As we look around us we see a world full of "things": machines, devices, tools; things that we have designed, built, and used; things made of wood, metals, ceramics, and plastics. We know from experience that some things are better than others; they last longer, cost less, are quieter, look better, or are easier to use.

Ideally, however, every such item has been designed according to some set of "functional requirements" as perceived by the designers-that is, it has been designed so as to answer the question,?"Exactly what function should it perform?" In the world of engineering, the major function frequently is to support some type of?loading due to weight, inertia, pressure etc. From the beams in our homes to the wings of an airplane, there must be an appropriate melding of materials, dimensions, and fastenings to produce structures that will perform their functions reliably for a reasonable cost over a reasonable lifetime.

In practice, engineering mechanics methods are used in two quite?different ways:

1. The development of any new device requires an interactive, iterative consideration of form, size, materials, loads, durability, safety, and cost.

2. When a device fails (unexpectedly) it is often necessary to carry out a study to pinpoint the cause of failure and to identify potential corrective measures. Our best designs often evolve through a successive elimination of weak points.

To many engineers, both of the above processes can prove to be absolutely fascinating and enjoyable, not to mention ( at times) lucrative.

In any " real"?problem there is never sufficient good, useful?information; we seldom know the actual loads and operating conditions with any precision, and the analyses are seldom exact. While our mathematics may be precise, the overall analysis is generally only approximate, and different skilled people can obtain different solutions. In the study of engineering mechanics most of the problems will be sufficiently " idealized" to permit unique solutions, but it should be clear that the

"real world" is far less idealized, and that?you usually will have to perform some idealization in order to obtain a solution.

The technical areas we will consider are frequently called?"statics" and "strength of materials," "statics" referring to the study?of forces acting on stationary devices, and "strength of materials" referring to the effects of those forces on the structure ( deformations, load limits, etc. ).

While a great many devices are not, in fact, static, the methods developed here are perfectly applicable to dynamic situations if the extra loadings?associated with the dynamics are taken into account.?Whenever the dynamic forces are small relative to the static loadings, the system is usually considered to be static.

In engineering mechanics, we will begin to appreciate the various types of approximations that are inherent in any real problem:

Primarily, we will be discussing things which are in?"equilibrium," i.e., not accelerating. However, if we look closely enough, everything is accelerating.

We will consider many structural members to be "weightless"-but they never are.

We will deal with forces that act at a "point"-?but all forces act over an area.

We will consider some parts to be "rigid" - but all bodies will deform under load.

We will make many assumptions that clearly are false. But these assumptions should always render the problem easier, more tractable.?You will discover that the goal is to make as many simplifying assumptions as possible without seriously degrading the result.

?Generally there is no clear method to determine how completely, or how precisely, to treat a problem. If our analysis is too simple, we may not get a pertinent answer; if our analysis is too detailed, we may not be able to obtain any answer. It is usually preferable to start with a relatively simple analysis and then add more detail as required to obtain a practical solution.

During the past two decades, there has been a tremendous growth in the availability of computerized methods for solving problems that previously were beyond solution because the time required to solve them would have been prohibitive. At the same time the cost of computers has decreased by orders of magnitude. The computer programs not only remove the drudgery of computation, they allow fairly complicated problems to be solved with ease. Students gain a greater understanding of the subject by simply changing input values and seeing what happens.