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chapter_1 - Thousands of years ago people in southern...

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1 1 CHAPTER Introduction O U T L I N E 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 Significant Figures 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 Stone/Getty Images 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 defined. For example, if our fundamental unit of length is defined 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 defined 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.
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2 Chapter 1 Introduction Length In 1799, the legal standard of length in France became the meter, defined as one ten- millionth of the distance from the equator to the North Pole. Until 1960, the official length of the meter was the distance between two lines on a specific bar of platinum- iridium alloy stored under controlled conditions. This standard was abandoned for several reasons, the principal one being that measurements of the separation be- tween the lines are not precise enough. In 1960, the meter was defined as 1 650
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