This book grew out of an ongoing effort to modernize Colgate University's three-term, introductory, calculus-Ievel physics course. The book is for the first term of this course and is intended to help first-year college students make a good transition from high-school physics to university physics. The book concentrates on the physics that explains why we believe in the existence of atoms and their properties. This story line, which motivates much of our professional research, has helped us limit the material presented to a more humane and more realistic amount than is presented in many beginning university physics courses. The theme of atoms also supports the presentation of more non-Newtonian topics and ideas than is customary in the first term of calculus-Ievel physics. We think it is important and desirable to introduce students sooner than usual to some of the major ideas that shape contemporary physicists' views of the nature and behavior of matter. On the verge of the twenty-first century such a goal seems particularly appropriate.