# Engineering Mechanics: Dynamics

## Introduction/Purpose

The first edition of this text was published in 1993 by John Wiley & Sons, Inc. The second edition was published in 1996. Our purpose in writing this Dynamics book, together with the companion Statics book, was to present a fresh look at the subject and to provide a more logical order of presentation of the subject material. We believe that our order of presentation will give students a greater understanding of the material and will better prepare students for future courses and later professional life.

## Organization

This volume on Dynamics breaks away from the traditional organization of first covering all aspects of particle dynamics and then covering all aspects of rigid-body dynamics. The description of particle kinematics (Chapter 13) is followed immediately by a description of rigid-body kinematics (Chapter 14). For a course covering both particle and rigid-body kinematics, we believe that it is more logical and efficient to cover all kinematics at one time and in one place.

Similarly, the use of the Force-Mass-Acceleration (Newton's Second Law) method to solve particle kinetics problems (Chapter 15) is followed immediately by the use of the Force-Mass-Acceleration method to solve rigid-body kinetics problems (Chapter 16). These four chapters form a complete, albeit brief, introduction to the dynamics of particles and rigid bodies.

The following four chapters present two alternative methods of solving certain types of problems. First, the work-energy method is used to solve particle kinetics problems (Chapter 17) and rigid-body kinetics problems (Chapter 18). Next, the impulse-momentum method is used to solve particle kinetics problems (Chapter 19) and rigid-body kinetics problems (Chapter 20).

The final chapter (Chapter 21) presents an introduction to mechanical vibrations. In this chapter, the principles of kinetics are used to develop the differential equations of motion in problems that involve vibratory or oscillatory motion. These equations are then solved using principles of differential equations. This chapter is included for those instructors who feel that no introductory course is complete without at least an introduction to vibrations.

An additional benefit of this organization of topics is that the more challenging topics are spread more uniformly over the quarter or semester. In each of the major sections of the book, the progression of material is from the slightly familiar (from a previous physics course) topics of particle mechanics to the unfamiliar concepts of two-dimensional rigid-body mechanics to the more complex concepts of three-dimensional rigid-body motion.

## Engineering Emphasis

Throughout this book, strong emphasis has been placed on the engineering significance of the subject area in addition to the mathematical methods of analysis. Many illustrative example problems have been integrated into the main body of the text at points where the presentation of a method can be best reinforced by the immediate illustration of the method. Students are usually more enthusiastic about a subject if they can see and appreciate its value as they proceed into the subject.

We believe that students can progress in a mechanics course only by understanding the physical and mathematical principles jointly, not by mere memorization of formulas and substitution of data to obtain answers to simple problems. Furthermore, we think that it is better to teach a few fundamental principles for solving problems than to teach a large number of special cases and trick procedures. Therefore, the text aims to develop in the student the ability to analyze a given problem in a simple and logical manner and to apply a few fundamental, well-understood principles to its solution.

A conscientious effort has been made to present the material in a simple and direct manner, with the student's point of view constantly in mind. Clarity is never sacrificed for the sake of mathematical elegance. Calculus and vector algebra are used wherever it provides an efficient solution to a problem. However, if formal vector algebra offers no advantage, then a scalar or geometric-vector approach is used instead. Likewise, students are encouraged to develop the ability to select the mathematical tools most appropriate for the particular problem they are attempting to solve.

## Sample Syllabi

Because we have been asked, we make available the following abbreviated syllabi for courses using our Statics and Dynamics texts. The following pointers are to 30-hour (3 quarter credit or 2 semester credit), 40-hour (4 quarter credit), 45-hour (3 semester credit), 50-hour (5 quarter credit), and 60-hour (6 quarter credit or 4 semester credit) variants of the Dynamics syllabus as well as a 75-hour (5 semester credit) variant of a combined Statics/Dynamics syllabus.

These syllabi are purposely vague and obviously are only a few of the many variations possible. More detailed syllabi will depend on whether the courses are intended primarily for civil engineering students or for mechanical engineering students; on whether the courses are primarily taken by freshman students or sophomore students; on whether the students will be taking additional mechanics courses or not; etc.

However, we hope that these brief outlines will be useful to instructors as you make up your syllabi.

An abbreviated syllabus for a 3 quarter credit or a 2 semester credit Dynamics course.

An abbreviated syllabus for a 4 quarter credit Dynamics course.

An abbreviated syllabus for a 3 semester credit Dynamics course.

An abbreviated syllabus for a 5 quarter credit Dynamics course.

An abbreviated syllabus for a 6 quarter credit or a 4 semester credit Dynamics course.

An abbreviated syllabus for a 5 semester credit Combined Statics and Dynamics course.

Comments and suggestions should be sent to:
 sturges@iastate.edu Leroy D. Sturges 2019 Black Engineering Iowa State University Ames, Iowa 50011-2162 515-294-6242

©1998, Leroy D. Sturges (revised 3 August 1998)