The essential skills of modeling - abstraction, analysis, simulation, and vali-dation - are central in engineering, natural sciences, social sciences, medicine,and many other fields. Some students learn these skills implicitly, but in mostschools they are not taught explicitly, and students get little practice. That'sthe problem this book is meant to address.At Olin College, we use this book in a class called Modeling and Simulation,which all students take in their first semester. My colleagues, John Geddesand Mark Somerville, and I developed this class and taught it for the first timein 2009.It is based on our belief that modeling should be taught explicitly, early, andthroughout the curriculum. It is also based on our conviction that computationis an essential part of this process.If students are limited to the mathematical analysis they can do by hand, theyare restricted to a small number of simple physical systems, like a projectilemoving in a vacuum or a block on a frictionless plane.And they will only work with bad models; that is, models that are too simplefor their intended purpose. In nearly every mechanical system, air resistanceand friction are essential features; if we ignore them, our predictions will bewrong and our designs won't work.In most freshman physics classes, students don't make modeling decisions;sometimes they are not even aware of the decisions that have been made forthem. Our goal is to teach the entire modeling process and give students achance to practice it.