one-third or
two-thirds the charge of a single electron.
Structures called nucleons consist of three quarks
bound together by the strong force. Positively charged
nucleons (called protons) are made of two quarks with
charge !2/3 and one with charge "1/3. Neutral nucleons (called neutrons) have one quark with charge
!2/3 and two with charge "1/3, adding together to
yield zero net charge.
Nucleons are so small that it would take one million million (or 1012) lined up next to each other to reach
across the head of a pin. (We will use the notation 1012
[spoken “ten to the twelfth”], because it is an easy way
to keep track of the zeros in large or small numbers. By
1012 we mean that we start with 1.0 and move the decimal 12 spaces to the right, resulting in the number
1,000,000,000,000. On the other hand, 10–12 would
mean that the decimal point is moved 12 spaces to the
Figure 2.1. Models of atomic nuclei: (a) helium, (b)
oxygen, (c) uranium.
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left, resulting in the number 0.000,000,000,001.)
Nucleons are so dense, however, that a pinhead-size ball
made of nucleons packed next to each other would
weigh about a million tons. No crane could lift it.
Nucleons coalesce into incredibly small lumps containing from 1 to 238 nucleons, half or more of which are
neutrons and the rest protons. Each of these tiny aggregates is the nucleus of an atom (Fig. 2.1). Larger collections of nucleons have been formed in laboratories,
but these always break up quickly into smaller groups.
The strong force also holds the protons and neutrons in the nucleus of an atom together. Nucleons
attract each other (that is, protons attract other protons
as well as neutrons; neutrons do the same) by means of
the strong force. This means the strong force must overwhelm the electromagnetic repulsion of the positively
charged protons. (The electromagnetic force holds
atoms, molecules, and people-sized objects together
where the separations exceed the range of the strong
force.) The strong force is responsible for the energy
released by the sun, nuclear reactors, and nuclear explosives. The weak force is also involved in the nucleus
but does not control any of the common structures.
Some of the nuclei found in nature are unstable.
These spontaneously emit high-speed particles. Such
nuclei are called radioactive.
There is normally one electron in the atom for each proton in a nucleus, so that the atom is electrically neutral.
Neutrons are in atomic nuclei as well, but the number may
vary for atoms that are otherwise identical.
Compared with its nucleus, an atom is enormous.
If you imagine the nucleus to have a diameter the size
of a ballpoint pen tip, the atom would have a diameter
equal to the length of a football field (Fig. 2.2). An
atom is mostly empty space. In some ways the nucleus
is like a small gnat in the center of a large building. The
walls and ceiling of the building and all the space inside
are patrolled by the electrons, which move rapidly about
like a swarm of bees protecting the atom from intruders.
Atoms are 100,000 times as large as their nuclei,
but they are still so small that 5 million are needed to
form a line across the smallest dot. The electrons have
little mass (about 1/1,836 that of nucleons), so atoms
have about the same mass as their nuclei. A pinheadsize ball of atoms has about 1021 atoms and weighs
about as much as a pinhead.
Although individual atoms are much too small to see,
you are undoubtedly familiar with objects composed of
large groups of essentially identical atoms. For instance,
a copper penny is made of approximately 30 billion trillion (3 # 1022) copper atoms. A material like copper
composed of only one type of atom is called an element.
Additional examples are iron, helium, and uranium.
Atoms
Molecules and Crystals
Each atomic nucleus carries a positive electric charge
and attracts a certain number of negatively charged electrons. The nucleus and electrons together form an atom.
Atoms, in a variety of combinations, make up matter as we know it. The tiniest speck of dust visible to the
unaided eye contains about 1018 atoms. A sample of air
the size of a sugar cube has about the same number.
Certain atoms join together in small groups by
sharing electrons in a way that takes advantage of electromagnetic interactions. Such a group of atoms is
called a molecule. Molecules are the basis of many of
the common materials you see around you. Sugar is
composed of molecules, each containing 12 carbon
atoms, 22 hydrogen atoms, and 11 oxygen atoms. Many
molecules contain fewer than 50 atoms, although polymers like nylon are long chains that may contain a million or more. A molecule of the common fuel butane is
shown in Figure 2.3.
Figure 2.3. A butane molecule (carbon atoms are shown
in black, hydrogen in white).
Figure 2.2. An atom is mostly empty space. On this scale,
the nucleus is still only the size of a ballpoint pen tip.
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Molecules do not deteriorate easily, as your experience with sugar will tell you. Sugar does not spontaneously change into some other material. Yet many
common processes can tear molecules apart and
reassemble them in different ways. For instance, sugar
can be burned. It can also be digested to release its
stored energy for use in muscles. This stored chemical
energy (based on electromagnetic forces) has been
mankind’s most common source of energy.
Atoms attract each other, because the protons in
each atom and the electrons in its neighbors are attracted to each other by the electromagnetic interaction.
Adjacent atoms do not get too close, however, because
the positively charged protons in each atom repel the
protons in the other. The strong force is inoperative at
these distances. Electrons also repel each other. The
net result of these electrical attractions and repulsions is
the force that holds atoms together. We feel this force
when, for example, we tear a piece of paper (separating
some of its atoms from each other), bend a piece of
metal, strike our head against a solid object, or walk
across a room. In fact, these interatomic electric forces
are involved in almost everything we do and are responsible for almost all the forces we experience directly.
Most common materials contain several kinds of
molecules. Milk has over a hundred kinds of molecules
and the human body has somewhere near 50,000. The
task of identifying important molecules and studying
their properties has been one of the great challenges of
modern chemistry and biology.
Some materials are just large numbers of identical
atoms or molecules piled on top of one another. In liquids these slide around each other much like small ball
bearings or buckshot in an open can. In solids the atoms
sometimes arrange themselves in an orderly array called
a crystal. For example, common table salt is a collection
of equal numbers of sodium and chlorine atoms in a cubical arrangement. Many solid materials are collections of
small crystals held together by the electrical force. The
type of atomic organization in crystals generally determines the properties of the bulk material. Carbon atoms,
for example, can be arranged in two different ways—one
forms diamond; the other, graphite (the “lead” in a pencil). Diamond is clear, colorless, and hard; graphite is
opaque, black, and soft. Yet both are composed of the
same kind of atoms. Color Plate 1 (located in the color
photo section near the end of the book) shows regularly
ordered carbon atoms in graphite as imaged with a scanning tunneling microscope. Color Plate 2 shows regularly spaced sulfur atoms in molybdenum disulfide as
imaged with a scanning tunneling microscope.
es of molecules. Our bodies are composed of various
bony and tissue structures which are very large integrated collections of complex molecules. The living plants
and animals around us share similar molecular complexes in their structure.
The fuel we burn may be composed of homogeneous collections of molecules, as in natural gas, or heterogeneous collections of molecules, as in wood.
Buildings are made of steel and concrete and glass;
vehicles of metal and plastic. Each in turn is composed
of molecular complexes.
The Earth
The earth on which we live is a huge ball with a
radius of almost 6400 kilometers (4000 miles). It is so
large that we generally perceive it to be flat from our
perch upon its surface. We do not generally notice that
the surface of a lake curves downward so that it is about
30 feet higher at our feet than it is 5 miles away.
Nevertheless, pictures taken from space reveal the overall spherical shape, a shape which has been known indirectly for centuries.
The outer layer, or crust, is a comparatively thin
skin composed of a variety of rocks and materials. The
mountains, which seem so magnificent and overpowering to us, are no more than the smallest wrinkles when
compared with the earth as a whole—thinner, by comparison, than the skin on an apple.
We may think of the whole earth as being the same
as the crust we experience. But the crust is not at all
representative of the interior (Fig. 2.4). The core of the
earth is thought to be a hot (3500 °C or more) ball of
iron and nickel under tremendous pressure. The core
seems to have two parts: a solid inner core and an outer
core. The latter has many properties normally associated with liquids. The core constitutes about 30 percent
of the earth’s volume and one-half its mass.
Inner Core
Mantle
Outer Core
Complexes of Molecules
Some physical objects that we have firsthand
experience with are composed of one or more complex-
Figure 2.4. The internal structure of the earth.
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Surrounding the core is the mantle, a 2900-kilometer-thick layer of solid rock that constitutes most of
the earth. The mantle is composed almost entirely of
rocks made of the elements silicon, oxygen, magnesium, and iron. Evidence indicates that its temperature ranges from 2700 °C just outside the core to 1000
°C just inside the crust.
The rigid outer layer of the earth is divided into
several sections, or plates, upon which the continents
rest. These plates move slowly over the surface of the
earth, sometimes colliding with each other with enormous force and sometimes separating to leave a rift
through which molten rock from lower levels may
escape onto the ocean floor. Many of the phenomena
we observe (e.g., earthquakes, volcanic activity, and
mountain building) can be understood in terms of the
motion of these plates. Their discovery and study, a
field of inquiry known as plate tectonics, has been one
of the major triumphs of modern geology.
The gravitational and electromagnetic forces combine to govern the size of the earth. Each piece of the
earth is attracted to every other piece by gravity, the
result being a net force directed toward the center of the
earth. As the atoms that make up the earth are pulled
close together by gravity, their interatomic (electromagnetic) forces begin to resist. Otherwise, the earth would
collapse into a much smaller ball. The nuclear force
also plays an important role in the earth’s dynamics,
releasing energy from radioactive nuclei that keeps the
interior of the earth hot.
Neptune, and Pluto. Pluto, usually the outermost, travels in an elliptical orbit that varies from 4 to 5.5 billion
kilometers from the sun and sometimes carries the planet inside the orbit of Neptune. Again, the scale is hard
to comprehend. If we were to start today and travel with
a constant speed of 40,000 kilometers/hour, about as
fast as the fastest rocket, it would take about 14 years to
reach Pluto.
The planets differ in their speeds as they travel
around the sun. Mercury, the fastest at a speed of
170,000 kilometers/hour (110,000 miles/hour), completes its orbit in just 88 days. Pluto, the slowest, travels only one-tenth as fast and takes almost 250 years to
complete its orbit. The earth’s orbital speed is a moderate 107,000 kilometers/hour (67,000 miles/hour).
The sun governs these motions through the gravitational force that reaches out through the immensity of
space to hold the planets in their orbits. The sun itself
is a vast collection of atomic nuclei, mostly hydrogen,
and electrons. These charged particles are free to move
about independently of one another in a kind of gaseous
state called a plasma. (Over 99 percent of all visible
matter in the universe is in the plasma state.) The temperature of the sun is quite high, ranging from about 15
million degrees Celsius at the center to about 5500 °C
near its surface. The nuclear furnaces of the sun provide
the light that illuminates its satellites. This light is the
principal source of terrestrial energy, providing the
energy for atmospheric motion, for plant and animal
growth, and for virtually every process that occurs on
the planetary surface.
The Solar System
The Milky Way Galaxy and Beyond
Circling the sun with the earth are eight other planets (with their moons), several comets, and a variety of
smaller objects called asteroids. Together these bodies
form the solar system (Fig. 2.5). The nine planets are
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus,
The sun is just one of the billions of stars, a few of
which can be seen on any clear night, particularly if
interference from artificial lighting is not too great.
Those closest to us form the Milky Way galaxy (Color
Plate 3, see color photo section near the end of the
book), an immense collection of 100 billion stars held
together by their mutual gravitational attractions. The
stars of the Milky Way are, on the average, about 30 trillion miles apart, a distance so great that it takes light six
years to traverse it. The distance that light can travel in
a year is called a light-year. The galaxy itself is
600,000 trillion miles across; it requires 100,000 years
for light to go from one side to the other, so the diameter of the galaxy is about 100,000 light-years. If the universe were to shrink so that the sun was reduced to the
size of an orange, the stars in the galaxy would be about
1,000 miles from their nearest neighbors and the galaxy
as a whole would be 20 million miles across.
The picture is still not complete. Millions of galaxies have been seen through our most powerful telescopes. Each contains billions of stars. Some galaxies
are grouped together in clusters, with individual clusters
Figure 2.5. The solar system.
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containing as many as 10,000 galaxies. Our Milky Way
is part of a smaller cluster, called the Local Group,
which contains one other spiral galaxy and several
fainter objects. The typical distance between galaxies
in a cluster is a million light years.
With all this, keep in mind that the universe is
mostly empty space. The stars and galaxies, although
immense from our perspective, are mere specks when
compared to the immensity of the universe in which
they move. The space between them is emptier than the
most perfect vacuum attainable on the earth.
?
Universe
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10
Clusters of Galaxies
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10
20
10
Galaxies
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10
10
Distance to nearest stars
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Summary
Gravity
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By now you might feel a little unstable. Think of
the range of things we have described—from nucleons
so tiny that a quadrillion of them could fit in a line
across a small pinhead, to clusters of galaxies so vast
that even light takes many millions of years to go from
one side to the other. As the structure is built up level
by level, perhaps you can see that each level of organization is a logical combination of simpler ones.
Try not to be overwhelmed by all the numbers and
names. The important names will recur in subsequent
chapters so that you will become familiar with them as
we proceed. The short exercises at the end of this chapter will help you to put things into proper perspective.
The purpose of this chapter is to help you develop an
accurate framework into which you can fit the more complete and precise information that follows (Fig. 2.6).
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Solar System
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10
10
8
10
6
10
4
10
2
10
0
Planets
Continents
Mountains
Historical Perspectives
Plants, Animals, People
-2
10
-4
10
10
One-celled organisms, bacteria
-6
-8
10
10
-10
10
-12
-16
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Molecules
Atoms
Nucleus
Protons, Neutrons
Quarks
?
Strong Force
-14
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Viruses
Science as practiced today has evolved over five or
so millennia. Some early roots of science may have
appeared as early as 3000 B.C. in observations of the
heavens. The Babylonians developed the “art” of astrology from their observations and charting of lunar cycles
and the apparent motions of the sun and planets. The
Egyptians had a rather sophisticated understanding of the
seasonal cycles, probably motivated by their need to predict the yearly overflow of the Nile. At Stonehenge in
England stones were arranged so as to predict the
eclipses. In these civilizations the apparent motion of the
sun and the planets played an important role.
The Greek civilization produced many philosophers who pondered nature and described its workings.
As we have already noted, Pythagoras (ca. 550 B.C.)
introduced the notion of a spherical earth and a spherical universe. Democritus (ca. 450 B.C.) introduced the
notion of the atom as the smallest particle into which
matter could be divided. Aristotle (ca. 350 B.C.) envisioned a universe consisting of a spherical earth surrounded by spherical shells containing the planets and
stars. Aristotle taught the young Alexander who
became Alexander the Great and who established a city
Electromagnetic Force
Size [in meters]
10
Stars
Figure 2.6. The sizes of things. How much larger than
10n is 10n+1?
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and center of learning at Alexandria, Egypt.
Archimedes (ca. 250 B.C.) and Ptolemy (ca. A.D. 150)
were two of many important pupils of the Alexandrian
Academy.
The Ptolemaic model of the universe had a spherical earth at rest at its center. The planetary motions
were explained in terms of epicycles—one circular
motion about a point which in turn moved in a circular
motion about some other point.
When Islamic forces conquered Alexandria (ca.
A.D. 500) there was a flow of scientific information to
the East. Baghdad became a center for the exchange of
knowledge, and many works were translated into
Arabic. Much of the body of scientific knowledge was
preserved and enlarged in nations under Islamic influence. Many Greek ideas were preserved during this
period at Constantinople, which was not conquered by
Islamic forces until the 15th century.
The Dark Ages encompassed Europe until about
the 15th century, when the Renaissance developed. As
the Greeks lost Constantinople they fled into Europe
and carried with them their scientific and cultural treasures. At this time the Moorish influence in southern
Spain also provided an infusion into Europe of the science preserved by the Islamic culture.
In England, Francis Bacon (1561-1626) introduced the inductive method, in which observations of
many specific cases are generalized as the laws of
nature. In contrast, the deductive method employs general assumptions (which may or may not be true) from
which specific conclusions are logically deduced.
C. GLOSSARY
1. Atom: A structure made up of a nucleus (containing protons and neutrons) and surrounding electrons. The electrons are bound to the nucleus by the
electromagnetic force.
2. Core: The spherical center of the earth. The solid
inner core consists of iron and nickel while the liquid outer core surrounds the inner core and consists
of molten iron and nickel.
3. Crust: The relatively thin outer layer of rock that
forms the surface of the earth.
4. Crystal: A form of solid in which atoms or molecules arrange themselves in orderly arrays to create
distinctive geometric shapes. Common table salt
exists as crystals.
5. Electric Charge: A characteristic of objects that
determines the strength of their electromagnetic
interaction (force) with matter, specifically with
other charged objects.
6. Electron: A particular kind of elementary particle
that carries a negative charge, has an electromagnetic interaction with matter, and is a constituent
part of atoms. Electrons are best represented as a
point without spatial extent.
7. Element: A substance made up of atoms, all of
which contain the same number of protons.
Hydrogen, helium, silver and gold are elements.
8. Light-Year: The distance light can travel in one
year, i.e., about 6 trillion miles.
9. Macroscopic: A descriptive adjective referring to
the sizes of objects large enough to see with the
unaided eye. Automobiles and basketballs are
macroscopic objects.
10. Mantle: The spherical shell of rock that lies under
the crust of the earth but overlies its core.
11. Mass: A characteristic of objects that determines
the degree to which they can be accelerated by
applied forces. Mass is also a characteristic of
objects that determines the strength of their gravitational interaction with matter, specifically with
other objects with mass.
12. Microscopic: A descriptive adjective referring to
the sizes of objects at the limit of visibility with the
unaided eye or smaller. Molecules and atoms are
described as microscopic objects.
13. Molecule: A microscopic structure usually made up
of more than one atom.
14. Neutrino: A particular kind of elementary particle
that carries no electrical charge, is best represented
by a point without spatial extent, and is particularly
notable for having neither a strong nor an electromagnetic interaction with matter. The neutrino
interacts with matter through the fundamental force
called the “weak force.”
15. Neutron: A composite, strongly-interacting particle made up of three quarks, but which carries no
STUDY GUIDE
Chapter 2: Science and the Universe
A. FUNDAMENTAL PRINCIPLES
1. The Strong Interaction: The interaction between
objects that gives rise to one of four fundamental
forces in nature, called the “strong force.” The
strong force is a short-range, nuclear force which is
responsible for the binding of the nucleus together
as a structure.
2. The Electromagnetic Interaction: The interaction between objects that gives rise to the electrical
(or, better, the electromagnetic) force. The electromagnetic force is also fundamental and is responsible for binding atoms and molecules as structures.
3. The Gravitational Interaction: The interaction
between objects that gives rise to the weakest of the
fundamental forces, the gravitational force. The
gravitational force is responsible for binding structures such as the solar system and galaxies.
B. MODELS, IDEAS, QUESTIONS, OR APPLICATIONS
None
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16.
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18.
19.
20.
21.
22.
23.
24.
net electrical charge. Neutrons are a constituent
part of the nucleus of atoms.
Nucleon: A generic name for either a proton or a
neutron.
Nucleus: The very small core structure at the center of an atom. The nucleus is a structure of protons
and neutrons held together by the strong force.
Plasma: A physical state of matter (such as solids,
liquids, and gases) that is characterized by fluid
properties, but in which particles with positive and
negative electric charges move independently.
Plates: Pieces or sections of the fractured rigid
outer layer of the earth on which the continents and
ocean basins sit.
Proton: A composite, strongly interacting particle
made up of three quarks. The proton carries a positive electrical charge and is a constituent part of the
nucleus of atoms.
Quarks: The elementary particles of which protons and neutrons consist. A proton and a neutron
each consist of three quarks.
Reductionism: A strategy of science to understand
complex structures by reducing them to their smaller and simpler parts.
Solar System: A star with its associated revolving
planets, moons, asteroids, comets, etc.
Weak Force: One of four fundamental forces of
nature (strong, electromagnetic, weak and gravity).
Unlike the other three, the weak force is not directly associated with binding together the common
structures of the universe.
2.2. By analogy or number, contrast the size of the
nucleus and the size of the atom.
2.3. By analogy or number, contrast the distances
between stars, the size of the galaxy, and the distance
between galaxies.
2.4. Describe the organization of the universe.
Show how clusters of galaxies are ultimately composed
of the simplest entities we know about.
2.5. Is it true that matter is “mostly empty space”?
Explain what this statement means by describing the
real structure of
(a) an atom
(b) a steel ball bearing
(c) a galaxy
2.6. Of the five levels of organization listed here,
which is second in order of increasing size and complexity?
(a) quark
(b) apple
(c) moon
(d) gold nucleus
(e) protein molecule
2.7. Which of the following forces is electrical?
(a) weight of a book
(b) force exerted by book on table
(c) gravitational force of earth
(d) force keeping the moon in orbit
(e) force keeping the solar system together
D. FOCUS QUESTIONS
1. Identify at least five levels of organization observed
in the universe. Describe these levels of organization
in order, beginning with the smallest, and explain
how each structure is held together. Identify the fundamental force which dominates in each structure.
E. EXERCISES
2.1. For each of the following structures, identify
their primary constituent parts and their sizes and the
fundamental force(s) which maintain the integrity of the
structure.
cluster of galaxies
galaxy
solar system
star
earth
crystal
molecule
atom
nucleus
nucleon
quark
electron
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