1
1
CHAPTER
Introduction
OUTLINE
1.1
Standards of Length,
Mass, and Time
1.2
The Building Blocks
of Matter
1.3
Dimensional Analysis
1.4
Uncertainty in
Measurement and
SigniFcant ±igures
1.5
Conversion of Units
1.6
Estimates and
Order-of-Magnitude
Calculations
1.7
Coordinate Systems
1.8
Trigonometry
1.9
Problem-Solving Strategy
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The goal of physics is to provide an understanding of the physical world by developing theo-
ries based on experiments. A physical theory is essentially a guess, usually expressed mathe-
matically, about how a given physical system works. The theory makes certain predictions
about the physical system which can then be checked by observations and experiments. If the
predictions turn out to correspond closely to what is actually observed, then the theory
stands, although it remains provisional. No theory to date has given a complete description of
all physical phenomena, even within a given subdiscipline of physics. Every theory is a work in
progress.
The basic laws of physics involve such physical quantities as force, velocity, volume, and
acceleration, all of which can be described in terms of more fundamental quantities. In me-
chanics, the three most fundamental quantities are
length
(L),
mass
(M), and
time
(T); all
other physical quantities can be constructed from these three.
1.1
STANDARDS OF LENGTH, MASS, AND TIME
To communicate the result of a measurement of a certain physical quantity, a
unit
for the quantity must be deFned. ±or example, if our fundamental unit of length is
deFned to be 1.0 meter, and someone familiar with our system of measurement re-
ports that a wall is 2.0 meters high, we know that the height of the wall is twice the
fundamental unit of length. Likewise, if our fundamental unit of mass is deFned as
1.0 kilogram, and we are told that a person has a mass of 75 kilograms, then that
person has a mass 75 times as great as the fundamental unit of mass.
In 1960, an international committee agreed on a standard system of units for
the fundamental quantities of science, called
SI
(Système International). Its units
of length, mass, and time are the meter, kilogram, and second, respectively.
Thousands of years ago, people in
southern England built Stonehenge,
which was used as a calendar. The
position of the sun and stars relative
to the stones determined seasons for
planting or harvesting.
Throughout
the text, the PhysicsNow icon indi-
cates an opportunity for you to test
yourself on key concepts and to
explore animations and interactions
on the PhysicsNow website at
www.cp7e.com.