The question: "Why do we believe in atoms and their properties?" provides the theme for this text suitable for the first semester of a two- or three-term introductory physics course or for a one-term course for non-scientists. The book thus covers much of 19th and 20th century physics, but it also connects these topics to classical physics. The treatment emphasizes quantitative reasoning and analysis: how are the ideas of physics inferred from the data, and how are the data acquired?

This novel text structures a one-semester course of introductory physics around the question: "Why do we believe in atoms and their properties?" After a brief review of the basic terminology of mechanics, the book begins by introducing the atoms of chemistry. It then turns to the physicists hard-sphere atoms: ideal gases, pressure, temperature, viscosity. The first hint of subatomic structure comes from the discovery of the electron, and the discussion thus turns to electricity, magnetism, light, and x- rays. This leads in turn to waves and relativity, and the book concludes with modern insights into the atom: photons radioactivity, the particle/wave duality, quantum mechanics, the Bohr model, and closes the circle back to the chemists atom with Moseleys law and the periodic table. A large number of problems, some of them based on computer spreadsheets, as well as laboratory exercises serve to clarify students' understanding.

1 What's Going On Here?.- 2 Some Physics You Need to Know.- 3 The Chemist's Atoms.- 4 Gas Laws.- 5 Hard-Sphere Atoms.- 6 Electric Forces and Fields.- 7 Magnetic Field and Magnetic Force.- 8 Electrical Atoms and the Electron.- 9 Waves and Light.- 10 Time and Length at High Speeds.- 11 Energy and Momentum at High Speeds.- 12 The Granularity of Light.- 13 X-Rays.- 14 Particles as Waves.- 15 The Heisenberg Uncertainty Principle.- 16 Radioactivity and the Atomic Nucleus.- 17 Spectra and the Bohr Atom.- 18 Epilogue.- A Useful Information.- A.1 SI Prefixes.- A.2 Basic Physical Constants.- A.3 Constants That You Must Know.- A.4 Some Units and Their Abbreviations.- A.5 Atomic Masses.- A.6 Masses of Nuclides.- A.7 Miscellaneous.