Fisica

P U Z Z L E R
For thousands of years the spinning Earth provided a natural standard for our measurements of time. However, since 1972 we have added more than 20 “leap seconds” to our clocks to keep them synchronized to the Earth. Why are such adjustments needed? What does it take to be a good standard? (Don Mason/The
Stock Market and NASA)

c h a p t e r

Physics and Measurement

Chapter Outline
1.1 Standards of Length, Mass, and
Time

1.5 Conversion of Units 1.6 Estimates and Order-of-Magnitude
Calculations

1.2 The Building Blocks of Matter 1.3 Density 1.4 Dimensional Analysis

1.7 Significant Figures

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ike all other sciences, physics is based on experimental observations and quantitative measurements. The main objective of physics is to find the limited number of fundamental laws that govern natural phenomena and to use them to develop theories that can predict the results of future experiments. The fundamental laws used in developing theories are expressed in the language of mathematics, the tool that provides a bridge between theory and experiment. When a discrepancy between theory and experiment arises, new theories must be formulated to remove the discrepancy. Many times a theory is satisfactory only under limited conditions; a more general theory might be satisfactory without such limitations. For example, the laws of motion discovered by Isaac Newton (1642 – 1727) in the 17th century accurately describe the motion of bodies at normal speeds but do not apply to objects moving at speeds comparable with the speed of light. In contrast, the special theory of relativity developed by Albert Einstein (1879 – 1955) in the early 1900s gives the same results as Newton’s laws at low speeds but also correctly describes motion at speeds approaching the speed of light. Hence, Einstein’s is a more general theory of motion. Classical physics, which means all of the physics developed before 1900, includes the theories, concepts, laws, and