A basic, non-mathematical textbook for non-science students in secondary school or college. The book is based on Robert Karplus' many years of research on how beginners think about physics. In the "modeling approach" students explore and test simple analog, working and mathematical models for physical phenomena. The models provide a clear, understandable transition to the key principles and theories of physics. The book begins with the basic concepts of relative motion, reference frames, interaction, systems, and a descriptive overview of energy transfer. Subsequent chapters develop the details of temperature and heat, thermal (internal) energy, forces and work, electrical energy and electrical circuits, velocity and acceleration, Newton's Laws, motion near the surface of the earth, periodic and circular motion, celestial mechanics and gravity, pressure and kinetic theory, light and sound, waves, and modern physics (Bohr model and the basics of quantum mechanics). The "Modeling Instruction" approach is used in secondary schools throughout the US (see modeling.asu.edu). This book is especially useful in conjunction with (or as preparation for) the study of chemistry.