The world of mechanics


The concept embodied within the word “design” is more properly termed synthesis, the method of contriving a scheme or a way of accomplishing a given purpose.

Design is that the process of prescribing the sizes, shapes, material compositions, and arrangements of parts so the resulting machine will perform the prescribed task.

Although there are many phases within the design process which will be approached during a well-ordered, scientific manner, the general process is by its very nature the maximum amount an art as a science.

It entails imagination, intuition, creativity, judgment, and knowledge.

The role of science within the design process is just to supply tools to be employed by designers as they practice their art.

In the process of evaluating the assorted interacting alternatives, designers find a necessity for an oversized collection of mathematical and scientific tools.

Thus, the tools are of tremendous help when making a decision among alternatives.

However, scientific tools cannot make decisions for designers; designers have every right to exert their imagination and inventive abilities, even to the extent of overruling the mathematical recommendations. Probably the most important collection of scientific methods at the designer’s disposal falls into the category called analysis.

These are techniques that allow the designer to critically examine an already existing, or proposed, design to guage its suitability for the task.

Thus, analysis in itself isn’t an original science but one amongst evaluation and rating things already conceived. we should always bear in mind that, although most of our effort could also be spent on analysis, the important goal is synthesis: the look of a machine or system.

Analysis is just a tool; however, it’s an important tool and can inevitably be used united step within the design process.


Statics deals with the analysis of stationary systems—that is, those within which time isn’t a factor—and dynamics deals with systems that change with time.

The investigation of the motion of a rigid body is also conveniently separated into two parts, the one, geometrical, and also the other mechanical. within the first part, the transference of the body from a given position to the other position must be investigated without relevancy the causes of the motion, and must be represented by analytical formulae, which is able to define the position of every point of the body. This investigation will therefore be referable solely to geometry, or rather to stereotomy [the art of stonecutting, now cited as descriptive geometry].

It is clear that by the separation of this a part of the question from the opposite, which belongs properly to Mechanics, the determination of the motion from dynamical principles are made much easier than if the 2 parts were undertaken conjointly.

These two aspects of dynamics were later recognized because the distinct sciences of kinematics were a term coined by Ampère∗ and derived from the Greek word kinema, meaning motion) and kinetics and handle motion and also the forces producing the motion, respectively.

The initial problem within the design of a system, therefore, is knowing the kinematics. Kinematics is that the study of motion, quite except the forces that produce the motion.

In particular, kinematics is that the study of position, displacement, rotation, speed, velocity, acceleration, and jerk. The study, say, of planetary or rotation is additionally a controversy in kinematics, but during this book, we shall concentrate our attention on kinematic problems that arise within the design and operation of mechanical systems.

Thus, the kinematics of machines and mechanisms is that the focus of the following several chapters of this book. additionally, statics and kinetics are vital parts of an entire design analysis, and that they also are covered in later chapters.

It should be carefully noted within the previous quotation that Euler based his separation of dynamics into kinematics and kinetics on the belief that they cater to rigid bodies.

It is this important assumption that permits the 2 to be treated separately.

For flexible bodies, the shapes of the bodies themselves, and so their motions, depend upon the forces exerted on them.

In this situation, the study of force and motion must occur simultaneously, thus significantly increasing the complexity of the analysis.

Fortunately, although all real machine parts are flexible to a point, machines are usually designed from relatively rigid materials, keeping part deflections to a minimum.

Therefore, it’s common practice to assume that deflections are negligible and parts are rigid while analyzing a machine’s kinematic performance then, during dynamic analysis when loads are sought, to style the parts in order that the idea is justified.

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