INTRODUCTION: THE NATURE OF SCIENCE AND
Figure 1.1Galaxies are as immense as atoms are small. Yet the same laws of physics describe both, and all the rest of nature—an indication of the underlying unity in the
universe. The laws of physics are surprisingly few in number, implying an underlying simplicity to nature’s apparent complexity. (credit: NASA, JPL-Caltech, P. Barmby,
Harvard-Smithsonian Center for Astrophysics)
1.1.Physics: An Introduction
• Explain the difference between a principle and a law.
• Explain the difference between a model and a theory.
1.2.Physical Quantities and Units
• Perform unit conversions both in the SI and English units.
• Explain the most common prefixes in the SI units and be able to write them in scientific notation.
1.3.Accuracy, Precision, and Significant Figures
• Determine the appropriate number of significant figures in both addition and subtraction, as well as multiplication and division
• Calculate the percent uncertainty of a measurement.
• Make reasonable approximations based on given data.
Introduction to Science and the Realm of Physics, Physical Quantities, and Units
What is your first reaction when you hear the word “physics”? Did you imagine working through difficult equations or memorizing formulas that seem
to have no real use in life outside the physics classroom? Many people come to the subject of physics with a bit of fear. But as you begin your
exploration of this broad-ranging subject, you may soon come to realize that physics plays a much larger role in your life than you first thought, no
matter your life goals or career choice.
For example, take a look at the image above. This image is of the Andromeda Galaxy, which contains billions of individual stars, huge clouds of gas,
and dust. Two smaller galaxies are also visible as bright blue spots in the background. At a staggering 2.5 million light years from the Earth, this
galaxy is the nearest one to our own galaxy (which is called the Milky Way). The stars and planets that make up Andromeda might seem to be the
furthest thing from most people’s regular, everyday lives. But Andromeda is a great starting point to think about the forces that hold together the
universe. The forces that cause Andromeda to act as it does are the same forces we contend with here on Earth, whether we are planning to send a
rocket into space or simply raise the walls for a new home. The same gravity that causes the stars of Andromeda to rotate and revolve also causes
water to flow over hydroelectric dams here on Earth. Tonight, take a moment to look up at the stars. The forces out there are the same as the ones
here on Earth. Through a study of physics, you may gain a greater understanding of the interconnectedness of everything we can see and know in
Think now about all of the technological devices that you use on a regular basis. Computers, smart phones, GPS systems, MP3 players, and satellite
radio might come to mind. Next, think about the most exciting modern technologies that you have heard about in the news, such as trains that levitate
above tracks, “invisibility cloaks” that bend light around them, and microscopic robots that fight cancer cells in our bodies. All of these groundbreaking
advancements, commonplace or unbelievable, rely on the principles of physics. Aside from playing a significant role in technology, professionals such
as engineers, pilots, physicians, physical therapists, electricians, and computer programmers apply physics concepts in their daily work. For example,
a pilot must understand how wind forces affect a flight path and a physical therapist must understand how the muscles in the body experience forces
as they move and bend. As you will learn in this text, physics principles are propelling new, exciting technologies, and these principles are applied in
a wide range of careers.
In this text, you will begin to explore the history of the formal study of physics, beginning with natural philosophy and the ancient Greeks, and leading
up through a review of Sir Isaac Newton and the laws of physics that bear his name. You will also be introduced to the standards scientists use when
they study physical quantities and the interrelated system of measurements most of the scientific community uses to communicate in a single
CHAPTER 1 | INTRODUCTION: THE NATURE OF SCIENCE AND PHYSICS S 11
mathematical language. Finally, you will study the limits of our ability to be accurate and precise, and the reasons scientists go to painstaking lengths
to be as clear as possible regarding their own limitations.
1.1Physics: An Introduction
Figure 1.2The flight formations of migratory birds such as Canada geese are governed by the laws of physics. (credit: David Merrett)
The physical universe is enormously complex in its detail. Every day, each of us observes a great variety of objects and phenomena. Over the
centuries, the curiosity of the human race has led us collectively to explore and catalog a tremendous wealth of information. From the flight of birds to
the colors of flowers, from lightning to gravity, from quarks to clusters of galaxies, from the flow of time to the mystery of the creation of the universe,
we have asked questions and assembled huge arrays of facts. In the face of all these details, we have discovered that a surprisingly small and
unified set of physical laws can explain what we observe. As humans, we make generalizations and seek order. We have found that nature is
remarkably cooperative—it exhibits theunderlying order and simplicitywe so value.
It is the underlying order of nature that makes science in general, and physics in particular, so enjoyable to study. For example, what do a bag of
chips and a car battery have in common? Both contain energy that can be converted to other forms. The law of conservation of energy (which says
that energy can change form but is never lost) ties together such topics as food calories, batteries, heat, light, and watch springs. Understanding this
law makes it easier to learn about the various forms energy takes and how they relate to one another. Apparently unrelated topics are connected
through broadly applicable physical laws, permitting an understanding beyond just the memorization of lists of facts.
The unifying aspect of physical laws and the basic simplicity of nature form the underlying themes of this text. In learning to apply these laws, you will,
of course, study the most important topics in physics. More importantly, you will gain analytical abilities that will enable you to apply these laws far
beyond the scope of what can be included in a single book. These analytical skills will help you to excel academically, and they will also help you to
think critically in any professional career you choose to pursue. This module discusses the realm of physics (to define what physics is), some
applications of physics (to illustrate its relevance to other disciplines), and more precisely what constitutes a physical law (to illuminate the importance
of experimentation to theory).
Science and the Realm of Physics
Science consists of the theories and laws that are the general truths of nature as well as the body of knowledge they encompass. Scientists are
continually trying to expand this body of knowledge and to perfect the expression of the laws that describe it.Physicsis concerned with describing
the interactions of energy, matter, space, and time, and it is especially interested in what fundamental mechanisms underlie every phenomenon. The
concern for describing the basic phenomena in nature essentially defines therealm of physics.
Physics aims to describe the function of everything around us, from the movement of tiny charged particles to the motion of people, cars, and
spaceships. In fact, almost everything around you can be described quite accurately by the laws of physics. Consider a smart phone (Figure 1.3).
Physics describes how electricity interacts with the various circuits inside the device. This knowledge helps engineers select the appropriate materials
and circuit layout when building the smart phone. Next, consider a GPS system. Physics describes the relationship between the speed of an object,
the distance over which it travels, and the time it takes to travel that distance. When you use a GPS device in a vehicle, it utilizes these physics
equations to determine the travel time from one location to another.
12 CHAPTER 1 | INTRODUCTION: THE NATURE OF SCIENCE AND PHYSICS
This content is available for free at http://cnx.org/content/col11406/1.7
Figure 1.3The Apple “iPhone” is a common smart phone with a GPS function. Physics describes the way that electricity flows through the circuits of this device. Engineers
use their knowledge of physics to construct an iPhone with features that consumers will enjoy. One specific feature of an iPhone is the GPS function. GPS uses physics
equations to determine the driving time between two locations on a map. (credit: @gletham GIS, Social, Mobile Tech Images)
Applications of Physics
You need not be a scientist to use physics. On the contrary, knowledge of physics is useful in everyday situations as well as in nonscientific
professions. It can help you understand how microwave ovens work, why metals should not be put into them, and why they might affect pacemakers.
(SeeFigure 1.4andFigure 1.5.) Physics allows you to understand the hazards of radiation and rationally evaluate these hazards more easily.
Physics also explains the reason why a black car radiator helps remove heat in a car engine, and it explains why a white roof helps keep the inside of
a house cool. Similarly, the operation of a car’s ignition system as well as the transmission of electrical signals through our body’s nervous system are
much easier to understand when you think about them in terms of basic physics.
Physics is the foundation of many important disciplines and contributes directly to others. Chemistry, for example—since it deals with the interactions
of atoms and molecules—is rooted in atomic and molecular physics. Most branches of engineering are applied physics. In architecture, physics is at
the heart of structural stability, and is involved in the acoustics, heating, lighting, and cooling of buildings. Parts of geology rely heavily on physics,
such as radioactive dating of rocks, earthquake analysis, and heat transfer in the Earth. Some disciplines, such as biophysics and geophysics, are
hybrids of physics and other disciplines.
Physics has many applications in the biological sciences. On the microscopic level, it helps describe the properties of cell walls and cell membranes
(Figure 1.6andFigure 1.7). On the macroscopic level, it can explain the heat, work, and power associated with the human body. Physics is involved
in medical diagnostics, such as x-rays, magnetic resonance imaging (MRI), and ultrasonic blood flow measurements. Medical therapy sometimes
directly involves physics; for example, cancer radiotherapy uses ionizing radiation. Physics can also explain sensory phenomena, such as how
musical instruments make sound, how the eye detects color, and how lasers can transmit information.
It is not necessary to formally study all applications of physics. What is most useful is knowledge of the basic laws of physics and a skill in the
analytical methods for applying them. The study of physics also can improve your problem-solving skills. Furthermore, physics has retained the most
basic aspects of science, so it is used by all of the sciences, and the study of physics makes other sciences easier to understand.
Figure 1.4The laws of physics help us understand how common appliances work. For example, the laws of physics can help explain how microwave ovens heat up food, and
they also help us understand why it is dangerous to place metal objects in a microwave oven. (credit: MoneyBlogNewz)
CHAPTER 1 | INTRODUCTION: THE NATURE OF SCIENCE AND PHYSICS S 13
C# Word - Split Word Document in C#.NET
C# DLLs: Split Word File. Add references: RasterEdge.Imaging.Basic.dll. using RasterEdge.XDoc.Word; Split Word file into two files in C#. split pdf by bookmark; break password on pdf
Figure 1.5These two applications of physics have more in common than meets the eye. Microwave ovens use electromagnetic waves to heat food. Magnetic resonance
imaging (MRI) also uses electromagnetic waves to yield an image of the brain, from which the exact location of tumors can be determined. (credit: Rashmi Chawla, Daniel
Smith, and Paul E. Marik)
Figure 1.6Physics, chemistry, and biology help describe the properties of cell walls in plant cells, such as the onion cells seen here. (credit: Umberto Salvagnin)
Figure 1.7An artist’s rendition of the the structure of a cell membrane. Membranes form the boundaries of animal cells and are complex in structure and function. Many of the
most fundamental properties of life, such as the firing of nerve cells, are related to membranes. The disciplines of biology, chemistry, and physics all help us understand the
membranes of animal cells. (credit: Mariana Ruiz)
Models, Theories, and Laws; The Role of Experimentation
The laws of nature are concise descriptions of the universe around us; they are human statements of the underlying laws or rules that all natural
processes follow. Such laws are intrinsic to the universe; humans did not create them and so cannot change them. We can only discover and
understand them. Their discovery is a very human endeavor, with all the elements of mystery, imagination, struggle, triumph, and disappointment
inherent in any creative effort. (SeeFigure 1.8andFigure 1.9.) The cornerstone of discovering natural laws is observation; science must describe
the universe as it is, not as we may imagine it to be.
14 CHAPTER 1 | INTRODUCTION: THE NATURE OF SCIENCE AND PHYSICS
This content is available for free at http://cnx.org/content/col11406/1.7
Figure 1.8Isaac Newton(1642–1727) was very reluctant to publish his revolutionary work and had to be convinced to do so. In his later years, he stepped down from his
academic post and became exchequer of the Royal Mint. He took this post seriously, inventing reeding (or creating ridges) on the edge of coins to prevent unscrupulous
people from trimming the silver off of them before using them as currency. (credit: Arthur Shuster and Arthur E. Shipley:Britain’s Heritage of Science. London, 1917.)
Figure 1.9Marie Curie(1867–1934) sacrificed monetary assets to help finance her early research and damaged her physical well-being with radiation exposure. She is the
only person to win Nobel prizes in both physics and chemistry. One of her daughters also won a Nobel Prize. (credit: Wikimedia Commons)
We all are curious to some extent. We look around, make generalizations, and try to understand what we see—for example, we look up and wonder
whether one type of cloud signals an oncoming storm. As we become serious about exploring nature, we become more organized and formal in
collecting and analyzing data. We attempt greater precision, perform controlled experiments (if we can), and write down ideas about how the data
may be organized and unified. We then formulate models, theories, and laws based on the data we have collected and analyzed to generalize and
communicate the results of these experiments.
Amodelis a representation of something that is often too difficult (or impossible) to display directly. While a model is justified with experimental proof,
it is only accurate under limited situations. An example is the planetary model of the atom in which electrons are pictured as orbiting the nucleus,
analogous to the way planets orbit the Sun. (SeeFigure 1.10.) We cannot observe electron orbits directly, but the mental image helps explain the
observations we can make, such as the emission of light from hot gases (atomic spectra). Physicists use models for a variety of purposes. For
example, models can help physicists analyze a scenario and perform a calculation, or they can be used to represent a situation in the form of a
computer simulation. Atheoryis an explanation for patterns in nature that is supported by scientific evidence and verified multiple times by various
groups of researchers. Some theories include models to help visualize phenomena, whereas others do not. Newton’s theory of gravity, for example,
does not require a model or mental image, because we can observe the objects directly with our own senses. The kinetic theory of gases, on the
other hand, is a model in which a gas is viewed as being composed of atoms and molecules. Atoms and molecules are too small to be observed
directly with our senses—thus, we picture them mentally to understand what our instruments tell us about the behavior of gases.
Alawuses concise language to describe a generalized pattern in nature that is supported by scientific evidence and repeated experiments. Often, a
law can be expressed in the form of a single mathematical equation. Laws and theories are similar in that they are both scientific statements that
result from a tested hypothesis and are supported by scientific evidence. However, the designationlawis reserved for a concise and very general
statement that describes phenomena in nature, such as the law that energy is conserved during any process, or Newton’s second law of motion,
which relates force, mass, and acceleration by the simple equation
. A theory, in contrast, is a less concise statement of observed
phenomena. For example, the Theory of Evolution and the Theory of Relativity cannot be expressed concisely enough to be considered a law. The
biggest difference between a law and a theory is that a theory is much more complex and dynamic. A law describes a single action, whereas a theory
explains an entire group of related phenomena. And, whereas a law is a postulate that forms the foundation of the scientific method, a theory is the
end result of that process.
Less broadly applicable statements are usually called principles (such as Pascal’s principle, which is applicable only in fluids), but the distinction
between laws and principles often is not carefully made.
CHAPTER 1 | INTRODUCTION: THE NATURE OF SCIENCE AND PHYSICS S 15
Figure 1.10What is a model? This planetary model of the atom shows electrons orbiting the nucleus. It is a drawing that we use to form a mental image of the atom that we
cannot see directly with our eyes because it is too small.
Models, Theories, and Laws
Models, theories, and laws are used to help scientists analyze the data they have already collected. However, often after a model, theory, or law
has been developed, it points scientists toward new discoveries they would not otherwise have made.
The models, theories, and laws we devise sometimesimply the existence of objects or phenomena as yet unobserved.These predictions are
remarkable triumphs and tributes to the power of science. It is the underlying order in the universe that enables scientists to make such spectacular
predictions. However, ifexperimentdoes not verify our predictions, then the theory or law is wrong, no matter how elegant or convenient it is. Laws
can never be known with absolute certainty because it is impossible to perform every imaginable experiment in order to confirm a law in every
possible scenario. Physicists operate under the assumption that all scientific laws and theories are valid until a counterexample is observed. If a
good-quality, verifiable experiment contradicts a well-established law, then the law must be modified or overthrown completely.
The study of science in general and physics in particular is an adventure much like the exploration of uncharted ocean. Discoveries are made;
models, theories, and laws are formulated; and the beauty of the physical universe is made more sublime for the insights gained.
The Scientific Method
As scientists inquire and gather information about the world, they follow a process called thescientific method. This process typically begins
with an observation and question that the scientist will research. Next, the scientist typically performs some research about the topic and then
devises a hypothesis. Then, the scientist will test the hypothesis by performing an experiment. Finally, the scientist analyzes the results of the
experiment and draws a conclusion. Note that the scientific method can be applied to many situations that are not limited to science, and this
method can be modified to suit the situation.
Consider an example. Let us say that you try to turn on your car, but it will not start. You undoubtedly wonder: Why will the car not start? You can
follow a scientific method to answer this question. First off, you may perform some research to determine a variety of reasons why the car will not
start. Next, you will state a hypothesis. For example, you may believe that the car is not starting because it has no engine oil. To test this, you
open the hood of the car and examine the oil level. You observe that the oil is at an acceptable level, and you thus conclude that the oil level is
not contributing to your car issue. To troubleshoot the issue further, you may devise a new hypothesis to test and then repeat the process again.
The Evolution of Natural Philosophy into Modern Physics
Physics was not always a separate and distinct discipline. It remains connected to other sciences to this day. The wordphysicscomes from Greek,
meaning nature. The study of nature came to be called “natural philosophy.” From ancient times through the Renaissance, natural philosophy
encompassed many fields, including astronomy, biology, chemistry, physics, mathematics, and medicine. Over the last few centuries, the growth of
knowledge has resulted in ever-increasing specialization and branching of natural philosophy into separate fields, with physics retaining the most
basic facets. (SeeFigure 1.11,Figure 1.12, andFigure 1.13.) Physics as it developed from the Renaissance to the end of the 19th century is called
classical physics. It was transformed into modern physics by revolutionary discoveries made starting at the beginning of the 20th century.
Figure 1.11Over the centuries, natural philosophy has evolved into more specialized disciplines, as illustrated by the contributions of some of the greatest minds in history.
The Greek philosopherAristotle(384–322 B.C.) wrote on a broad range of topics including physics, animals, the soul, politics, and poetry. (credit: Jastrow (2006)/Ludovisi
16 CHAPTER 1 | INTRODUCTION: THE NATURE OF SCIENCE AND PHYSICS
This content is available for free at http://cnx.org/content/col11406/1.7
Figure 1.12Galileo Galilei(1564–1642) laid the foundation of modern experimentation and made contributions in mathematics, physics, and astronomy. (credit: Domenico
Figure 1.13Niels Bohr(1885–1962) made fundamental contributions to the development of quantum mechanics, one part of modern physics. (credit: United States Library of
Congress Prints and Photographs Division)
Classical physics is not an exact description of the universe, but it is an excellent approximation under the following conditions: Matter must be
moving at speeds less than about 1% of the speed of light, the objects dealt with must be large enough to be seen with a microscope, and only weak
gravitational fields, such as the field generated by the Earth, can be involved. Because humans live under such circumstances, classical physics
seems intuitively reasonable, while many aspects of modern physics seem bizarre. This is why models are so useful in modern physics—they let us
conceptualize phenomena we do not ordinarily experience. We can relate to models in human terms and visualize what happens when objects move
at high speeds or imagine what objects too small to observe with our senses might be like. For example, we can understand an atom’s properties
because we can picture it in our minds, although we have never seen an atom with our eyes. New tools, of course, allow us to better picture
phenomena we cannot see. In fact, new instrumentation has allowed us in recent years to actually “picture” the atom.
Limits on the Laws of Classical Physics
For the laws of classical physics to apply, the following criteria must be met: Matter must be moving at speeds less than about 1% of the speed
of light, the objects dealt with must be large enough to be seen with a microscope, and only weak gravitational fields (such as the field generated
by the Earth) can be involved.
Figure 1.14Using a scanning tunneling microscope (STM), scientists can see the individual atoms that compose this sheet of gold. (credit: Erwinrossen)
Some of the most spectacular advances in science have been made in modern physics. Many of the laws of classical physics have been modified or
rejected, and revolutionary changes in technology, society, and our view of the universe have resulted. Like science fiction, modern physics is filled
with fascinating objects beyond our normal experiences, but it has the advantage over science fiction of being very real. Why, then, is the majority of
this text devoted to topics of classical physics? There are two main reasons: Classical physics gives an extremely accurate description of the
universe under a wide range of everyday circumstances, and knowledge of classical physics is necessary to understand modern physics.
CHAPTER 1 | INTRODUCTION: THE NATURE OF SCIENCE AND PHYSICS S 17
Modern physicsitself consists of the two revolutionary theories, relativity and quantum mechanics. These theories deal with the very fast and the
very small, respectively.Relativitymust be used whenever an object is traveling at greater than about 1% of the speed of light or experiences a
strong gravitational field such as that near the Sun.Quantum mechanicsmust be used for objects smaller than can be seen with a microscope. The
combination of these two theories isrelativistic quantum mechanics,and it describes the behavior of small objects traveling at high speeds or
experiencing a strong gravitational field. Relativistic quantum mechanics is the best universally applicable theory we have. Because of its
mathematical complexity, it is used only when necessary, and the other theories are used whenever they will produce sufficiently accurate results. We
will find, however, that we can do a great deal of modern physics with the algebra and trigonometry used in this text.
Check Your Understanding
A friend tells you he has learned about a new law of nature. What can you know about the information even before your friend describes the law?
How would the information be different if your friend told you he had learned about a scientific theory rather than a law?
Without knowing the details of the law, you can still infer that the information your friend has learned conforms to the requirements of all laws of
nature: it will be a concise description of the universe around us; a statement of the underlying rules that all natural processes follow. If the
information had been a theory, you would be able to infer that the information will be a large-scale, broadly applicable generalization.
PhET Explorations: Equation Grapher
Learn about graphing polynomials. The shape of the curve changes as the constants are adjusted. View the curves for the individual terms (e.g.
) to see how they add to generate the polynomial curve.
Figure 1.15Equation Grapher (http://cnx.org/content/m42092/1.4/equation-grapher_en.jar)
1.2Physical Quantities and Units
Figure 1.16The distance from Earth to the Moon may seem immense, but it is just a tiny fraction of the distances from Earth to other celestial bodies. (credit: NASA)
The range of objects and phenomena studied in physics is immense. From the incredibly short lifetime of a nucleus to the age of the Earth, from the
tiny sizes of sub-nuclear particles to the vast distance to the edges of the known universe, from the force exerted by a jumping flea to the force
between Earth and the Sun, there are enough factors of 10 to challenge the imagination of even the most experienced scientist. Giving numerical
values for physical quantities and equations for physical principles allows us to understand nature much more deeply than does qualitative
description alone. To comprehend these vast ranges, we must also have accepted units in which to express them. And we shall find that (even in the
potentially mundane discussion of meters, kilograms, and seconds) a profound simplicity of nature appears—all physical quantities can be expressed
as combinations of only four fundamental physical quantities: length, mass, time, and electric current.
We define aphysical quantityeither byspecifying how it is measuredor bystating how it is calculatedfrom other measurements. For example, we
define distance and time by specifying methods for measuring them, whereas we defineaverage speedby stating that it is calculated as distance
traveled divided by time of travel.
Measurements of physical quantities are expressed in terms ofunits, which are standardized values. For example, the length of a race, which is a
physical quantity, can be expressed in units of meters (for sprinters) or kilometers (for distance runners). Without standardized units, it would be
extremely difficult for scientists to express and compare measured values in a meaningful way. (SeeFigure 1.17.)
18 CHAPTER 1 | INTRODUCTION: THE NATURE OF SCIENCE AND PHYSICS
This content is available for free at http://cnx.org/content/col11406/1.7
Documents you may be interested
Documents you may be interested